310T Evaluation and Testing Process 2 — Questions and Answers
Question 1: During a road test evaluation of a Class 8 truck, the technician notices the vehicle pulls to the right when braking. What is the MOST likely cause?
- Unequal tire inflation pressure front-to-rear
- A seized or dragging brake on the left front axle (Correct answer)
- Excessive positive caster on the right side
- Worn rear axle U-joints
Correct answer: A seized or dragging brake on the left front axle
A dragging or seized brake on the opposite side of the pull causes unequal braking force, pulling the vehicle toward the stuck brake.
Question 2: A coach technician is performing a pre-inspection before road testing a bus with a reported rough idle. What should be done FIRST?
- Connect a scan tool to retrieve active fault codes (Correct answer)
- Perform a visual inspection under the hood with engine off
- Start the engine and listen for abnormal noises
- Check transmission fluid level and condition
Correct answer: Connect a scan tool to retrieve active fault codes
Retrieving active fault codes first gives direction and prevents overlooking stored diagnostic information before starting other tests.
Question 3: When using an oscilloscope to evaluate a crankshaft position sensor signal on a diesel engine, a good waveform should show:
- A consistent square wave with no amplitude variation
- A sine or digital pattern with a missing tooth gap at TDC reference (Correct answer)
- A flat line at 5V between pulses
- Random frequency variation proportional to throttle position
Correct answer: A sine or digital pattern with a missing tooth gap at TDC reference
The crankshaft position sensor produces a pattern with a deliberate missing tooth gap that the ECM uses as a TDC reference point.
Question 4: A technician is evaluating a hydraulic power steering system on a truck. Steering effort is high at low speeds but normal at highway speeds. The MOST likely cause is:
- Worn tie rod ends allowing excessive play
- A clogged power steering filter or low fluid level (Correct answer)
- A faulty speed-sensitive valve stuck in the high-assist position
- Excessive positive toe misalignment
Correct answer: A clogged power steering filter or low fluid level
A clogged filter or low fluid restricts flow and pressure, reducing assist most noticeably at low speeds when demand is highest.
Question 5: During evaluation of a truck's air brake system, the governor cut-in pressure is found to be 95 psi and cut-out is 130 psi. This indicates:
- Normal operation within FMCSA specifications
- A governor with an excessively wide pressure band that should be replaced (Correct answer)
- Low cut-in pressure that may cause brake fade on grades
- Normal cut-out but cut-in is too high for safe operation
Correct answer: A governor with an excessively wide pressure band that should be replaced
FMCSA regulations require the pressure differential between cut-in and cut-out to not exceed 25 psi; a 35 psi spread indicates a faulty governor.
Question 6: When evaluating exhaust back pressure on a diesel engine, a reading of 3.5 inches Hg at rated RPM indicates:
- Normal back pressure within acceptable limits (Correct answer)
- Slightly elevated pressure worth monitoring but not yet critical
- Excessive back pressure requiring immediate DPF or exhaust inspection
- A malfunctioning back pressure sensor that reads too high
Correct answer: Normal back pressure within acceptable limits
Most diesel engine manufacturers specify a maximum allowable exhaust back pressure of 3.5 to 4.0 inches Hg, so 3.5 is within normal range.
Question 7: A technician is evaluating the coolant system on a coach and finds the pressure cap releases at 12 psi on a system rated for 15 psi. What should be done?
- Continue testing; a 3 psi variance is acceptable
- Replace the pressure cap as it is releasing below rated pressure (Correct answer)
- Flush the cooling system and refill with fresh coolant
- Inspect the radiator for internal blockage
Correct answer: Replace the pressure cap as it is releasing below rated pressure
A pressure cap releasing below its rated pressure reduces the coolant boiling point and can cause overheating; the cap must be replaced.
310T Evaluation and Testing Process 2
During a road test evaluation of a Class 8 truck, the technician notices the vehicle pulls to the right when braking.
What is the MOST likely cause?