ASE Test Electronic Diesel Engine Diagnosis 2

Question 1

A diesel engine cranks but will not start, and a scan tool shows zero RPM signal during cranking. Which sensor is the most likely cause?

Accepted Answer

Crankshaft position sensor

Answer

The crankshaft position sensor provides the RPM signal the ECM needs to time injection, so a no-RPM-during-cranking reading points to it.

Question 2

When diagnosing a high-pressure common rail (HPCR) system, what is the safest first step before disconnecting any line?

Accepted Answer

Relieve fuel rail pressure and let the engine cool

Answer

Common rail systems hold extremely high pressure that can cause injection injury, so rail pressure must be relieved and the engine allowed to cool first.

Question 3

A technician finds excessive injector return (back-leakage) fuel on a common rail engine. What does this typically indicate?

Accepted Answer

Worn or leaking injectors

Answer

Excessive return flow from one or more injectors indicates internal injector wear or leakage that bleeds off rail pressure.

Question 4

Which diagnostic tool is used to measure individual cylinder contribution on an electronically controlled diesel?

Accepted Answer

Cylinder balance / contribution test via scan tool

Answer

A scan tool cylinder balance (contribution) test cuts injectors individually to reveal weak cylinders.

Question 5

A glow plug warning lamp stays on and the engine is hard to start cold. What should be checked first?

Accepted Answer

Glow plug circuit and relay operation

Answer

A glow plug lamp fault with hard cold starts points directly to the glow plug circuit, relay, or individual plugs.

ASE Practice Test

ASE Practice Test

ASE Test Electronic Diesel Engine Diagnosis 2