Mixed Deck — All 310S Topics Flashcards

What does a waveform with missing humps on an alternator AC ripple test indicate?

Answer: One or more failed rectifier diodes

A normal three-phase alternator produces a smooth ripple pattern. Missing humps indicate that one or more rectifier diodes have failed, preventing that phase's output from contributing to the DC supply.

What is the purpose of the emergency brake assist (BA) system?

Answer: To detect a panic braking situation and automatically apply maximum braking force faster than the driver can

Brake assist monitors the speed and force of brake pedal application. If it detects a panic stop (fast pedal application), it immediately applies full braking force, reducing stopping distance for drivers who may not press hard enough.

When testing a Hall-effect sensor, what type of signal output should a technician expect?

Answer: A digital square wave signal switching between high and low voltage

Hall-effect sensors produce a clean digital square wave signal that switches between a reference voltage (high) and ground (low) as a trigger wheel or shutter blade passes through the sensor's magnetic field.

What causes a vibration felt throughout the vehicle during acceleration from a stop?

Answer: Worn universal joints (U-joints) on the driveshaft

Worn U-joints develop play that causes the driveshaft to vibrate during acceleration. The vibration is typically felt at low speeds and during acceleration when the most torque is transmitted through the drivetrain.

What is the purpose of the proportioning valve in a brake system?

Answer: To reduce hydraulic pressure to the rear brakes to prevent premature rear wheel lockup during braking

During braking, weight transfers to the front wheels, reducing rear wheel traction. The proportioning valve limits pressure to the rear brakes, preventing them from locking up before the front brakes.

A front-wheel-drive vehicle exhibits a humming noise that changes with vehicle speed but not engine RPM. The noise changes tone when swerving left or right. What is the most likely cause?

Answer: A worn wheel bearing

A speed-dependent humming that changes with lateral load (swerving) is characteristic of a worn wheel bearing. Swerving loads or unloads the bearing, changing the noise. The sound does not change with engine RPM since it is driven by wheel speed.

What is the purpose of the immobilizer system in a modern vehicle?

Answer: To disable the fuel and/or ignition system unless the correct transponder key is detected

The immobilizer system communicates with a transponder chip in the key. If the correct code is not received, the system disables fuel injection and/or ignition, preventing the engine from starting even if the key turns.

A compression test on a four-cylinder engine shows cylinders 1, 2, and 4 at 150 psi, but cylinder 3 reads 90 psi. What should the technician do next?

Answer: Perform a wet compression test on cylinder 3

A wet compression test adds oil to the cylinder. If compression rises significantly, the rings are worn. If it stays low, the issue is likely valves or a head gasket leak.

What is the function of the brake caliper?

Answer: To house the brake piston(s) and clamp the brake pads against the rotor when hydraulic pressure is applied

The brake caliper straddles the brake rotor and contains one or more hydraulic pistons. When pressure is applied, the piston(s) push the brake pads against the rotor, creating friction to slow the wheel.

A technician observes a downstream oxygen sensor signal that is flat at approximately 0.45 volts. What does this indicate?

Answer: The catalytic converter is functioning efficiently

A properly functioning catalytic converter stores and releases oxygen, smoothing out the exhaust gas composition. The downstream O2 sensor should show a relatively steady voltage near 0.45V, indicating efficient conversion.

What is the correct procedure for performing a four-wheel alignment?

Answer: Adjust the rear alignment first, then align the front wheels to the rear thrust line

The rear wheels are adjusted first to establish the thrust angle. The front wheels are then aligned to the thrust angle so the vehicle tracks straight. This ensures the steering wheel is centred and the vehicle doesn't dog-track.

A vehicle has a P0420 code (catalyst system efficiency below threshold, bank 1). What is the most common cause?

Answer: A deteriorated catalytic converter that can no longer efficiently convert emissions

P0420 indicates the downstream O2 sensor signal closely mirrors the upstream sensor, meaning the catalytic converter is no longer storing and releasing oxygen effectively. The converter's catalyst material has deteriorated.

A vehicle fails an emissions test for high NOx levels. What is the most likely cause?

Answer: A malfunctioning EGR system or excessive combustion temperatures

High NOx emissions are caused by excessive combustion temperatures. A non-functioning EGR system fails to lower peak temperatures, and lean conditions or cooling system problems can also contribute to high NOx.

What is the purpose of the transmission valve body?

Answer: To direct hydraulic fluid flow through a series of valves and passages to control clutch application, shift timing, and line pressure

The valve body is the hydraulic control centre of an automatic transmission. It contains numerous spool valves, check balls, and fluid passages that direct pressurized ATF to apply and release clutch packs and bands in the correct sequence.

What is the correct procedure for measuring cylinder bore out-of-round?

Answer: Use a telescoping gauge or bore gauge at thrust and non-thrust sides at the same height

Out-of-round is determined by measuring the bore diameter at the thrust side (perpendicular to the crankshaft) and non-thrust side (parallel to the crankshaft) at the same height, then comparing the readings.

What does the ABS warning light illuminating during normal driving indicate?

Answer: A fault has been detected in the ABS system and antilock function is disabled

The ABS warning light indicates the ABS control module has detected a fault and has disabled antilock braking. The base brake system still functions normally, but the wheels can lock during hard braking.

What is indicated by a continuously fluctuating vacuum gauge reading at idle?

Answer: A worn camshaft lobe or weak valve spring

A fluctuating vacuum reading at idle indicates inconsistent cylinder sealing, commonly caused by a worn camshaft lobe that fails to fully open a valve or a weak valve spring that allows valve float.

What is the function of the accumulator in an automatic transmission hydraulic circuit?

Answer: To cushion the application of a clutch pack by temporarily absorbing hydraulic pressure, providing smooth shift engagement

Accumulators use a spring-loaded piston in a bore to temporarily absorb some of the apply pressure during a shift, cushioning the engagement of the clutch pack for a smooth, controlled shift feel.

How does the ECM detect a misfire?

Answer: By monitoring crankshaft speed variations through the crankshaft position sensor

The ECM monitors crankshaft rotational speed via the CKP sensor. When a cylinder misfires, it fails to contribute its power pulse, causing a measurable deceleration in crankshaft speed that the ECM identifies as a misfire.

A four-gas exhaust analyzer shows high CO and high HC readings. What condition does this indicate?

Answer: A rich fuel mixture with incomplete combustion

High CO indicates a rich mixture (excess fuel not fully oxidized). High HC indicates unburned fuel passing through. Together, they point to a rich condition with incomplete combustion from excess fuel.