ASE4 Emission Control Systems 3

Question 1

A knock sensor detects detonation. What does the ECM do in response?

Accepted Answer

Retards ignition timing to eliminate detonation

Answer

The ECM retards ignition timing when the knock sensor detects detonation, delaying combustion to reduce knock intensity.

Question 2

The EVAP large leak code P0455 is set. A smoke test finds smoke exiting from around the fuel cap. The correct repair is to:

Accepted Answer

Replace the fuel cap and retest

Answer

A leaking fuel cap is a common and simple cause of EVAP large leak codes; replacing the cap and verifying the seal corrects the fault.

Question 3

Which scan tool parameter BEST indicates whether the catalytic converter is working efficiently?

Accepted Answer

Comparison of upstream and downstream O2 sensor activity

Answer

Comparing upstream to downstream O2 sensor activity reveals how effectively the converter is smoothing exhaust gas composition variation.

Question 4

A vehicle has high NOx readings on an emissions test but passes HC and CO. The MOST likely cause is:

Accepted Answer

A faulty or clogged EGR system

Answer

High NOx with normal HC/CO points to insufficient EGR flow, which should be lowering combustion temperatures to suppress NOx.

Question 5

A continuous EVAP monitor detects a large leak during normal driving. The vent solenoid is commanded closed and the purge solenoid is commanded open. The system then monitors:

Accepted Answer

Vacuum decay in the EVAP system

Answer

The ECM seals the EVAP system and uses intake vacuum to create a vacuum in the tank, then monitors vacuum decay to detect leaks.

ASE4 - ASE Automobile Engine Performance Practice Test

ASE4 - ASE Automobile Engine Performance Practice Test

ASE4 Emission Control Systems 3