310T Truck and Coach Technician Exam — Questions and Answers

Question 1: A technician who holds the 310T certification and wants to advance into diagnostics and electronics should prioritize obtaining which type of additional training?

Advanced electrical/electronic systems and CAN bus diagnostics training (Correct answer)
Hydraulic brake bleeding procedures refresher
Tire retreading and recapping certification
Body and paint restoration courses

Correct answer: Advanced electrical/electronic systems and CAN bus diagnostics training

Modern trucks rely heavily on CAN bus networks and electronic control modules, so advanced diagnostics training prepares technicians for complex troubleshooting roles that command higher pay.

Question 2: When performing a diesel engine compression test, a reading of 380 psi on one cylinder versus 480 psi on all others indicates:

Incorrect test procedure
Faulty compression gauge
Worn or damaged rings or valves in that cylinder (Correct answer)
Normal variation within specification

Correct answer: Worn or damaged rings or valves in that cylinder

A cylinder reading more than 10% below the average indicates internal sealing problems such as worn rings, damaged valves, or a blown head gasket.

Question 3: When replacing a diesel fuel injector, why must the injector hold-down torque be tightened to specification?

To compress the fuel return fitting for a leak-free connection
To ensure the injector electrical connector seats properly
To align the injector spray pattern with the piston bowl
To prevent combustion gas blow-by past the injector seat and seal (Correct answer)

Correct answer: To prevent combustion gas blow-by past the injector seat and seal

Proper torque ensures the injector sealing washer or copper crush washer seats correctly, preventing high-pressure combustion gases from escaping past the injector.

Question 4: A heavy-duty truck experiences a vibration that increases with vehicle speed but is NOT affected by engine RPM. The MOST likely cause is:

Driveshaft imbalance or worn U-joints (Correct answer)
Faulty torque converter
Worn clutch disc
Worn engine mounts

Correct answer: Driveshaft imbalance or worn U-joints

A speed-related vibration independent of engine RPM points to the driveshaft or U-joints rather than engine components.

Question 5: Scrub radius is defined as the distance between:

The king pin and the wheel center at hub height
The center of the tire contact patch and the vehicle centerline
The point where the steering axis intersects the ground and the center of the tire contact patch (Correct answer)
The two front tire contact patches

Correct answer: The point where the steering axis intersects the ground and the center of the tire contact patch

Scrub radius (also called steering offset) is measured at ground level between the steering axis projection point and the tire center — it affects steering returnability and torque steer.

Question 6: A technician notices the air pressure in one air spring on a rear tag axle is significantly lower than the other side. What is the MOST likely result?

Increased caster on the tag axle
Higher than normal toe-out on turns
Uneven load distribution causing axle thrust angle change (Correct answer)
Reduced Ackermann effect

Correct answer: Uneven load distribution causing axle thrust angle change

Unequal air spring pressure causes one side of the axle to ride lower, shifting the axle and altering its thrust angle relative to the vehicle centerline.

Question 7: When performing a stall test on a torque converter, what does a stall speed BELOW the manufacturer's specification indicate?

Slipping clutch packs inside the transmission
A faulty torque converter stator one-way clutch
Excessive transmission fluid pressure
Low engine power or a seized stator (Correct answer)

Correct answer: Low engine power or a seized stator

A stall speed below spec indicates the engine cannot develop enough power, or the stator is seized and is not allowing proper fluid coupling multiplication.

Question 8: Which axle configuration uses a single drive axle with the differential placed ahead of the axle centerline to allow a lower floor height?

Portal axle
Banjo axle
Hypoid axle
Drop-center (lowered) axle with forward-mounted differential (Correct answer)

Correct answer: Drop-center (lowered) axle with forward-mounted differential

A forward-differential drop-center axle shifts the differential forward of the wheel centerline, lowering the driveshaft tunnel and floor.

Question 9: A coach's electric wheelchair lift fails to operate. The motor does not run and no fault codes are stored. What should the technician check FIRST?

Interlock switches (door open, vehicle parked, kneeling system engaged) (Correct answer)
Lift motor winding resistance
Lift ECU power supply
Main power relay coil resistance

Correct answer: Interlock switches (door open, vehicle parked, kneeling system engaged)

Wheelchair lift systems require multiple interlocks to be satisfied before operation; an unsatisfied interlock prevents operation without setting a fault code.

Question 10: What does it indicate when a brake chamber push rod stroke exceeds the maximum allowable limit?

The brakes are over-adjusted and applying too tightly
The brakes are under-adjusted or excessively worn, reducing braking effectiveness (Correct answer)
The push rod is too short and must be replaced
The brakes are correctly adjusted

Correct answer: The brakes are under-adjusted or excessively worn, reducing braking effectiveness

Excess push rod stroke means the brakes require more travel to apply, indicating under-adjustment or worn linings that must be corrected immediately.

Question 11: What is a common cause of brake chamber pushrod stroke being TOO SHORT (under-travel)?

Relay valve failure
Worn brake lining
Leaking diaphragm
Slack adjuster adjusted too tightly (over-adjusted) (Correct answer)

Correct answer: Slack adjuster adjusted too tightly (over-adjusted)

Over-adjustment of the slack adjuster brings the lining too close to the drum, shortening stroke but also risking brake drag and heat buildup.

Question 12: Which skill is assessed during the practical exam for certification?

Customer service communication skills
Driving proficiency
Vehicle cleaning and maintenance
Diagnosing and repairing mechanical issues (Correct answer)

Correct answer: Diagnosing and repairing mechanical issues

The practical exam for Truck and Coach Technician certification specifically assesses a candidate's hands-on ability to diagnose, troubleshoot, and effectively repair various mechanical and electrical issues in heavy vehicles. This ensures they can apply their theoretical knowledge to real-world scenarios safely and efficiently, demonstrating practical competence.

Question 13: A coach engine develops a 'fuel knock' that is distinct from normal diesel combustion knock. What condition causes fuel knock?

Injector dribble depositing raw fuel that ignites late
High cetane fuel burning too slowly
Over-advanced injection timing causing rapid pressure rise (Correct answer)
Low engine oil pressure reducing injector lubrication

Correct answer: Over-advanced injection timing causing rapid pressure rise

Over-advanced injection timing causes fuel to ignite too early, creating an abnormally rapid pressure rise rate that produces a characteristic sharp knock.

Question 14: An articulated motor coach uses a hydraulic variable-ratio rack-and-pinion steering system. The driver reports that steering effort is normal at low speeds but becomes excessively heavy only during high-speed lane changes. A pressure test shows pump output is within specification at idle and at governed RPM. What is the MOST likely cause?

A sticking spool valve in the steering gear that fails to meter flow under rapid input rates (Correct answer)
A faulty vehicle speed sensor signal causing the variable-ratio controller to command maximum assist reduction at all speeds
Worn rack bushings causing the rack to bind under high lateral load conditions
A partially restricted power steering cooler reducing flow only under high-demand events

Correct answer: A sticking spool valve in the steering gear that fails to meter flow under rapid input rates

In a hydraulic variable-ratio system, heavy steering specifically during rapid inputs (lane changes) but not during slow maneuvers points to a spool valve response problem. The spool valve meters assist pressure proportionally to steering rate and load; if it sticks or has excessive friction, it cannot respond quickly enough to sudden high-demand inputs, starving assist during the critical moment. A cooler restriction affects sustained flow, not transient response. Rack bushing wear causes mechanical looseness, not heaviness. A faulty speed sensor would cause incorrect assist at all speeds, not only during high-rate inputs.

Question 15: When performing a PM inspection on a diesel engine, the technician finds the crankcase ventilation tube heavily coated with thick black sludge. What is the MOST likely cause?

Engine oil overdue for change or severe ring blow-by (Correct answer)
Incorrect viscosity oil used at the last service
Coolant leaking into the crankcase
Normal blow-by accumulation requiring only cleaning

Correct answer: Engine oil overdue for change or severe ring blow-by

Heavy sludge in the crankcase ventilation system indicates either severely degraded oil or excessive combustion blow-by past worn piston rings.

Question 16: During a 'dry park check,' an assistant rocks the steering wheel back and forth while the truck's full weight is on the ground. The technician observes vertical (up-and-down) movement in the drag link where it connects to the steering arm. This observation indicates:

A worn pitman arm
Normal component movement
A worn drag link socket (Correct answer)
Loose steering gear mounting bolts

Correct answer: A worn drag link socket

A dry park check is designed to identify looseness in steering components under normal load. Rotational or horizontal movement in the drag link is normal, but any vertical play within the ball-and-socket joint indicates excessive wear. The component with vertical play must be replaced.

Question 17: When checking the fifth wheel on a semi-truck during a PM inspection, what is being verified when the technician pulls on the kingpin release handle with the trailer coupled?

That the release cable has adequate slack
That the jaws will open freely in an emergency
That the fifth wheel slide mechanism is functional
That the locking mechanism is fully engaged and cannot be accidentally released (Correct answer)

Correct answer: That the locking mechanism is fully engaged and cannot be accidentally released

Pulling the kingpin release handle while coupled confirms the locking jaws are fully engaged and will not inadvertently release under load.

Question 18: Which measurement is used to verify proper tooth contact pattern during a ring and pinion gear set installation?

Pinion depth with a micrometer
Gear contact pattern using marking compound (Correct answer)
Backlash only, measured at three points
Ring gear runout with a dial indicator

Correct answer: Gear contact pattern using marking compound

Marking compound applied to the ring gear teeth reveals where the pinion contacts the gear, allowing shim adjustments for correct pinion depth and backlash.

Question 19: Thrust angle alignment refers to:

The direction the rear axle(s) push the vehicle compared to the vehicle centerline (Correct answer)
The toe-out angle measured during a turn
The angle between the front axle and the frame
The angle of the steering axis viewed from the front

Correct answer: The direction the rear axle(s) push the vehicle compared to the vehicle centerline

Thrust angle is the direction the rear axle(s) propel the vehicle; if not aligned with the vehicle centerline, the vehicle will dog-track or the steering will be off-center.

Question 20: A hydraulic pump produces adequate flow at low speed but cavitates at high engine RPM. What is the MOST likely cause?

Air trapped in the hydraulic reservoir
Excessive pump output pressure exceeding system rating
A failed pressure relief valve stuck open
A restricted inlet (suction) line or clogged suction strainer (Correct answer)

Correct answer: A restricted inlet (suction) line or clogged suction strainer

Cavitation occurs when the pump cannot draw in enough fluid to fill its displacement chambers, forming vapor bubbles that collapse violently. At low RPM the demand is modest, so a partially restricted suction line is adequate; at high RPM the pump demands more fluid than the restricted line can deliver, causing cavitation. A stuck-open relief valve causes pressure loss, not cavitation. Excessive output pressure damages downstream components. Air in the reservoir contributes but the primary cause of RPM-dependent cavitation is suction restriction.

Question 21: Which type of truck lighting circuit uses a pulse-width modulated (PWM) signal to control brightness?

Hazard flasher circuit
Stop lamp circuit
Marker lamp circuit
Dash dimmer-controlled interior lighting (Correct answer)

Correct answer: Dash dimmer-controlled interior lighting

Dash dimmer controls vary LED or incandescent lamp brightness by modulating the duty cycle of the supply voltage via PWM.

Question 22: A truck coach is equipped with an Allison automatic transmission that repeatedly sets a fault code for 'Turbine Speed Sensor Rationality Error' under load, but clears at idle. The MOST technically accurate explanation is:

The main pressure regulator valve is allowing excessive converter feed pressure that physically deflects the sensor
The turbine speed sensor ground circuit has high resistance causing signal dropout at higher current draw
The torque converter clutch is slipping excessively and falsely triggering the turbine sensor circuit
The turbine speed sensor signal is inconsistent with calculated output shaft speed divided by the current gear ratio under load conditions (Correct answer)

Correct answer: The turbine speed sensor signal is inconsistent with calculated output shaft speed divided by the current gear ratio under load conditions

A rationality error means the TCM has received a plausible but internally inconsistent sensor value — the turbine speed doesn't match what the TCM calculates it should be given the output speed and gear ratio. Under load, torque multiplication in the converter creates higher slip speeds, and if the turbine sensor reads a value that doesn't align with (output shaft speed × gear ratio ± allowable slip), the TCM flags a rationality fault. A slipping TCC would generate a separate slip fault code, a ground resistance issue would cause erratic dropouts across operating conditions, and converter feed pressure does not physically contact the turbine sensor.

Question 23: A technician measures 0.006 inches of clutch brake squeeze clearance on a pull-type clutch during a routine inspection. The OEM specification is 0.125 inches. What is the CORRECT interpretation and immediate consequence of this condition during operation?

The release bearing will contact the pressure plate fingers prematurely, causing clutch chatter during engagement from a stop
The clutch will slip during high-load engagement because the pressure plate cannot achieve full clamping force with insufficient release bearing travel
The clutch brake will drag continuously, slowing the transmission input shaft before complete pedal travel is reached, causing grinding when engaging gear from neutral (Correct answer)
Excessive clutch pedal free play results, preventing the release bearing from contacting the clutch brake entirely

Correct answer: The clutch brake will drag continuously, slowing the transmission input shaft before complete pedal travel is reached, causing grinding when engaging gear from neutral

On a pull-type clutch, the clutch brake is designed to engage during the last 1–2 inches of pedal travel to decelerate the transmission input shaft for clash-free gear engagement from neutral. The 0.006-inch clearance (versus the 0.125-inch spec) means the release bearing is sitting nearly against the clutch brake at rest. Even moderate pedal application will contact and drag the clutch brake well before full disengagement, causing the input shaft to slow prematurely and the clutch brake to wear rapidly. Gear clashing when selecting from neutral is the operational symptom. Insufficient clearance is never a slip or free-play issue — those result from excess clearance.

Question 24: A trailer's tail lights work but the brake lights do not activate. The tractor's brake lights work correctly. Which 7-way trailer connector pin should a technician test first?

Pin 1 (Ground)
Pin 3 (Left turn / Stop) (Correct answer)
Pin 7 (Reverse / Aux)
Pin 4 (Electric Brakes / Battery charge)

Correct answer: Pin 3 (Left turn / Stop)

On the standard SAE J560 7-way connector, Pin 3 carries the left turn/stop signal and Pin 4 carries the right turn/stop signal. Since tail lights (Pin 5 and 6) work but stop lights do not, the brake light signal circuit (Pins 3 and 4) is suspect. Pin 1 is ground — if it were faulty, tail lights would also fail. Pin 7 is reverse/auxiliary. Starting with Pins 3 and/or 4 targets the failed function directly.

Question 25: Which condition found during a battery inspection indicates the battery must be replaced?

Light surface grime on the battery case
Case swelling, a cracked housing, or capacity below 80% on a load test (Correct answer)
Minor terminal corrosion that can be cleaned with baking soda solution
A resting open-circuit voltage of 12.4 volts

Correct answer: Case swelling, a cracked housing, or capacity below 80% on a load test

Physical damage such as swelling or cracking, or a load test result below 80% of rated capacity, indicates the battery cannot reliably deliver adequate power and must be replaced.

Question 26: A 310T technician is evaluating a tractor equipped with an electronically controlled ABS/ATC system. During a loaded brake performance test, the technician observes that the ABS activates on the steer axle at 40 km/h on dry pavement during a moderate brake application that should not exceed 60% of available friction. The wheel speed sensors, tone rings, and wiring check out within spec. What advanced diagnostic step should the technician perform NEXT?

Inspect the steer axle automatic slack adjusters for over-adjustment causing excessive pushrod travel beyond the effective stroke range
Perform a brake chamber stroke measurement at the steer axle to confirm the service brakes are not applying asymmetrically
Replace the ECU, as wheel speed sensor data within spec with ABS activation on dry pavement indicates an internal processing fault
Measure dynamic wheel speed sensor output voltage under vehicle motion to check for tone ring runout-induced signal dropout (Correct answer)

Correct answer: Measure dynamic wheel speed sensor output voltage under vehicle motion to check for tone ring runout-induced signal dropout

Even when a tone ring and sensor pass static ohm and resistance tests, dynamic testing can reveal runout or damage that causes the sensor output to drop below the ECU's signal threshold momentarily at specific wheel speeds. This creates a false wheel deceleration signal (the ECU interprets signal loss as wheel lock-up) and triggers ABS inappropriately. This is a known failure mode on steered axles due to vibration and steering inputs that affect sensor air gap dynamically. Replacing the ECU without dynamic sensor testing would be a costly misdiagnosis. Slack adjuster over-adjustment would cause brake drag or grabbiness, not ABS activation. Asymmetric application would be caught by comparing chamber strokes but would not explain ABS activation at moderate braking.

Question 27: During a pre-trip inspection on a coach with a ZF front air suspension, the technician notices the front ride height is 15mm lower on the left side than the right, but the height control valve has already been replaced. The air supply to both sides measures equal pressure. What is the MOST likely root cause?

A leaking left-side air spring bellows with a slow internal weep
Unequal load distribution due to fuel tank placement
A faulty electronic ride height sensor on the left side
A kinked left-side height control linkage causing the valve to falsely read correct height (Correct answer)

Correct answer: A kinked left-side height control linkage causing the valve to falsely read correct height

If the height control valve has been replaced and air pressure is equal, the most likely cause is a mechanical issue in the valve's sensing linkage. A kinked or binding linkage on the left side causes the valve to sense 'correct height' even when the suspension is low, so the valve never commands the air spring to inflate to proper height. Sensor faults and slow leaks would typically cause continuous corrections or gradual sagging that would be more intermittent.

Question 28: A technician finds a diesel engine with a fuel system that uses a mechanical unit injector (MUI) design. The engine has low power and a misfire on cylinder 5. Adjustment of the injector timing on cylinder 5 to the manufacturer's specification does not resolve the complaint. A cylinder contribution test shows cylinder 5 still low. The injector is replaced with a new unit and retimed — the problem persists. What should the technician investigate NEXT?

The fuel supply pressure to the cylinder head gallery for a restriction
The ECM injector trim files for cylinder 5 for a calibration error
The camshaft lobe for cylinder 5 for abnormal wear or damage (Correct answer)
The rocker arm geometry for excessive side-loading causing injector misalignment

Correct answer: The camshaft lobe for cylinder 5 for abnormal wear or damage

In a mechanical unit injector system, the injector is actuated by the camshaft through a rocker arm — there is no electronic solenoid controlling injection quantity; the cam lobe profile and lift determine injection timing and duration. Replacing the injector and correctly retiming it eliminates the injector and timing adjustment as causes. Since the fault persists with a new, properly timed injector, the mechanical drive mechanism must be at fault. A worn or damaged camshaft lobe on cylinder 5 would reduce injector push-rod travel, decreasing injection quantity and producing the observed low contribution. MUI systems have no ECM trim files for individual injectors.

Question 29: Which of the following best describes the function of a bus bar in a truck's electrical system?

It regulates alternator field current
It stores electrical energy for the starter motor
It distributes power from a common point to multiple circuits (Correct answer)
It converts AC voltage to DC voltage

Correct answer: It distributes power from a common point to multiple circuits

A bus bar is a conductive strip or bar that serves as a central distribution point, supplying power to several branch circuits simultaneously.

Question 30: A technician is inspecting a bus equipped with a Haldex electronic stability control (ESC) system. During a road test, the ESC warning lamp illuminates and a fault code for 'lateral acceleration sensor implausible signal' is stored. The sensor itself tests good when bench-tested. What is the MOST likely root cause to investigate first?

Low system voltage causing ADC conversion errors in the ESC module
A failed yaw rate sensor causing the ECU to reject lateral acceleration data
Incorrect sensor mounting orientation after a recent body repair (Correct answer)
An air leak in the primary service brake circuit affecting ABS modulator function

Correct answer: Incorrect sensor mounting orientation after a recent body repair

Lateral acceleration sensors are orientation-sensitive — they must be mounted exactly as specified (axis perpendicular to vehicle travel, level within tolerance) to produce a valid signal. An 'implausible signal' fault where the sensor itself is confirmed functional strongly suggests the sensor is physically mis-oriented, which commonly occurs after collision repairs where body panels or mounting brackets are replaced or bent. A failed yaw rate sensor generates its own fault code rather than invalidating the lateral accelerometer. Low voltage and brake circuit faults would produce different and more widespread fault codes.

Question 31: A hybrid truck's high-voltage battery management system (BMS) triggers a fault and limits power output. Which parameter does the BMS monitor to protect the battery pack?

Cell voltage, state of charge (SOC), and cell temperature (Correct answer)
Engine coolant temperature and oil pressure
12 V auxiliary battery voltage and alternator output
Transmission fluid temperature and gear position

Correct answer: Cell voltage, state of charge (SOC), and cell temperature

The Battery Management System (BMS) continuously monitors individual cell voltage (to detect over- or under-voltage), state of charge (SOC) to prevent over-discharge or overcharge, and cell temperature (to prevent thermal runaway). When any parameter exceeds safe limits, the BMS reduces or cuts power to protect the pack. Engine oil pressure, transmission temperature, and 12 V charging are managed by separate control modules and are not primary BMS inputs.

Question 32: During a PM inspection of a coach's automatic transmission, the fluid appears dark brown and has a burnt odor. What is the MOST appropriate action?

Note the condition and advise the customer to schedule service within 1,000 miles
Change the fluid and filter, then road test to check for slipping
Add a quart of new fluid to dilute the degraded fluid
Flush the transmission and inspect the torque converter for damage (Correct answer)

Correct answer: Flush the transmission and inspect the torque converter for damage

Dark, burnt transmission fluid indicates severe overheating and potential internal damage, requiring a complete flush and torque converter inspection.

Question 33: What is the function of the torque converter stator?

Redirect fluid from the turbine back to the impeller to multiply torque (Correct answer)
Reduce heat buildup in the converter housing
Control line pressure in the hydraulic circuit
Mechanically lock the impeller to the turbine

Correct answer: Redirect fluid from the turbine back to the impeller to multiply torque

The stator redirects returning fluid from the turbine to assist the impeller, which multiplies torque during low-speed acceleration.

Question 34: A technician hears air leaking from the exhaust port of the brake application valve when brakes are fully released. This indicates:

A worn or damaged graduating spring
A leaking primary or secondary inlet valve seat (Correct answer)
A faulty low-pressure indicator switch
A cracked valve body

Correct answer: A leaking primary or secondary inlet valve seat

A leaking inlet valve seat inside the brake valve allows pressurized reservoir air to pass through the valve and exhaust continuously when brakes are released.

Question 35: What happens to the spring brakes when the parking brake control valve is pushed IN on a truck?

Spring brakes release (Correct answer)
Spring brakes apply
Nothing changes
Service brakes apply

Correct answer: Spring brakes release

Pushing in the parking brake control valve (yellow knob) allows air into the spring brake chambers, compressing the springs and releasing the brakes.

Question 36: A technician is rebuilding a Fuller Ultrashift Plus AMT and notices the low-range synchronizer sleeve has a 0.008" wear step on its inner land but measures 0.003" taper across the cone surface. The OEM specification allows a maximum of 0.005" step and 0.006" taper. What is the CORRECT disposition of this component?

Replace both the sleeve AND the mating synchronizer ring because step wear always indicates ring damage
Reuse the sleeve after polishing the wear step with 400-grit emery cloth to remove the sharp edge
Replace the sleeve — the wear step exceeds the 0.005" limit even though taper is within spec (Correct answer)
Reuse the sleeve — overall average wear is within the combined tolerance of 0.011"

Correct answer: Replace the sleeve — the wear step exceeds the 0.005" limit even though taper is within spec

Transmission component inspection is pass/fail per dimension — you do not average or combine separate tolerances. The sleeve's 0.008" wear step exceeds its individual limit of 0.005", so the part must be replaced regardless of the taper measurement being within specification. Averaging tolerances across different wear modes is not an accepted OEM rebuild practice and could cause synchronization failure under load. Polishing the step would reduce material and alter the geometry beyond spec. Mandatory replacement of the synchronizer ring is not required unless the ring independently fails its own wear check — component condemnation is individual, not cascading by default.

Question 37: What is the primary function of a Variable Geometry Turbocharger (VGT) at low engine speeds?

To open its vanes to maximize exhaust flow and prevent over-speeding
To act as an exhaust brake by creating high backpressure
To close its vanes to increase exhaust gas velocity, improve turbine response, and build boost quickly (Correct answer)
To bypass exhaust gas around the turbine to limit maximum boost pressure

Correct answer: To close its vanes to increase exhaust gas velocity, improve turbine response, and build boost quickly

At low engine speeds, the vanes inside a VGT move to a more closed position, narrowing the passage for exhaust gases. This restriction increases the velocity of the exhaust gas hitting the turbine wheel, causing it to spool up faster and generate boost more quickly, which reduces turbo lag and improves low-end torque.

Question 38: What is a common entry-level position for certified truck and coach technicians?

Maintenance or repair specialist (Correct answer)
Vehicle salesperson
Logistics coordinator
Automotive designer

Correct answer: Maintenance or repair specialist

Certified truck and coach technicians are specifically trained to diagnose, maintain, and repair heavy vehicles. Therefore, their most direct and common entry-level role is in a position focused on these core technical tasks. The certification directly qualifies them for hands-on work in vehicle service centers or transportation companies.

