Evaluation and Testing Process Flashcards

When testing a truck's automatic transmission for slippage, the BEST method is to perform a:

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.

During functional testing of a truck's ABS system, the amber ABS warning lamp remains illuminated after the vehicle exceeds 6 mph. This indicates:

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.

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:

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.

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:

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.

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:

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.

When evaluating a Class 8 truck's fifth wheel coupling, a technician should test jaw engagement by:

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.

During evaluation of a hydraulic retarder on a coach, the retarder provides no braking effort when engaged. The FIRST test should be to:

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.