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

Coolant temperature sensor

Answer

Barometric pressure sensor

Answer

Fuel rail pressure sensor

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

Crank the engine to purge fuel

Answer

Disconnect the battery only

Answer

Loosen the fuel cap and start the engine

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

A clogged air filter

Answer

A faulty glow plug relay

Answer

Low coolant level

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 timing light

Answer

A compression-only gauge

Answer

A vacuum gauge

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

Engine oil viscosity

Answer

Transmission fluid level

Answer

Exhaust back pressure

Question 6

What does a fuel rail pressure that fails to reach commanded value during cranking most likely indicate?

Accepted Answer

A weak transfer pump, restriction, or failing high-pressure pump

Answer

A bad oxygen sensor

Answer

An open thermostat

Answer

A loose gas cap

Question 7

Before condemning an electronic diesel injector, a technician should first verify what?

Accepted Answer

Correct fuel supply, return, and rail pressure with no air in the system

Answer

Tire pressure

Answer

Coolant color

Answer

Serpentine belt tension