Question 39: A trailer's spring-applied, air-released parking brakes release when the trailer supply line is pressurized, but one axle's brakes do not release fully. What is the MOST likely cause on that axle?

Low air pressure in the trailer reservoir
A leaking trailer brake valve
A seized or corroded spring brake chamber push rod (Correct answer)
A failed glad-hand seal causing air loss

Correct answer: A seized or corroded spring brake chamber push rod

If the air supply is adequate (evidenced by other axles releasing fully), a spring brake chamber that does not release fully indicates a mechanical problem within that chamber — most commonly a seized push rod or corroded brake mechanism that prevents full spring compression. A leaking trailer brake valve would affect all trailer brakes. Low reservoir pressure would affect all axles equally. A failed glad-hand seal would reduce overall supply pressure, again affecting all brakes.

Question 40: While performing a chassis dynamometer test on a turbocharged diesel truck, you observe that boost pressure reaches spec at full throttle but EGT (exhaust gas temperature) is elevated by 120°C above the acceptable limit. Fuel trim and injector balance rates are within range. Which diagnosis is MOST consistent with these findings?

An air-fuel ratio that is excessively lean due to a faulty fuel pressure regulator
A worn turbocharger compressor wheel reducing charge air density
A partially restricted diesel particulate filter increasing exhaust backpressure (Correct answer)
An intercooler core leak reducing charge air temperature below the dew point

Correct answer: A partially restricted diesel particulate filter increasing exhaust backpressure

Elevated EGT with normal boost pressure and injector balance rates points to an exhaust restriction. A partially blocked DPF raises backpressure, forcing exhaust gases to retain heat longer and reducing scavenging efficiency — both elevate EGT significantly. A worn compressor wheel would reduce boost, not leave it at spec. A lean condition would show abnormal fuel trim. An intercooler leak reduces boost pressure and causes white smoke, not elevated EGT with normal boost.

Question 41: A truck driver complains of a steering wheel that pulls to one side only during braking. Which component is MOST likely the cause?

Worn tie rod ends
Loose wheel bearing
Seized or dragging brake caliper on one side (Correct answer)
Worn pitman arm

Correct answer: Seized or dragging brake caliper on one side

A brake caliper that drags on one side creates uneven braking force, pulling the vehicle toward that side only during braking.

Question 42: A truck heater core is leaking coolant into the cab. In addition to replacing the heater core, what else must the technician do?

Flush the cooling system, refill with correct coolant mixture, and check for other leaks (Correct answer)
Replace the entire HVAC box assembly
Replace the thermostat and water pump
Recharge the A/C system with additional refrigerant

Correct answer: Flush the cooling system, refill with correct coolant mixture, and check for other leaks

After replacing a leaking heater core, the system must be flushed to remove any debris or scale, refilled with the correct coolant mixture, and bled of air.

Question 43: In a coach roof-mounted A/C unit, water is dripping into the passenger compartment instead of draining outside. What is the most likely cause?

Overcharged refrigerant system
Faulty condenser fan drawing moisture inside
Cracked evaporator coil
Blocked or frozen evaporator condensate drain (Correct answer)

Correct answer: Blocked or frozen evaporator condensate drain

Condensate from the evaporator normally drains outside through drain tubes; if these are blocked or frozen, water backs up and leaks into the coach interior.

Question 44: If a 310T candidate fails the certification exam, what is the typical minimum waiting period before they may rewrite it?

30 days (Correct answer)
2 weeks
6 months
60 days

Correct answer: 30 days

Most provincial regulators require a minimum 30-day waiting period between exam attempts to allow the candidate time to study and prepare.

Question 45: A technician inflates a truck tire to the maximum pressure stamped on the tire sidewall instead of the pressure specified in the vehicle manufacturer's placard. What is the likely consequence?

Harsh ride, uneven tread wear, and potential overloading of wheel components (Correct answer)
Improved load-carrying capacity and fuel economy
Reduced risk of heat buildup and blowout at highway speeds
Reduced stopping distance due to increased contact patch rigidity

Correct answer: Harsh ride, uneven tread wear, and potential overloading of wheel components

The maximum pressure on the tire sidewall is a structural limit, not a recommended operating pressure. Inflating to the maximum causes the tread center to bulge, concentrating wear in the center, stiffens the sidewall producing a harsh ride, and may subject the wheel, hub, and suspension to higher peak impact loads than they are designed for. The vehicle manufacturer's placard specifies pressures matched to the vehicle's load and suspension — always follow the placard, not the tire's maximum.

Question 46: A technician replaces a dual-circuit foot valve on a Class 8 tractor. After installation, a full-pressure brake application is held for 2 minutes with no leakage, but during a slow, light application the secondary circuit pressure lags the primary circuit by 8–10 psi. What is the MOST probable cause of this pressure differential during light applications?

The secondary circuit supply line has a partial blockage reducing flow velocity
The graduating spring in the secondary piston of the foot valve has incorrect preload (Correct answer)
The secondary delivery check valve is sticking slightly, causing hysteresis in the low-pressure range
An incorrectly torqued secondary circuit delivery port fitting is deflecting the valve body

Correct answer: The graduating spring in the secondary piston of the foot valve has incorrect preload

The dual-circuit foot valve uses stacked pistons with individual graduating springs that control the proportional delivery of pressure to each circuit. If the secondary piston's graduating spring has incorrect preload (due to a faulty replacement part or improper reassembly), it will require more mechanical input force before it begins to open at low pedal effort, causing the secondary circuit to lag during light applications. At full pressure, both circuits eventually equalize, which is why the 2-minute hold test passes. A blockage would cause a flow-dependent lag that worsens at higher flow rates, a sticking check valve is not part of standard dual-circuit valve design, and body deflection from a fitting would be a gross structural issue.

Question 47: When a power divider (interaxle differential) on a tandem axle locks up unexpectedly while driving on a dry road, what is the MOST likely cause?

A stuck or failed air shift actuator in the locked position (Correct answer)
Excessive wear on the spider gears
Low lube level in the forward axle carrier
High mainline air pressure exceeding 120 psi

Correct answer: A stuck or failed air shift actuator in the locked position

A stuck pneumatic actuator can mechanically lock the power divider in the engaged position, creating driveline bind on dry pavement.

Question 48: On a common rail diesel fuel system, what component maintains system pressure between injection events?

Injection control pressure sensor
Fuel pressure regulator valve
Fuel lift pump
High-pressure accumulator rail (Correct answer)

Correct answer: High-pressure accumulator rail

The high-pressure accumulator rail stores pressurized fuel and dampens pressure fluctuations to maintain consistent injection pressure.

Question 49: A technician is diagnosing a no-start condition on a diesel. Fuel pressure is correct but the engine will not start. What should be checked next?

Alternator output voltage
Power steering fluid level
Engine oil level
Glow plug or grid heater operation (Correct answer)

Correct answer: Glow plug or grid heater operation

If fuel pressure is adequate and the engine won't start in cold or normal conditions, faulty glow plugs or a grid heater are a primary suspect for diesels.

Question 50: What is the correct procedure for checking lubricant level in a standard drive axle while the vehicle is on level ground?

Remove the fill plug; lubricant should be at or slightly below the fill hole (Correct answer)
Check via the breather vent on top of the housing
Remove the drain plug and check for flow
Remove the inspection cover and measure with a dipstick

Correct answer: Remove the fill plug; lubricant should be at or slightly below the fill hole

The fill hole doubles as the level indicator; if lubricant drips out when the plug is removed, the level is correct.

Question 51: A heavy-duty truck with a manual transmission is difficult to shift into any gear when the engine is running but shifts freely when the engine is off. The MOST likely cause is:

Low transmission oil level
Worn transmission synchronizers
Clutch not fully releasing (dragging clutch) (Correct answer)
Bent shift forks

Correct answer: Clutch not fully releasing (dragging clutch)

A dragging clutch keeps the input shaft spinning even when pedal is fully depressed, making synchronization difficult and grinding gears.

Question 52: When recovering refrigerant from a 310T-compliant truck A/C system, the technician must:

Only recover refrigerant if the system pressure exceeds 200 psi
Use EPA-certified recovery equipment and store refrigerant in approved containers (Correct answer)
Vent the refrigerant outside the shop
Mix recovered refrigerant with new refrigerant before reuse

Correct answer: Use EPA-certified recovery equipment and store refrigerant in approved containers

EPA Section 608 regulations require certified recovery equipment and approved containers when servicing any stationary or mobile A/C system.

Question 53: Which type of refrigerant oil is specified by most manufacturers for use in heavy-duty truck A/C systems charged with R-134a?

Alkylbenzene Oil
PAG (Polyalkylene Glycol) Oil (Correct answer)
Mineral Oil
POE (Polyol Ester) Oil

Correct answer: PAG (Polyalkylene Glycol) Oil

PAG (Polyalkylene Glycol) oil is the lubricant most commonly specified for use in mobile A/C systems with R-134a refrigerant. Mineral oil is not miscible with R-134a and will not circulate properly, leading to compressor failure. POE oil is often used for retrofits or in electric/hybrid vehicles but PAG is the standard for conventional R-134a systems.

Question 54: A journeyperson 310T technician from British Columbia relocates to Ontario and presents their Interprovincial (Red Seal) Certificate. Which step is STILL required before they can legally work as a 310T technician in Ontario?

No additional steps are required; the Red Seal certificate is recognized in all provinces including Ontario without further process
They must complete a 500-hour Ontario-specific supervised work period before independent licensure
They must rewrite the full Ontario 310T examination within 6 months of establishing residency
They must apply to Ontario's Ministry of Labour, Immigration, Training and Skills Development and obtain an Ontario Certificate of Qualification, as provincial registration is still required (Correct answer)

Correct answer: They must apply to Ontario's Ministry of Labour, Immigration, Training and Skills Development and obtain an Ontario Certificate of Qualification, as provincial registration is still required

While the Red Seal endorsement allows a tradesperson to work in participating provinces without re-examination, in Ontario a tradesperson must still register their credential with the provincial authority (formerly OCOT, now the Ministry) to obtain an Ontario Certificate of Qualification. The Red Seal facilitates recognition but does not automatically create the provincial credential — an administrative registration step is required.

Question 55: When inspecting a hydraulic cylinder that is leaking past the rod seal, a technician notices the rod surface has a spiral groove worn into it. What caused this damage?

Over-pressurization of the cylinder
Excessive extension speed causing hydraulic hammer
Contaminated hydraulic fluid containing abrasive particles (Correct answer)
Incorrect rod material for the application

Correct answer: Contaminated hydraulic fluid containing abrasive particles

A spiral groove on a hydraulic rod is a classic signature of abrasive contamination in the fluid. Dirt or metal particles caught between the rod and wiper/seal rotate as the rod travels, cutting a helical pattern. Over-pressurization causes seal extrusion, not spiral scoring; incorrect material would cause uniform corrosion or pitting; hydraulic hammer damages end caps and hoses, not the rod surface in a spiral pattern.

Question 56: What is the primary purpose of a diesel engine's unit injector (UI) system compared to a common rail system?

Unit injectors use lower injection pressures for better atomization
Unit injectors are controlled mechanically without ECM input
Unit injectors allow multiple injection events per cycle more easily
Each unit injector generates its own high pressure, eliminating a separate high-pressure pump (Correct answer)

Correct answer: Each unit injector generates its own high pressure, eliminating a separate high-pressure pump

In a unit injector system, the injector itself generates high pressure via a rocker-arm-driven plunger, unlike common rail which uses a central pump.

Question 57: While diagnosing an ABS modulator valve, you cycle the valve electrically and observe correct inlet solenoid function (holds pressure) but the exhaust solenoid fails to vent the chamber quickly enough, resulting in a 300ms longer release than specification. The solenoid resistance measures 6.2 ohms (spec: 5.5–7.0 ohms). What is the MOST likely cause of the slow exhaust?

Electrical resistance too high, causing insufficient current to fully open the exhaust solenoid plunger
A contaminated or partially blocked exhaust port orifice in the modulator valve body (Correct answer)
A failing wheel speed sensor providing incorrect speed data and causing premature exhaust solenoid activation
Incorrect supply voltage to the ABS ECU causing reduced solenoid drive duty cycle

Correct answer: A contaminated or partially blocked exhaust port orifice in the modulator valve body

Since the solenoid coil resistance is within the 5.5–7.0 ohm specification, the electrical side of the exhaust solenoid is functioning correctly. Slow exhaust despite a properly energized solenoid points to a mechanical restriction — specifically a contaminated or partially blocked exhaust port orifice. Desiccant debris, oil contamination from compressor ring blow-by, or ice formation can partially block the small exhaust orifice, slowing chamber depressurization without triggering an electrical fault code. A wheel speed sensor issue would cause different fault patterns, not a repeatable slow exhaust on bench cycle testing.

