310T Evaluation and Testing Process 3 — Questions and Answers
Question 1: When testing a truck's automatic transmission for slippage, the BEST method is to perform a:
- Fluid level check at operating temperature
- Stall speed test comparing RPM against the manufacturer's specification (Correct answer)
- Road test in overdrive on a flat highway
- Drain and inspect the transmission pan for metal debris only
Correct answer: Stall speed test comparing RPM against the manufacturer's specification
A stall speed test measures engine RPM when the torque converter is stalled against the transmission load, revealing clutch pack or torque converter slippage.
Question 2: During functional testing of a truck's ABS system, the amber ABS warning lamp remains illuminated after the vehicle exceeds 6 mph. This indicates:
- Normal lamp behavior during initial self-test
- A fault detected by the ABS ECU requiring further diagnosis (Correct answer)
- A bulb stuck in the on position due to a short to ground
- Low air pressure preventing ABS activation
Correct answer: A fault detected by the ABS ECU requiring further diagnosis
The ABS lamp should extinguish above approximately 4–6 mph once the system self-test passes; continued illumination signals an active fault code.
Question 3: A technician is evaluating cylinder contribution on a diesel engine using a cylinder cut-out test. If cutting out a cylinder causes no RPM drop, this suggests:
- That cylinder has excessive compression
- That cylinder is not contributing power and may have a fuel, injection, or mechanical issue (Correct answer)
- The engine is running too rich overall
- Normal operation for a heavily loaded engine
Correct answer: That cylinder is not contributing power and may have a fuel, injection, or mechanical issue
A cylinder that is already not firing or contributing negligible power shows no RPM change when cut out, confirming it is a problem cylinder.
Question 4: When performing a voltage drop test on a starter motor circuit on a heavy-duty truck, the maximum acceptable voltage drop across the positive battery cable is:
- 0.5 volts (Correct answer)
- 1.0 volt
- 2.0 volts
- 3.0 volts
Correct answer: 0.5 volts
Industry standard allows no more than 0.5 volts drop across each heavy cable in the starter circuit to ensure adequate cranking voltage.
Question 5: A coach's air conditioning system is evaluated and the high-side pressure is 375 psi with an ambient temperature of 90°F. This reading indicates:
- Normal high-side pressure for that ambient temperature
- Overcharge of refrigerant or a condenser airflow restriction (Correct answer)
- Low refrigerant charge causing high compression ratio
- A faulty high-side pressure transducer
Correct answer: Overcharge of refrigerant or a condenser airflow restriction
High-side pressures significantly above the normal range for ambient temperature (typically around 200–250 psi at 90°F for R-134a) indicate overcharge or blocked condenser airflow.
Question 6: When evaluating a Class 8 truck's fifth wheel coupling, a technician should test jaw engagement by:
- Visually inspecting from the side of the trailer only
- Attempting to separate the tractor from the trailer by pulling forward with brakes set (Correct answer)
- Measuring jaw gap with a feeler gauge only
- Checking kingpin height with a tape measure
Correct answer: Attempting to separate the tractor from the trailer by pulling forward with brakes set
The tug test—pulling the tractor forward against set trailer brakes—is the standard functional check to confirm the jaws are fully locked around the kingpin.
Question 7: During evaluation of a hydraulic retarder on a coach, the retarder provides no braking effort when engaged. The FIRST test should be to:
- Rebuild the retarder control valve assembly
- Check hydraulic fluid level and retarder control pressure (Correct answer)
- Inspect the driveline for broken U-joints
- Replace the retarder solenoid without further testing
Correct answer: Check hydraulic fluid level and retarder control pressure
Verifying fluid level and control pressure confirms whether the retarder is receiving adequate hydraulic supply before condemning internal components.
310T Evaluation and Testing Process 3
When testing a truck's automatic transmission for slippage, the BEST method is to perform a: