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

Faulty crankshaft position sensor

Answer

Plugged fuel filter

Answer

Low compression in cylinder #1

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

High-pressure fuel injectors

Answer

Low-pressure lift pump

Answer

Diesel particulate filter differential pressure sensor

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

An overly rich air-fuel mixture

Answer

Excessive lubricating oil consumption

Answer

A clogged diesel oxidation catalyst (DOC)

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

Cylinder #3 is over-fueling compared to other cylinders

Answer

The high-pressure fuel pump is weak

Answer

Cylinder #3 has excessive compression

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

Throttle position sensor relearn

Answer

Diesel oxidation catalyst regeneration

Answer

Crankshaft reluctor wheel relearn

Question 6

A diesel vehicle equipped with a selective catalytic reduction (SCR) system has a MIL on and a DTC for low NOx conversion efficiency. Which component is MOST likely at fault?

Accepted Answer

Diesel exhaust fluid (DEF) dosing injector — clogged or failed

Answer

Diesel particulate filter (DPF) — full of soot

Answer

Exhaust gas recirculation (EGR) valve — stuck open

Answer

Turbocharger wastegate — stuck closed