Question 58: When performing a brake chamber stroke check on a service brake, the pushrod stroke must not exceed which limit to pass inspection?

50% of the chamber's rated stroke
2 inches regardless of chamber size
The maximum stroke marked on the chamber
The readjustment limit specified by FMCSA (Correct answer)

Correct answer: The readjustment limit specified by FMCSA

FMCSA regulations define readjustment limits for each brake chamber size, and a stroke exceeding that limit requires immediate adjustment.

Question 59: A technician is setting front toe on a Class 8 truck. After adjustment, the toe should be verified with the vehicle:

On a flat, level surface with the vehicle at proper ride height and steering centered (Correct answer)
On a turn plate with the steering at full lock
On a drive-on lift with wheels hanging
With the engine running to simulate road load

Correct answer: On a flat, level surface with the vehicle at proper ride height and steering centered

Toe must be set with the vehicle at proper ride height on a flat surface and the steering centered to reflect actual operating conditions.

Question 60: According to Canadian federal regulations, what is the mandatory procedure a technician must follow before opening an A/C system containing HFC refrigerants like R-134a for service?

Use certified recovery equipment to capture the refrigerant. (Correct answer)
Vent the refrigerant slowly into a container of oil.
Neutralize the refrigerant with an approved chemical agent.
Flush the system with nitrogen to purge the refrigerant.

Correct answer: Use certified recovery equipment to capture the refrigerant.

Federal and provincial regulations in Canada mandate that HFC refrigerants, which have high global warming potential, must not be knowingly vented to the atmosphere. Technicians are required to use certified recovery and recycling equipment to safely remove and store the refrigerant before servicing the system.

Question 61: On a tractor-trailer combination, maximum pressure drop during a combined leakage test with brakes applied must not exceed:

6 psi per minute (Correct answer)
4 psi per minute
3 psi per minute
8 psi per minute

Correct answer: 6 psi per minute

FMCSA regulations allow up to 6 psi per minute pressure drop for combination vehicles during a static leakage test with service brakes applied.

Question 62: Which color is universally used on hybrid and electric trucks to identify high-voltage cables and components?

Red
Yellow
Blue
Orange (Correct answer)

Correct answer: Orange

SAE J1673 and vehicle OEM standards specify orange as the identifier for high-voltage (60–1000 V DC or AC) wiring in hybrid and electric vehicles, including trucks and coaches. Red is used for positive low-voltage wiring. Yellow is used in some safety contexts (e.g., airbag wiring) but not HV. Blue is sometimes used for 12 V auxiliary systems. Recognizing orange cables is a basic EV safety requirement for any technician working on these vehicles.

Question 63: Which diesel engine emission control system recirculates exhaust gases back into the intake to reduce NOx emissions?

Exhaust Gas Recirculation (EGR) (Correct answer)
Selective Catalytic Reduction (SCR)
Diesel Oxidation Catalyst (DOC)
Diesel Particulate Filter (DPF)

Correct answer: Exhaust Gas Recirculation (EGR)

EGR reduces peak combustion temperatures by diluting the intake charge with inert exhaust gas, which lowers the formation of NOx.

Question 64: A truck with an Eaton Fuller 18-speed transmission exhibits gear clash specifically when shifting from 5th to 6th gear under load at highway speeds, but shifts smoothly during all other gear changes. The clutch brake engages properly and the clutch adjustment is within spec. What is the MOST likely root cause?

Air leak in the range cylinder causing incomplete high-range engagement
Worn mainshaft 6th gear clutching teeth
Faulty range valve causing delayed auxiliary section preselection (Correct answer)
Worn synchronizer blocking ring for the auxiliary section range shift

Correct answer: Faulty range valve causing delayed auxiliary section preselection

In an Eaton Fuller 18-speed, the range shift (low to high auxiliary) must be preselected before completing the main box shift into 6th. A faulty range valve delays the auxiliary section air signal, causing the auxiliary to still be in low range when the driver completes the main box shift into 6th — creating clash at that specific transition. If clutching teeth or synchronizers were worn, the problem would appear across multiple gears, not just the 5th-to-6th transition.

Question 65: A Red Seal-endorsed 310T technician relocating from Ontario to British Columbia discovers that BC uses the trade classification 'Commercial Transport Mechanic' (CTM). Which statement most accurately describes their inter-provincial recognition pathway?

They are required to pass a provincial equivalency exam and complete a minimum 500-hour provincial top-up before receiving a BC certificate
Their Red Seal endorsement grants automatic recognition under the Interprovincial Standards Program, allowing them to challenge the BC CTM exam without serving additional hours (Correct answer)
Red Seal recognition applies only within Atlantic Canada and Quebec; western provinces require separate bilateral agreements
They must complete a full CTM apprenticeship program in BC before being permitted to work in the trade

Correct answer: Their Red Seal endorsement grants automatic recognition under the Interprovincial Standards Program, allowing them to challenge the BC CTM exam without serving additional hours

The Red Seal (Interprovincial Standards Program) exists precisely to enable labour mobility. A holder of a Red Seal-endorsed 310T certificate can present that endorsement to the BC Industry Training Authority and receive recognition as a qualified CTM without repeating apprenticeship hours or sitting a separate provincial exam. This is a core career-mobility benefit of pursuing the Red Seal beyond the provincial certificate.

Question 66: Before working on the high-voltage system of a hybrid truck, a technician must de-energize the system. What is the FIRST step after donning appropriate PPE?

Discharge the HV capacitors using a load resistor connected to the DC bus
Remove the high-voltage service disconnect (manual service disconnect) plug (Correct answer)
Disconnect the 12 V auxiliary battery negative cable
Cut the orange high-voltage cables to isolate the circuit

Correct answer: Remove the high-voltage service disconnect (manual service disconnect) plug

The correct sequence requires removing the high-voltage manual service disconnect (MSD) plug first — this physically breaks the HV circuit and isolates the battery pack from the rest of the system. After removing the MSD, the technician waits the manufacturer-specified time for capacitor discharge before measuring residual voltage. Disconnecting the 12 V battery first is done in some procedures but does not isolate the HV bus. Cutting orange cables is extremely dangerous and never a service procedure. Capacitor discharge via external load is performed only after the MSD is removed, not before.

Question 67: A technician is measuring driveshaft phasing on a truck with a two-piece driveshaft using a double-Cardan constant-velocity joint at the front. The rear U-joint of the front shaft measures 3° operating angle. What operating angle should the technician aim for at the rear U-joint of the rear shaft to minimize torsional vibration?

1.5° — half the front angle to progressively reduce angular velocity fluctuation
0° — the double-Cardan joint at the front already provides CV output, so the rear joint should be parallel
6° — double the front angle to compensate for the CV joint's velocity smoothing effect
3° — equal and opposite cancellation requires matching angles on the output end of the rear shaft (Correct answer)

Correct answer: 3° — equal and opposite cancellation requires matching angles on the output end of the rear shaft

Standard U-joint cancellation theory requires that the operating angles at both ends of a driveshaft be equal, with the yokes in phase, so that the velocity acceleration/deceleration introduced by the front joint is exactly cancelled by the rear joint. On the rear shaft of a two-piece arrangement, the same principle applies: the front and rear joints of that shaft must have equal operating angles. The double-Cardan joint on the front half-shaft produces a true CV (constant velocity) output, which means the rear shaft receives smooth input — the rear shaft's own joints must still be equal-and-opposite to each other (3° = 3°). The double-Cardan does not alter the requirement for the rear shaft's own joint cancellation.

Question 68: A natural gas (CNG) coach engine misfires intermittently at operating temperature but runs smoothly when cold. No fault codes are stored. Fuel system pressure at the regulator outlet is stable. Which diagnostic step would MOST directly isolate a temperature-dependent fuel delivery fault?

Inspect and pressure-test the CNG storage cylinders for rated capacity at ambient temperature
Test the high-pressure lock-off solenoid for current draw and coil resistance at ambient temperature
Perform a cylinder balance test cold and compare contribution values to a hot retest (Correct answer)
Monitor fuel rail pressure with a scan tool during a hot misfire event to detect momentary pressure drops

Correct answer: Perform a cylinder balance test cold and compare contribution values to a hot retest

Because the fault is temperature-dependent and intermittent with no stored codes, the goal is to capture data during the actual fault condition. Performing a cylinder balance (contribution) test when cold and then repeating it once the engine is at operating temperature and misfiring directly compares each cylinder's contribution in both states, pinpointing which cylinder(s) degrade with heat. This could indicate a thermally expanding component (valve, injector seat) or a sensor drifting with heat. Static tests at ambient temperature will not reproduce a hot-only fault.

Question 69: A truck equipped with a Selective Catalytic Reduction (SCR) system is experiencing increased Diesel Exhaust Fluid (DEF) consumption and has an active P20EE fault code. What is the MOST likely cause of this issue?

A clogged Diesel Particulate Filter (DPF)
A failing turbocharger actuator
A malfunctioning upstream NOx sensor (Correct answer)
Low-quality or contaminated DEF

Correct answer: A malfunctioning upstream NOx sensor

The P20EE code indicates that the SCR catalyst efficiency is below the required threshold. The aftertreatment control module monitors NOx levels using both upstream (engine-out) and downstream (tailpipe-out) NOx sensors. If the upstream NOx sensor provides inaccurately high readings, the system will inject an excessive amount of DEF to compensate, leading to increased consumption and eventually triggering an efficiency code when the downstream sensor does not report the expected reduction in NOx.

Question 70: Which of the following wheel alignment angles has the primary responsibility for creating directional stability and promoting steering wheel returnability after a turn?

Thrust Angle
Caster (Correct answer)
Toe
Camber

Correct answer: Caster

Caster is the forward or rearward tilt of the steering axis when viewed from the side. A positive caster angle positions the tire's contact patch behind the steering axis pivot, creating a self-aligning torque that helps the vehicle maintain a straight path and causes the steering wheel to return to center.

Question 71: When replacing a truck's battery in a system with multiple electronic control modules, what precaution is MOST important before disconnecting the battery?

Warm up the engine to operating temperature
Discharge the battery to zero volts first
Remove all fuses from the fuse panel
Connect a memory saver or secondary power supply to maintain module power (Correct answer)

Correct answer: Connect a memory saver or secondary power supply to maintain module power

Many truck ECMs store volatile calibration data, adaptive strategies, and security codes in RAM; a memory saver preserves this data during battery replacement.

Question 72: What does a hydraulic system relief valve do when system pressure reaches its set point?

It shuts off the pump motor to prevent over-pressurization
It closes the main control valve to stop cylinder movement
It opens a secondary circuit to share load with another pump
It bypasses excess fluid back to the reservoir to limit maximum system pressure (Correct answer)

Correct answer: It bypasses excess fluid back to the reservoir to limit maximum system pressure

A relief valve is a pressure-limiting safety device: when system pressure hits the set point, the valve opens and diverts fluid back to the reservoir (tank), holding pressure at the maximum set value without damaging components. It does not stop the pump motor, engage a secondary circuit, or close control valves — those are functions of separate components.

Question 73: A heavy truck's front axle service brakes apply fully when the trailer brake hand valve is actuated, but the trailer brakes do not respond. The trailer's supply line shows 120 psi. Which component failure MOST specifically explains this symptom pattern?

A blocked or closed trailer service (control) line preventing signal pressure from reaching the trailer relay valve (Correct answer)
A seized relay valve on the trailer causing no delivery pressure to the service chambers
A failed trailer control valve (hand valve) delivering signal only to the tractor circuit
A defective double-check valve in the tractor causing primary circuit to back-feed the hand valve signal

Correct answer: A blocked or closed trailer service (control) line preventing signal pressure from reaching the trailer relay valve

The trailer supply line is pressurized at 120 psi, confirming the glad hand connection and supply path are intact. The hand valve actuating the front tractor brakes confirms the hand valve is sending signal pressure — but only to the tractor circuit, not the trailer. The trailer service (control) line carries the application signal from the hand valve to the trailer relay valve. A blocked or disconnected control line means the trailer relay valve never receives the signal to apply, even though supply air is present. A seized relay valve would prevent application but would not explain why tractor brakes fire.

Question 74: What is checked during a slack adjuster inspection on an S-cam drum brake system?

