ASE - Automotive Service Excellence Practice Test (A9: Light Vehicle Diesel Engines) 1

Question 1

A technician is diagnosing a light-duty diesel engine that cranks but will not start in cold weather. The glow plug indicator light does not illuminate. What is the MOST likely cause?

Accepted Answer

Failed glow plug control module

Answer

The glow plug control module energizes the glow plugs and signals the dashboard indicator. If the module fails, neither the glow plugs nor the lamp will activate, making cold starts difficult or impossible.

Question 2

A common-rail diesel fuel system is operating at lower than specified rail pressure at idle. Which component should the technician inspect FIRST?

Accepted Answer

Fuel pressure regulator/inlet metering valve

Answer

The inlet metering valve (or fuel pressure regulator) on the high-pressure pump controls the amount of fuel entering the pump, directly determining rail pressure. A sticking or failed regulator is the most common cause of low rail pressure at idle.

Question 3

White smoke from a diesel engine that persists after the engine reaches normal operating temperature is MOST likely caused by:

Accepted Answer

Incomplete combustion due to coolant entering the combustion chamber

Answer

Persistent white smoke after warm-up typically indicates coolant (water vapor) entering the combustion chamber through a blown head gasket or cracked cylinder head. Cold-start white smoke clears once the engine warms, but coolant intrusion continues indefinitely.

Question 4

A diesel technician performs a cylinder contribution (cut-out) test and finds that dropping cylinder #3 produces no change in engine roughness or RPM. What does this indicate?

Accepted Answer

Cylinder #3 injector is not contributing power to the engine

Answer

During a cylinder contribution test, a normally firing cylinder will cause a noticeable RPM drop when cut out. If cutting out a cylinder causes no change, that cylinder is not producing power, indicating a failed injector, no compression, or no fuel delivery to that cylinder.

Question 5

After replacing a diesel high-pressure fuel injector, the technician must perform which of the following procedures using a scan tool before returning the vehicle to service?

Accepted Answer

Injector quantity/trim code programming

Answer

Modern common-rail injectors have unique flow-rate calibration codes (IMA, C2I, or QR codes) that must be programmed into the ECM so the engine management system can compensate for individual injector flow characteristics and maintain correct fueling balance.

ASE Practice Test

ASE Practice Test

ASE - Automotive Service Excellence Practice Test (A9: Light Vehicle Diesel Engines) 1