ASE Test Electronic Diesel Engine Diagnosis 3

Question 1

An electronic diesel sets a DTC for low boost pressure under load. Which component should be inspected first?

Accepted Answer

Turbocharger, boost sensor, and charge-air piping for leaks

Answer

Low boost codes are commonly caused by turbo wear, a faulty boost sensor, or leaks in the charge-air (intercooler) piping.

Question 2

What is the purpose of the manifold absolute pressure (MAP) sensor on a turbo diesel?

Accepted Answer

To monitor boost/intake pressure for fueling and EGR control

Answer

The MAP sensor reports intake manifold (boost) pressure so the ECM can manage fueling and emissions controls.

Question 3

A diesel exhibits white smoke at idle when cold but clears as it warms. What is the most likely benign cause?

Accepted Answer

Incomplete combustion / unburned fuel during cold operation

Answer

Cold-start white smoke that clears with warm-up is typically unburned fuel from incomplete combustion before the engine reaches operating temperature.

Question 4

When verifying a MAF sensor concern on a modern diesel, what symptom commonly results from a contaminated MAF?

Accepted Answer

Reduced power, derate, and incorrect EGR/fueling

Answer

A contaminated mass airflow sensor reports incorrect airflow, causing power loss, derate, and faulty EGR/fuel calculations.

Question 5

Which scan tool data PID best helps diagnose an EGR valve that is sticking open?

Accepted Answer

Commanded vs. actual EGR position

Answer

Comparing commanded EGR position to actual feedback reveals a valve that fails to follow commands, such as sticking open.

ASE Practice Test

ASE Practice Test

ASE Test Electronic Diesel Engine Diagnosis 3