Brake pedal travel height
Brake fluid reservoir level
Adjustment arm travel distance and proper manual or automatic adjustment function (Correct answer)
Air compressor output pressure

Correct answer: Adjustment arm travel distance and proper manual or automatic adjustment function

Slack adjusters control the stroke of the brake chamber push rod; verifying arm travel and correct auto-adjustment confirms brakes will apply within the allowable stroke limit.

Question 75: A diesel technician is diagnosing an intermittent DTC for a high-pressure fuel rail pressure deviation on a common-rail engine. Fuel pressure holds steady at idle but drops 18 MPa below commanded pressure during a snap throttle event. The high-pressure pump and injectors have been verified as serviceable. What is the MOST likely root cause?

Worn injector return springs allowing excessive back-leak volume at peak load
An ECM calibration fault requiring a software reflash to update the fuel-demand map
A faulty fuel rail pressure sensor reporting falsely low values under vibration
A partially restricted fuel supply line causing cavitation at the high-pressure pump inlet during demand surges (Correct answer)

Correct answer: A partially restricted fuel supply line causing cavitation at the high-pressure pump inlet during demand surges

When the high-pressure pump and injectors are confirmed good, the next logical suspect under surge conditions is a restriction on the low-pressure (supply) side. A partially blocked pre-filter, kinked supply line, or failing lift pump causes inlet cavitation when demand spikes, starving the high-pressure pump. The pressure drop only during snap-throttle events is a classic starvation symptom. A sensor fault would present at idle too; an ECM reflash does not address a mechanical limitation; and injector back-leak would show at idle as well.

Question 76: A technician is diagnosing an ABS fault on a trailer where wheel speed sensor signal is intermittent on one axle end. The resistance across the sensor measures 1,050 ohms — within spec. The air gap is correct. The fault only occurs when the vehicle is moving over rough road surfaces. What is the MOST likely cause?

A deteriorated exciter ring with missing or damaged teeth causing erratic signal dropout
Excessive bearing end-play allowing the exciter ring to move laterally and vary the air gap dynamically (Correct answer)
Corroded sensor connector pins causing intermittent open circuit only under vibration
A faulty ABS ECU unable to process high-frequency signals at speed

Correct answer: Excessive bearing end-play allowing the exciter ring to move laterally and vary the air gap dynamically

Excessive bearing end-play is the classic cause of a vibration-induced intermittent wheel speed sensor fault where static measurements (resistance, static air gap) all pass. As the bearing moves laterally on rough surfaces, the exciter ring shifts in and out of optimal range, causing signal dropouts. The sensor resistance and static air gap are fine, ruling out sensor damage or exciter ring tooth damage. Connector corrosion typically causes a measurable resistance increase rather than only vibration-induced drops.

Question 77: A 310T candidate is asked to explain the function of the inversion valve in a tractor protection system. Which statement MOST accurately describes the inversion valve's operation during a trailer supply line failure?

It diverts primary circuit air pressure to the trailer emergency line to maintain braking until the driver manually sets the parking brake
It inverts the signal pressure from the trailer supply line to apply the tractor spring brakes proportionally as trailer supply pressure falls
It uses the loss of trailer supply line pressure as a signal to release a pilot port, allowing spring brake hold-off pressure to exhaust and setting the tractor spring brakes (Correct answer)
It closes the trailer supply line to prevent back-flow of air from the tractor primary circuit into the failed trailer circuit

Correct answer: It uses the loss of trailer supply line pressure as a signal to release a pilot port, allowing spring brake hold-off pressure to exhaust and setting the tractor spring brakes

The inversion valve (also called the spring brake control valve in some configurations) operates on an inverse logic principle: it uses supply pressure at its signal port to hold the spring brake release line open. When the trailer supply line fails or pressure drops below approximately 45 psi, the signal pressure at the inversion valve's pilot port drops, causing the valve to shift and exhaust the spring brake hold-off air, setting the tractor spring brakes automatically. This is 'inverted' because the valve acts when pressure is lost, not when it is applied. It does not proportionally apply spring brakes, does not prevent back-flow (that is the trailer supply valve's function), and does not divert primary circuit air to the trailer.

Question 78: During a pre-trip inspection, a driver notices excessive vertical (up-and-down) play when trying to move the pitman arm. What is the MOST probable cause of this movement?

Loose wheel bearings.
Worn steering gear sector shaft splines or a loose pitman arm retaining nut. (Correct answer)
Worn tie-rod ends.
Normal operation of the steering linkage.

Correct answer: Worn steering gear sector shaft splines or a loose pitman arm retaining nut.

The Pitman arm is splined to the steering gear's sector shaft and should only move in a rotational arc. Any significant up-and-down (vertical) movement indicates that the connection between the Pitman arm and the sector shaft is loose. This could be due to worn splines on either component or a retaining nut that has backed off, which is a severe safety concern.

Question 79: A truck cab window fogs repeatedly on the inside despite the defroster being on. What is the most likely HVAC-related cause?

Blocked evaporator drain tube
A leaking heater core introducing moisture into the cabin airstream (Correct answer)
Excessively cold outside air entering the cab
Overcharged A/C system

Correct answer: A leaking heater core introducing moisture into the cabin airstream

A leaking heater core introduces coolant steam into the cabin, significantly increasing humidity and causing persistent interior fogging that defrosting alone cannot overcome.

Question 80: When performing a brake balance test on a three-axle transit coach using an electronic brake force meter, the technician finds the rear tag axle produces 18% less retardation force than the drive axle at the same applied pressure. After confirming lining thickness and drum diameter are within spec on all axles, what is the MOST likely root cause?

Unequal brake chamber sizes between the drive and tag axles creating a force imbalance (Correct answer)
A partially restricted delivery port in the rear axle limiting valve reducing pressure to the tag axle chambers
A misadjusted proportioning valve biasing pressure away from the rear axle group
Contaminated brake lining on the tag axle reducing the coefficient of friction

Correct answer: Unequal brake chamber sizes between the drive and tag axles creating a force imbalance

When lining and drum specs are confirmed equal, force imbalance at identical line pressure points directly to a mechanical output difference — most commonly unequal brake chamber sizes. A larger chamber produces greater actuator force at the same pressure. Transit coaches often use different chamber types across axles, and a type 24 versus type 30 chamber would produce this measurable retardation difference. A limiting valve restriction would be detectable with a test gauge; contaminated lining was ruled out by the spec confirmation; and a proportioning valve would affect both axles in the rear group equally.

Question 81: During a diesel high-pressure common rail (HPCR) system diagnosis, a technician finds that fuel trim data shows a large positive correction on cylinders 3 and 4 only. Cylinder contribution tests confirm low power from these cylinders. Injector return-leak tests show cylinders 3 and 4 have significantly LOWER return flow than the others. What is the MOST accurate interpretation?

Air in the fuel supply is preferentially affecting the higher-numbered injectors
Injectors 3 and 4 have stuck-open control valves causing excessive return leak
Injectors 3 and 4 have worn nozzle tips causing restricted fuel delivery (Correct answer)
The high-pressure pump is losing prime, affecting only the rear cylinders

Correct answer: Injectors 3 and 4 have worn nozzle tips causing restricted fuel delivery

In HPCR systems, low return flow from an injector indicates it is not leaking internally — the control valve is holding. However, combined with low cylinder contribution and a positive fuel trim correction on those cylinders, this points to restricted nozzle orifices (worn or partially clogged tips) that limit the actual fuel mass injected despite the ECM commanding more fuel. High return flow would indicate a leaking control valve. The pump affects rail pressure globally, not cylinder-selectively.

Question 82: A technician is installing a new ECM on a heavy-duty truck. After installation, the engine will not start. The MOST likely reason is:

The fuel pump relay is faulty
The replacement ECM requires programming or key-matching to the vehicle (Correct answer)
The battery voltage is too high
The ECM is not properly grounded

Correct answer: The replacement ECM requires programming or key-matching to the vehicle

Most modern truck ECMs must be programmed with the vehicle's VIN, engine calibration, and security parameters before the engine will start.

Question 83: A diesel engine on a Class 8 truck exhibits black smoke under load but clears at idle. Fuel pressure and injector return flow tests are within spec. A compression test shows all cylinders within 10% of each other. Which condition is MOST likely causing this symptom?

A restricted charge air cooler reducing boost density at high load (Correct answer)
A faulty fuel pressure regulator allowing excess fuel delivery at idle
A cracked cylinder head causing intermittent coolant intrusion into combustion
Worn piston rings allowing blow-by only at elevated cylinder pressures

Correct answer: A restricted charge air cooler reducing boost density at high load

Black smoke under load that clears at idle indicates a rich air-fuel ratio specifically when demand is high. A restricted charge air cooler (CAC/intercooler) reduces the density and volume of intake air reaching the cylinders under boost conditions, creating a fuel-rich mixture and black smoke. Compression is acceptable, injectors are fine, and the symptom being load-dependent points to the air-supply side, not fuel-side over-delivery.

Question 84: What is the function of the king pin inclination (KPI) angle?

Sets the amount of steering wheel return after a turn
Provides directional stability by creating a self-centering effect and reducing steering effort (Correct answer)
Controls the maximum steering lock angle
Determines the amount of toe change during suspension travel

Correct answer: Provides directional stability by creating a self-centering effect and reducing steering effort

KPI creates a geometric pivot that causes the front of the vehicle to lift slightly in a turn, providing a self-centering force and reducing steering effort.

Question 85: A vehicle equipped with an automatic transmission exhibits abnormal noise only in Park and Neutral but not in Drive or Reverse. The MOST likely cause is:

Worn output shaft bearing
Worn or damaged torque converter pilot hub or front pump bushing (Correct answer)
Excessive rear band adjustment
Failed 1st-clutch pack

Correct answer: Worn or damaged torque converter pilot hub or front pump bushing

In Park and Neutral the torque converter spins with no load on the gear train; noise isolated to these ranges points to the front pump or converter hub interface.

Question 86: What does a resistor in series with a trailer marker lamp circuit indicate when used in a conventional (non-LED) hookup?

It simulates the load of a burned-out lamp to prevent false turn-signal hyper-flash (Correct answer)
It protects the BCM output from overload
It filters electromagnetic interference from the circuit
It reduces voltage to prevent lamp burnout

Correct answer: It simulates the load of a burned-out lamp to prevent false turn-signal hyper-flash

When LED trailer lamps replace incandescent lamps, load resistors are added to mimic the higher current draw so the truck's flasher unit maintains the correct flash rate.

Question 87: A heavy-duty diesel uses a Variable Geometry Turbocharger (VGT). The engine produces low power and excessive black smoke. Boost pressure reaches only 18 psi under full load where 28 psi is expected. The VGT actuator moves freely across its full range when commanded by a scan tool. Exhaust backpressure measured upstream of the turbocharger is within specification. What is the MOST likely root cause?

A worn compressor wheel with excessive tip clearance reducing compression efficiency
A cracked turbine housing causing exhaust gas bypass around the turbine wheel
A faulty MAP sensor reporting false-high boost, causing the ECM to reduce fueling
Sticking VGT vanes that are mechanically seized in the high-flow (low-boost) position despite actuator movement (Correct answer)

Correct answer: Sticking VGT vanes that are mechanically seized in the high-flow (low-boost) position despite actuator movement

The VGT actuator rod moves freely when commanded in isolation, but this does not confirm the vanes inside the turbine housing are actually responding. Carbon and soot buildup commonly seizes the variable vanes in the open (high-flow, low-boost) position. The actuator mechanism can move but if the linkage is disconnected or the vanes are seized, boost won't build. Exhaust backpressure being normal rules out a downstream blockage. A cracked housing would typically produce audible leaks and codes. A MAP sensor fault would trigger a code. Compressor wear would show consistent low boost across all conditions, not a dramatic deficit.

Question 88: A coach technician is diagnosing a steering pull that only occurs during moderate to hard braking. Steering geometry, tire pressure, and brake adjustment are all within spec. What is the MOST probable cause?

Loose steering gear mounting bolts deflecting the gear under braking G-force
Excessive positive camber on one side overpowering the self-centering torque
Unequal front brake torque creating asymmetric deceleration loading on the steering linkage
Worn drag link center socket allowing horizontal lash under longitudinal load (Correct answer)

Correct answer: Worn drag link center socket allowing horizontal lash under longitudinal load

A worn drag link center socket (the internal socket at mid-span or at the steering gear arm end) can have acceptable static lash but exhibit significant lash under the longitudinal deceleration forces generated during braking. As weight shifts forward and the steering geometry loads up, the worn socket allows the drag link to deflect, steering the front axle and producing a pull that disappears when braking ends. Brake torque asymmetry would show up in brake adjustment checks. Gear mount bolts typically cause wander or play, not a load-specific pull. Camber affects steady-state pull, not a braking-triggered pull.

Question 89: What is the correct procedure when replacing a U-joint to prevent bearing cup damage during installation?

Press the bearing cups in simultaneously using an arbor press (Correct answer)
Drive cups in with a hammer and punch sequentially
Heat the yoke ears to expand them before pressing
Use only snap rings on one side of each yoke ear

Correct answer: Press the bearing cups in simultaneously using an arbor press

Using an arbor press to install both bearing cups simultaneously keeps the cross centered and prevents skewing the needle bearings.

Question 90: What type of lubricant is typically specified for steering knuckle king pin bushings during chassis lubrication?

Silicone spray lubricant
NLGI No. 2 multi-purpose lithium complex grease (Correct answer)
Gear oil 80W-90
Engine oil

Correct answer: NLGI No. 2 multi-purpose lithium complex grease

NLGI No. 2 lithium complex grease provides the correct consistency and extreme-pressure protection required for high-load suspension and steering pivot points.

Question 91: During a cylinder contribution test on a 6-cylinder diesel, RPM drop for cylinder 4 is significantly less than the others, suggesting low contribution. Compression and injector leak-down both test normal. Fuel trim data shows the ECM is commanding increased fueling to cylinder 4. A fuel sample from the return line of injector 4 shows higher-than-normal return volume. What is the MOST likely root cause?

A cracked injector body is allowing fuel to leak externally without entering the combustion chamber
The cylinder 4 glow plug is drawing excessive current, causing heat-related misfiring
The injector is hydraulically stuck open, dumping fuel continuously into the cylinder
The injector needle control valve is worn, causing early needle lift and reduced effective injection pressure, with excess fuel bypassing to return (Correct answer)

Correct answer: The injector needle control valve is worn, causing early needle lift and reduced effective injection pressure, with excess fuel bypassing to return

High return fuel volume from a specific injector with normal compression and leak-down (static tests) but low cylinder contribution points to a worn needle control valve. This wear allows the needle to lift at lower injection pressures than designed, reducing the effective spray-in pressure and atomization. Much of the commanded fuel bypasses past the worn control valve and returns to the tank without contributing to combustion. The ECM compensates by commanding more fuel, but efficiency drops because delivery pressure is compromised. A cracked body would show external leakage. A stuck-open injector would cause severe wet fouling and smoking, not just low contribution.

Question 92: Under FMCSA regulations, what defines an 'out-of-service' condition for a commercial motor vehicle?

A vehicle that has exceeded its PM interval by 500 miles
A defect so severe that continued operation poses an imminent hazard to safety (Correct answer)
A vehicle carrying more than half its rated payload
Any defect identified during a roadside inspection

Correct answer: A defect so severe that continued operation poses an imminent hazard to safety

An out-of-service order is issued when a defect creates an imminent safety hazard; the vehicle must not be operated until the defect is corrected.

Question 93: A technician is performing a failure analysis on a heavy-duty inter-axle differential that has suffered ring-and-pinion failure. The wear pattern on the failed ring gear shows concentrated contact across the full face width but only on the toe end of the gear tooth. What does this pattern indicate about the differential's pre-failure condition?

The ring gear backlash was set too tight, forcing full face contact under thermal expansion
Insufficient pinion preload, allowing the pinion to deflect away from the ring gear under load
The pinion was set too shallow (pinion is too far from the ring gear centerline) (Correct answer)
Excessive pinion depth setting, causing the pinion to sit too deep in the housing

Correct answer: The pinion was set too shallow (pinion is too far from the ring gear centerline)

In ring-and-pinion gear analysis, 'toe' refers to the small end of the gear tooth (near the center of the ring gear). A contact pattern concentrated at the toe indicates the pinion is positioned too far away from the ring gear — i.e., the pinion depth is shallow. This causes the mesh to occur at the narrow end of the hypoid tooth rather than the ideal center, concentrating stress and leading to fatigue failure. A deep pinion setting would shift contact toward the heel (large end). This distinction is fundamental to final drive diagnosis.

Question 94: When replacing a heavy-duty clutch assembly, the flywheel face and pressure plate mating surface should be inspected for:

Correct magnetic flux density
Thread condition on mounting bolts only
Hot spots, heat cracks, grooves, and flatness (Correct answer)
Surface hardness using a Rockwell tester

Correct answer: Hot spots, heat cracks, grooves, and flatness

Hot spots, cracks, grooves, and warpage on the flywheel or pressure plate cause uneven clamp load and premature clutch disc wear.

Question 95: On a tandem-axle suspension, what is the main purpose of longitudinal and transverse torque rods?

To control axle positioning and absorb braking and acceleration forces. (Correct answer)
To absorb road vibrations for a smoother ride.
To support the vertical load of the vehicle.
To provide a mounting point for the air springs.

Correct answer: To control axle positioning and absorb braking and acceleration forces.

Torque rods are critical links that connect the axle housing to the frame. They prevent the axle from rotating during acceleration and braking (axle wrap) and also maintain the axle's lateral and longitudinal alignment, which is essential for proper handling and driveline angles.

Question 96: When inspecting a trailer kingpin, which measurement determines whether it must be replaced?

The diameter of the kingpin shank measured at its wear zone (Correct answer)
The height of the kingpin above the trailer apron plate
The kingpin-to-apron plate bolt torque
The length of the kingpin below the apron plate

Correct answer: The diameter of the kingpin shank measured at its wear zone

Kingpin shank diameter is the critical wear measurement. Standards (such as CVSA) specify that a kingpin shank worn below a minimum diameter (typically 2 inches / 50.8 mm) must be replaced because excessive wear allows the fifth-wheel jaw to rock, creating coupling slop that can cause trailer separation. Height above and length below the plate are not wear measurements. Bolt torque ensures the kingpin is retained in the apron but does not measure kingpin condition.

Question 97: A vehicle's ABS wheel speed sensor produces an erratic signal. Which condition would MOST likely cause this?

Worn S-cam bushings
Excessive air gap between the sensor and tone ring (Correct answer)
Low reservoir pressure
Contaminated brake lining material

Correct answer: Excessive air gap between the sensor and tone ring

An excessive air gap between the sensor and exciter ring weakens the magnetic signal, causing the ECU to receive erratic or missing speed data.

Question 98: During a pre-trip inspection, a truck driver checks the fifth-wheel locking mechanism. Which condition would require the vehicle to be placed out of service before moving?

The locking jaw does not fully engage around the kingpin and the release handle moves freely (Correct answer)
The safety latch is resting against the release handle
The fifth wheel has a 5 mm side-to-side play when the trailer is coupled
Grease is visible on the fifth-wheel plate

Correct answer: The locking jaw does not fully engage around the kingpin and the release handle moves freely

If the locking jaw does not fully close around the kingpin and the release handle still moves freely, the trailer is not secured and could separate from the tractor — an immediately dangerous condition that requires the vehicle to be taken out of service. Grease on the plate is normal and required lubrication. A small amount of lateral play at the fifth wheel is acceptable and expected. The safety latch resting against the handle is its normal locked position.

Question 99: A technician is diagnosing an air suspension system on a coach where the rear of the vehicle is sitting lower than the specified ride height. The system builds air pressure normally and there are no audible leaks. What is the MOST likely cause?

A restricted air dryer.
A misadjusted or faulty height control valve. (Correct answer)
Worn shock absorbers.
A leaking air spring.

Correct answer: A misadjusted or faulty height control valve.

The height control valve is responsible for maintaining the correct ride height by adding or exhausting air from the air springs based on the vehicle's load. If the valve is misadjusted, its linkage is damaged, or the valve itself is faulty, it may not send enough air to the springs to achieve the correct height, even if there are no leaks in the system.

Question 100: What type of U-joint is used on heavy-duty truck driveshafts and requires periodic lubrication?

Rzeppa (ball-and-socket) joint
Tripod (triplex) joint
Giubo (doughnut) flex coupling
Cardan (cross-type) universal joint (Correct answer)

Correct answer: Cardan (cross-type) universal joint

The Cardan cross-type U-joint is standard on heavy truck driveshafts and has grease fittings on the bearing caps for periodic lubrication.

Question 101: A technician is sliding a trailer's tandem axle group rearward. What is the PRIMARY reason a driver would want the tandem positioned fully rearward?

To comply with maximum kingpin-to-rear-axle distance regulations
To maximize the load on the trailer's rear axles for better traction
To improve trailer stability at highway speeds
To shift weight rearward off the fifth wheel and reduce the drive axle load (Correct answer)

Correct answer: To shift weight rearward off the fifth wheel and reduce the drive axle load

Sliding the tandem rearward shifts load off the fifth wheel (and consequently off the tractor's drive axles) and places more weight on the trailer axles. Drivers do this to reduce drive-axle overloading. Sliding forward concentrates weight over the fifth wheel onto the drives. Stability is not improved by rearward tandem position (it can actually increase trailer sway). Kingpin-to-rear-axle distance regulations exist, but the primary operational reason for sliding rearward is axle-weight management.

Question 102: How is engine coolant freeze protection most accurately tested during preventive maintenance?

With a refractometer or hydrometer to measure specific gravity or freeze point (Correct answer)
By checking coolant color against a chart
By smelling the coolant for glycol odor
By observing the coolant level in the sight glass

Correct answer: With a refractometer or hydrometer to measure specific gravity or freeze point

A refractometer or hydrometer directly measures the antifreeze concentration, providing an accurate freeze point reading rather than an estimate.

Question 103: A diesel engine's DPF (diesel particulate filter) requires frequent active regeneration cycles. What underlying condition most likely causes this?

Cold ambient temperatures reducing exhaust temperature
High engine load operation that burns soot quickly
Using low-sulfur diesel fuel
Excessive oil consumption or fuel contamination causing excess soot production (Correct answer)

Correct answer: Excessive oil consumption or fuel contamination causing excess soot production

Excessive soot from burning engine oil or fuel dilution overloads the DPF faster than normal, triggering more frequent regeneration events.

Question 104: A diesel engine on a Class 8 truck exhibits intermittent low power complaints only under full load at highway speeds. Fuel pressure at the high-pressure pump inlet reads 45 psi at idle but drops to 18 psi during the load event. The OEM specification is a minimum 35 psi at all operating conditions. Which component failure is MOST likely causing this pressure drop?

A worn transfer pump (lift pump) unable to maintain adequate feed pressure under high-demand conditions (Correct answer)
A clogged high-pressure fuel filter restricting flow to the common rail
Air ingestion at the fuel tank pickup tube causing vapor lock under load
A faulty fuel pressure regulator holding pressure too low in the return circuit

Correct answer: A worn transfer pump (lift pump) unable to maintain adequate feed pressure under high-demand conditions

The transfer (lift) pump is responsible for supplying fuel to the high-pressure pump at adequate pressure under all operating conditions. At idle, demand is low and a worn transfer pump can still maintain pressure; however, under full load, the high-pressure pump requires maximum fuel flow, exposing the transfer pump's inability to keep up. A clogged high-pressure filter would cause a similar symptom but would typically also affect idle pressure. A pressure regulator fault would appear as a consistent, not load-dependent, issue. Air ingestion at the pickup would usually show as stalling or rough running rather than a clean pressure drop under load.

Question 105: During a dynamometer test on a heavy-duty truck engine, you observe that power output drops significantly above 1,800 RPM despite normal fuel pressure and injection timing. Exhaust backpressure measured at the turbocharger outlet is within spec. Which diagnostic step should be performed NEXT to isolate the root cause?

Replace the turbocharger compressor wheel and retest
Check the variable geometry turbocharger (VGT) actuator response across the full RPM range using a bidirectional scan tool (Correct answer)
Inspect the EGR cooler for internal leakage causing charge air dilution at higher loads
Perform a cylinder contribution test to identify cylinders with reduced power output at high RPM

Correct answer: Check the variable geometry turbocharger (VGT) actuator response across the full RPM range using a bidirectional scan tool

When power drops above a specific RPM threshold and exhaust backpressure at the turbo outlet is normal, the VGT actuator is the most likely culprit. A VGT that fails to open vanes sufficiently at higher RPMs restricts exhaust flow and limits boost. A bidirectional scan tool can command the VGT through its full range to verify actuator response versus commanded position — isolating mechanical sticking versus electronic failure before condemning any part. Cylinder contribution tests wouldn't explain an RPM-correlated pattern across all cylinders, and replacing the compressor wheel is premature without actuator verification.

Question 106: A truck's engine idles smoothly but stumbles when throttle is applied quickly. On a diesel, this most likely indicates:

Worn camshaft lobes
Faulty throttle position sensor
Low engine oil pressure
Turbocharger lag or restricted intake (Correct answer)

Correct answer: Turbocharger lag or restricted intake

Stumbling under rapid throttle application in a turbocharged diesel often results from turbo lag or a restricted air intake causing a momentary lean condition.

Question 107: Which regulation requires commercial motor vehicles to have their air brake systems inspected and certified annually?

49 CFR Part 393
49 CFR Part 396 (Correct answer)
49 CFR Part 383
49 CFR Part 390

Correct answer: 49 CFR Part 396

49 CFR Part 396 (Inspection, Repair, and Maintenance) requires annual vehicle inspections that include air brake system checks by a qualified inspector.

Question 108: Which hydraulic fluid property is MOST important when selecting fluid for a truck system that operates in both extreme cold and high-temperature conditions?

High flash point
Wide viscosity index (VI) (Correct answer)
High water content tolerance
Low specific gravity

Correct answer: Wide viscosity index (VI)

Viscosity Index (VI) describes how much a fluid's viscosity changes with temperature. A high VI means the fluid stays within an acceptable viscosity range from cold start through full operating temperature, protecting pumps and seals in both extremes. Flash point relates to fire safety, not temperature range performance; water tolerance and specific gravity are not the primary selection criteria for wide-temperature operation.

Question 109: During a preventive maintenance inspection on a heavy-duty diesel truck, you discover that the coolant recovery tank is consistently losing fluid between service intervals, but there are no visible external leaks and the engine is not overheating. Which of the following is the MOST likely cause requiring further diagnosis?

Electrolytic corrosion from stray electrical current causing slow dezincification of brass cooling components
A faulty radiator pressure cap that is venting coolant vapor past its set pressure prematurely
A minor internal head gasket leak combusting coolant without producing visible white exhaust smoke at operating temperature (Correct answer)
Air ingestion into the cooling system through a cracked surge tank causing coolant displacement

Correct answer: A minor internal head gasket leak combusting coolant without producing visible white exhaust smoke at operating temperature

A minor internal head gasket breach can allow combustion gases to enter the cooling system without producing noticeable white exhaust smoke, especially if the leak is small enough that coolant burns off gradually. This causes slow coolant loss from the recovery tank without visible external leaks. The combustion gases also raise system pressure intermittently, which can push coolant into the overflow. A faulty pressure cap would typically cause overheating, not just tank depletion. Air ingestion would produce gurgling and temperature fluctuation. Electrolytic corrosion causes component degradation, not net fluid loss.

Question 110: A truck's diesel particulate filter (DPF) regeneration is inhibited even though exhaust back-pressure is above threshold and all regeneration enable conditions appear met. The technician notices that the diesel exhaust fluid (DEF) quality sensor is reporting a fault code for low DEF concentration. How does this sensor fault DIRECTLY cause regeneration inhibit?

The aftertreatment control module inhibits active regeneration when SCR system faults are present to prevent injecting unburned hydrocarbons into a compromised SCR catalyst (Correct answer)
The DPF differential pressure sensor shares a CAN node with the DEF quality sensor, and a fault on that node disables all aftertreatment sensor inputs
Low DEF concentration causes the NOx sensors downstream of the SCR to read high, and the ECM interprets high NOx as a sign that exhaust temperatures are too low for safe regeneration
The DEF doser relies on the same high-pressure fuel circuit as the in-cylinder post-injection used for active regeneration, so a DEF fault locks out fuel delivery

Correct answer: The aftertreatment control module inhibits active regeneration when SCR system faults are present to prevent injecting unburned hydrocarbons into a compromised SCR catalyst

Modern aftertreatment systems treat the DPF and SCR as an integrated system. If the SCR is compromised (detected via DEF quality, NOx sensor, or doser faults), the ACM will inhibit active DPF regeneration because the hydrocarbon dosing required for regeneration would pass through or over a non-functional SCR catalyst, releasing uncontrolled NOx and HC emissions. This is an intentional OBD/emissions protection strategy. The other options misattribute the control logic or describe non-existent circuit relationships.

Question 111: A technician notices the crankcase pressure is excessive and oil is pushed out through seals. What test should be performed first?

Turbocharger boost pressure test
Fuel pressure test
Coolant pressure test
Cylinder leakdown test (Correct answer)

Correct answer: Cylinder leakdown test

A cylinder leakdown test identifies which cylinders are passing combustion gases into the crankcase, causing excessive blow-by pressure.

Question 112: A motorcoach with air suspension repeatedly triggers the low-ride-height warning on one rear corner. The air spring, height control valve, and supply air check out fine. What should be inspected next?

Brake chamber push rod travel
Suspension torque rods for looseness
Air lines and fittings for slow leaks between the height control valve and the air spring (Correct answer)
Ride height sensor calibration

Correct answer: Air lines and fittings for slow leaks between the height control valve and the air spring

Slow leaks in the air lines between the height control valve and spring allow the spring to bleed down when stationary, triggering the low-height warning.

Question 113: A straight truck equipped with a single circuit S-cam foundation brake shows excessive brake fade during repeated high-speed stops from 60 mph. Lining thickness, drum diameter, and pushrod stroke are all within specification. The driver reports the pedal 'goes lower' on successive stops. Reservoir pressure remains stable at 110 psi. Which diagnosis BEST explains all symptoms together?

Automatic slack adjuster over-adjusting, increasing applied torque and causing thermal runaway in the lining compound
Brake chamber diaphragm thermally deforming under repeated application, reducing effective area and net clamping force
S-cam roller follower wear causing cam-to-roller separation during application, reducing mechanical advantage progressively as components heat (Correct answer)
Brake valve graduating spring fatigue causing proportionally lower delivery pressure on successive applications

Correct answer: S-cam roller follower wear causing cam-to-roller separation during application, reducing mechanical advantage progressively as components heat

As S-cam roller followers wear, the roller no longer maintains consistent contact geometry with the cam profile. When components heat from repeated stops, thermal expansion of the cam, rollers, and shoes changes clearances. Worn rollers allow intermittent cam-to-roller separation, meaning the cam must rotate further to generate the same shoe movement — effectively reducing mechanical advantage. This explains the progressively lower pedal feel (more chamber stroke needed), brake fade despite stable air pressure, and correct stroke measurements taken cold. Diaphragm deformation is rarely thermal; slack adjuster over-adjustment would increase, not decrease, clamping force.

Question 114: A Class 8 truck with a recirculating ball steering gear exhibits excessive wander at highway speeds. After confirming proper tire inflation, wheel alignment, and front axle preload, the technician measures 6° of total steering wheel freeplay. The steering gear was recently rebuilt. Which condition is MOST likely causing this symptom?

Worn sector shaft-to-piston mesh point adjusted too loose during rebuild (Correct answer)
Excessive positive caster causing directional instability
Insufficient hydraulic pump pressure at high engine RPM
Pittman arm splined connection slipping under load

Correct answer: Worn sector shaft-to-piston mesh point adjusted too loose during rebuild

Excessive freeplay in a recently rebuilt recirculating ball gear most often points to improper sector shaft-to-piston (over-center) mesh adjustment. The mesh point is set tightest at the straight-ahead position; if adjusted with too much lash, it creates the measured freeplay and highway wander. Caster affects returnability more than wander, Pittman arm slip would cause sudden loss of steering control rather than gradual wander, and pump pressure drop at high RPM is not a common presentation.

Question 115: Which component prevents moisture and contaminants from entering the air brake system from the compressor?

Wet tank drain
Air dryer (Correct answer)
Unloader valve
Pressure protection valve

Correct answer: Air dryer

The air dryer removes moisture and oil vapor from compressor discharge air before it reaches the reservoirs, preventing corrosion and freezing.

Question 116: Which credential allows a licensed 310T technician to legally sign off on a heavy vehicle inspection certificate in Ontario?

Red Seal plus DOT card
Ministry of Transport endorsement sticker
Motor Vehicle Inspection Station (MVIS) authorization (Correct answer)
Certificate of Qualification only

Correct answer: Motor Vehicle Inspection Station (MVIS) authorization

In Ontario, a technician must hold or work under a Motor Vehicle Inspection Station (MVIS) authorization to sign off on official vehicle inspection certificates.

Question 117: During a forced regeneration of a Diesel Particulate Filter (DPF), what is the primary method used by the engine control module (ECM) to increase the exhaust gas temperature to the required level for soot oxidation?

Increasing the engine idle speed to maximum RPM
Closing the vanes on the variable geometry turbocharger (VGT)
Activating the engine's compression brake
Injecting a small amount of fuel into the exhaust stream during the exhaust stroke (Correct answer)

Correct answer: Injecting a small amount of fuel into the exhaust stream during the exhaust stroke

Active and forced DPF regeneration require exhaust temperatures of around 600°C (1112°F) to burn off trapped soot. The most common method to achieve this is by post-combustion injection, where a small amount of diesel fuel is injected late in the exhaust stroke. This unburnt fuel travels to the Diesel Oxidation Catalyst (DOC) upstream of the DPF, where it oxidizes and generates significant heat, raising the exhaust temperature for DPF regeneration.

Question 118: In S-cam foundation brakes, what converts the rotational force of the cam into outward shoe movement?

Brake spider
Return spring
Anchor pin
Roller followers on the brake shoes (Correct answer)

Correct answer: Roller followers on the brake shoes

Rollers at the toe of each brake shoe ride the lobes of the S-cam; as the cam rotates, the rollers are pushed apart, forcing the shoes outward against the drum.

Question 119: When rebuilding a recirculating ball steering gear on a coach, the technician sets the worm bearing preload to spec using a torque wrench at the input shaft. After reassembly on the vehicle, the steering feels excessively heavy on-center but loosens off-center. What adjustment error was most likely made?

The hydraulic relief valve pressure was set too low
The sector shaft over-center preload was set without first properly centering the gear, creating excessive mesh load at center (Correct answer)
The pitman arm was installed one spline off, shifting the center point
The worm bearing preload was set too high

Correct answer: The sector shaft over-center preload was set without first properly centering the gear, creating excessive mesh load at center

In a recirculating ball steering gear, the sector shaft over-center adjustment must be made with the gear precisely at the centered (straight-ahead) position. If the gear is not correctly centered before the over-center adjuster is tightened, the point of maximum mesh (highest preload) ends up offset from true center. The result is heavy, binding steering near the actual center position while feeling correct or loose off-center — which is the reverse of the intended design where minimal preload exists off-center.

Question 120: What causes diesel engine 'cavitation erosion' damage to cylinder liners?

High fuel sulfur content attacking the liner surface
Abrasive particles in the engine oil
Coolant pressure fluctuations causing vapor bubble collapse on the liner exterior (Correct answer)
Improper piston ring gap causing liner scuffing

Correct answer: Coolant pressure fluctuations causing vapor bubble collapse on the liner exterior

Cavitation erosion occurs when coolant pressure waves cause vapor bubbles to form and implode against the wet cylinder liner's outer surface.

Question 121: After rebuilding the foot valve (treadle valve) on a truck, a technician notices that at partial brake applications, there is a notable delay before the brakes release after the pedal is lifted, but full applications release promptly. What assembly error MOST likely caused this?

The exhaust valve seat was lapped excessively, reducing the exhaust orifice area and slowing release at low differential pressures
The exhaust cover was installed with the exhaust port partially blocked by a misaligned gasket
The treadle valve piston was installed without lubricant, causing it to stick under low-pressure conditions
The primary and secondary graduating springs were installed in reversed order, altering the graduating force curve (Correct answer)

Correct answer: The primary and secondary graduating springs were installed in reversed order, altering the graduating force curve

Reversing the primary and secondary graduating springs changes the force-versus-travel relationship of the valve. At low pedal force (partial application), the altered spring stack creates a condition where the graduating piston does not return to the exhaust position promptly — because the spring load balance that normally overcomes delivery pressure at low application levels is disrupted. At full application, line pressure itself overcomes the mechanical resistance and releases normally. An exhaust orifice restriction or blocked port would uniformly slow all releases, not specifically partial ones.

Question 122: A truck's Tire Pressure Monitoring System (TPMS) warning light illuminates at highway speed but goes out after 15 minutes of driving. What is the MOST likely explanation?

A slow leak in one tire that sealed itself due to centrifugal force at highway speed
Normal tire pressure increase from heat build-up bringing pressure back above the warning threshold (Correct answer)
The TPMS receiver antenna is loose and losing signal intermittently
A faulty TPMS sensor that needs replacement

Correct answer: Normal tire pressure increase from heat build-up bringing pressure back above the warning threshold

Cold-inflation pressure can be several psi below the warm operating pressure because air expands as the tire heats up from friction and flexing. If a tire starts slightly underinflated (close to the TPMS warning threshold), the light may trigger until the tire warms up and pressure rises above the threshold. This is why TPMS specs are based on cold inflation pressure — the vehicle should be parked and tires checked cold to confirm actual inflation status.

Question 123: The SAE J1939 standard is a high-level protocol used for communication and diagnostics between ECUs on a commercial vehicle. On which underlying network technology is J1939 built?

Ethernet
FlexRay
LIN Bus
Controller Area Network (CAN) (Correct answer)

Correct answer: Controller Area Network (CAN)

SAE J1939 defines the communication language and data structure (the software protocol) that runs on top of the physical Controller Area Network (CAN) bus (the hardware). CAN provides the physical and data-link layers for the J1939 protocol to operate.

Question 124: A spring brake actuator (piggyback chamber) is being replaced. After installation and system pressurization, the parking brake releases correctly, but during a full-pressure service brake application the pushrod travel is 25% less than the adjacent chamber on the same axle. The new chamber's clamp band and mounting are correct. What should the technician check FIRST?

The hold-off pressure setting of the spring brake section
The slack adjuster arm length on that wheel position
The service brake side diaphragm for a manufacturing defect
The size rating of the replacement chamber versus the original specification (Correct answer)

Correct answer: The size rating of the replacement chamber versus the original specification

Piggyback spring brake chambers are available in multiple size combinations (e.g., 30/30, 24/24, 30/24). If the wrong service-side chamber size was installed, its diaphragm area is smaller, producing less pushrod force and travel for a given air pressure. This is a common error during replacement. A manufacturing defect in the diaphragm would more likely cause complete failure or severe air leakage. Hold-off pressure affects only the spring section release, not service brake stroke. Slack adjuster arm length is a separate assembly and would not change the chamber's pushrod travel.

Question 125: A technician is performing fuel injector balance testing on a HEUI (Hydraulically-actuated Electronically-controlled Unit Injector) system. One injector shows a significantly lower contribution than the others, but the injector passes a leak-down test. What should the technician investigate NEXT?

The injection actuation pressure control valve for system-wide pressure faults
The injector solenoid coil resistance and the Injector Driver Module (IDM) output for that cylinder (Correct answer)
The low-pressure fuel supply to the high-pressure oil pump
The air-fuel ratio sensor downstream of the affected cylinder's exhaust port

Correct answer: The injector solenoid coil resistance and the Injector Driver Module (IDM) output for that cylinder

In a HEUI system, the injector is actuated by high-pressure engine oil controlled by a solenoid. If the injector passes a leak-down test (meaning the hydraulic and fuel check components are mechanically sound), the fault lies in the electrical actuation circuit — specifically the solenoid coil resistance or the Injector Driver Module (IDM) output signal for that cylinder. A weak or missing IDM pulse would prevent full actuation, causing low fuel delivery without mechanical failure. The actuation pressure valve affects all cylinders equally, and a diesel does not use per-cylinder exhaust sensors in this context.

Question 126: A technician is bleeding a hydraulic braking system on a coach. What is the correct procedure to ensure all air is removed?

Bleed only the wheel cylinder furthest from the master cylinder first (Correct answer)
Start at the caliper closest to the master cylinder and work outward
Begin at the highest point in the system and work downward, ending at the master cylinder
Crack all bleed screws simultaneously and apply steady pressure until fluid runs clear

Correct answer: Bleed only the wheel cylinder furthest from the master cylinder first

Air rises, so the caliper farthest from the master cylinder — and typically the one with the longest fluid path — is bled first to push trapped air completely through the system. Bleeding closest to the master cylinder first risks trapping air in the long downstream lines. Opening all screws simultaneously causes uncontrolled pressure loss. Bleeding from the highest point is a principle used in cooling systems, not hydraulic brake circuits.

Question 127: What is the maximum allowable brake lining thickness before replacement is required per FMCSA brake regulations?

Replacement is required at 25% of original thickness
4 mm everywhere
1/16 inch on steering axle, 1/8 inch on other axles
1/4 inch on steering axle, 1/8 inch elsewhere (Correct answer)

Correct answer: 1/4 inch on steering axle, 1/8 inch elsewhere

FMCSA (49 CFR 393.47) specifies minimum lining thickness of 1/4 inch on steering axles and 1/8 inch on all other axles before the vehicle is placed out of service.

Question 128: While performing a voltage drop test across a starter motor circuit on a diesel truck, the technician measures 0.9V drop across the positive battery cable, 0.1V across the starter solenoid main contacts, and 0.2V across the negative cable. Total circuit drop is 1.2V. The starter cranks slowly. Which corrective action is MOST appropriate?

Replace the starter motor, as the combined 1.2V drop indicates it is drawing excessive current
Load-test the battery; a weak battery causes high voltage drop readings throughout the circuit
Replace or recondition the positive battery cable, as its 0.9V drop represents the dominant resistance fault (Correct answer)
Replace the starter solenoid, as contact resistance should be below 0.05V under load

Correct answer: Replace or recondition the positive battery cable, as its 0.9V drop represents the dominant resistance fault

Voltage drop testing distributes the responsibility across each segment of the circuit. The industry standard for a starter circuit is a maximum total drop of about 0.5V, with individual cable drops not exceeding 0.2V. The positive cable at 0.9V is carrying the vast majority of the resistance fault — nearly 75% of the total drop. This indicates corrosion, internal cable degradation, or a loose terminal in that cable. The solenoid contact drop of 0.1V and negative cable drop of 0.2V are borderline but secondary. Addressing the dominant fault first is correct diagnostic procedure.

Question 129: A driver reports that the trailer ABS warning lamp on the dashboard is continuously illuminated, but the tractor ABS lamp functions normally (cycles on and off at startup). What is the MOST likely location of the fault?

The brake treadle valve position sensor.
A faulty wheel speed sensor or wiring on a trailer axle. (Correct answer)
The main ABS electronic control unit (ECU) on the tractor.
The gladhand seals between the tractor and trailer.

Correct answer: A faulty wheel speed sensor or wiring on a trailer axle.

The tractor and trailer have separate ABS systems that communicate. If the tractor's ABS light is off but the trailer's is on, the fault lies within the trailer's ABS components. A failed wheel speed sensor or damaged wiring to the sensor is the most common cause of a persistent trailer ABS fault.

Question 130: A driver reports that their truck, equipped with an Automated Manual Transmission (AMT), intermittently fails to engage a starting gear from neutral. Diagnostic trouble codes point to a fault in the gear selection system. Which of the following components is the MOST likely cause?

A worn-out main shaft synchronizer
A clogged transmission fluid filter
A faulty electronic shift actuator (Correct answer)
A low-voltage condition at the TCM

Correct answer: A faulty electronic shift actuator

AMTs use electronic actuators (motors or solenoids) to physically move the shift forks and engage gears based on commands from the Transmission Control Module (TCM). A failure or intermittent fault in one of these actuators would directly prevent the transmission from selecting and engaging a gear. [33] While other issues could cause shifting problems, a gear selection fault code points most directly to the component that performs the physical selection.

Question 131: What type of exam format is commonly used in the written component of the certification test?

Oral interviews
Practical demonstrations
Multiple-choice questions (Correct answer)
Essay-style responses

Correct answer: Multiple-choice questions

The written component of the Truck and Coach Technician certification test commonly utilizes multiple-choice questions to efficiently assess a broad range of theoretical knowledge. This format allows for standardized scoring and covers various essential topics, from engine systems and electrical diagnostics to safety procedures and regulatory compliance.

Question 132: Landing gear on a semi-trailer is designed to support the trailer when uncoupled. What type of lubrication is typically specified for landing gear gearbox maintenance?

Automatic transmission fluid (ATF)
Gear oil such as SAE 90 or equivalent (Correct answer)
Engine oil SAE 15W-40
Chassis grease (NLGI #2)

Correct answer: Gear oil such as SAE 90 or equivalent

Landing gear gearboxes are small enclosed gear sets that require gear oil (typically SAE 90 or a manufacturer-specified GL-4/GL-5 equivalent) to lubricate the worm gear and bevel gears under high load. Engine oil is not formulated for gear mesh pressures. NLGI #2 grease is used for external fittings such as the leg tube, not the enclosed gearbox. ATF is designed for automatic transmissions and is not specified for landing gear gearboxes.

Question 133: On a coach with a multiplexed body control system, a technician wants to verify that a door switch input is being received by the BCM. The BEST method is:

Backprobe the switch with a test light
Use a scan tool to monitor the BCM's live input data stream (Correct answer)
Replace the BCM and retest
Measure voltage at the BCM harness connector with a DVOM

Correct answer: Use a scan tool to monitor the BCM's live input data stream

A scan tool's live data stream shows exactly what the BCM is seeing from its inputs, confirming whether the signal is reaching the module without intrusive probing.

Question 134: A coach bus with a fully automatic transmission exhibits hunting between 4th and 5th gear only when the A/C compressor cycles on under a 60–70% throttle load. All transmission shift solenoids test within spec. What is the MOST LIKELY underlying cause?

Low transmission fluid causing aeration and inconsistent clutch pack apply pressure
The A/C compressor load increase is momentarily reducing available engine torque below the transmission's upshift threshold, causing oscillation (Correct answer)
A faulty throttle position sensor sending intermittent high-load signals to the TCM
Worn torque converter clutch causing slippage during the shift event

Correct answer: The A/C compressor load increase is momentarily reducing available engine torque below the transmission's upshift threshold, causing oscillation

At 60–70% throttle, the engine is near the boundary condition that triggers 4-to-5 upshift. When the A/C compressor engages, it parasitically draws power, momentarily reducing net engine torque. The TCM detects insufficient torque for 5th gear efficiency and commands a downshift; as the engine re-stabilizes, it upshifts again — creating the hunting pattern. This is a well-known edge case in coach diagnostics. The fix typically involves reprogramming the TCM to account for A/C compressor load or adjusting the shift inhibit logic. The other options would not create a pattern so tightly correlated to A/C cycling.

Question 135: A relay valve is delivering pressure to the rear brake chambers that is 20 psi higher than the signal pressure. This indicates:

A faulty governor allowing excessive pressure
Normal proportioning for loaded conditions
A stuck open delivery valve causing constant full pressure delivery (Correct answer)
A correct operation — relay valves amplify signal pressure

Correct answer: A stuck open delivery valve causing constant full pressure delivery

A relay valve should deliver pressure equal to its signal input; delivery pressure significantly exceeding signal pressure indicates a stuck delivery valve allowing uncontrolled reservoir air flow.

Question 136: When testing a tractor protection valve, a technician disconnects the gladhands and observes that the tractor supply line (emergency line) drops from 120 psi to 0 psi within 8 seconds with the engine running and governor maintaining system pressure. What condition does this MOST accurately indicate?

A leaking trailer supply reservoir check valve is drawing air from the tractor circuit
The tractor protection valve is operating correctly — emergency line dumps are normal when gladhands are disconnected
The tractor protection valve has a damaged seat, preventing it from closing when line pressure drops below the trip threshold (Correct answer)
The tractor protection valve is stuck open, allowing continuous compressor output to vent through the disconnected line

Correct answer: The tractor protection valve has a damaged seat, preventing it from closing when line pressure drops below the trip threshold

The tractor protection valve should CLOSE the emergency supply line when line pressure drops below approximately 20–45 psi (the trip threshold), isolating the tractor system from an open gladhand. A rapid drop to 0 psi with a running compressor means the valve is not closing — a damaged seat or broken internal spring prevents sealing, allowing the compressor to continuously vent through the open line. If it were functioning correctly, the valve would close and the tractor tanks would hold pressure. A stuck-open valve description is close, but the root cause is seat damage preventing closure at the trip threshold, not a valve mechanically jammed open at all times.

Question 137: A hydraulic lift gate on a truck drops slowly under load even though the pump motor runs continuously. What is the MOST likely cause?

Low hydraulic fluid level
A worn or bypassing hydraulic pump (Correct answer)
A blocked filter restricting return flow
An incorrectly adjusted relief valve set too high

Correct answer: A worn or bypassing hydraulic pump

When the pump runs but the cylinder cannot hold load under continuous demand, internal pump wear causes fluid to bypass internally, reducing effective flow and pressure. Low fluid would also cause slow operation but typically stalls intermittently; a blocked return filter increases back-pressure rather than causing bypass; and a relief valve set too high would allow excessive pressure, not cause slow descent.

310T Truck and Coach Technician Exam

The 310T Truck and Coach Technician certification exam (Red Seal / Skilled Trades Ontario) validates competency in diagnosing, repairing, and servicing commercial trucks, buses, and coaches.

135

Questions

240 min

Time Limit

70%

To Pass

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