ASE4 Emission Control Systems

Question 1

The EGR (Exhaust Gas Recirculation) system primarily reduces which exhaust emission?

Accepted Answer

Oxides of nitrogen (NOx)

Answer

EGR introduces inert exhaust gases into the intake to lower peak combustion temperatures, which reduces NOx formation.

Question 2

A stuck-open EGR valve at idle will cause:

Accepted Answer

Rough idle and possible stalling

Answer

An EGR valve that stays open at idle dilutes the combustible mixture with exhaust gas, causing rough idle and potential stall.

Question 3

The EVAP (Evaporative Emission Control) system is designed to:

Accepted Answer

Prevent fuel vapor from escaping to the atmosphere

Answer

The EVAP system captures fuel vapors from the fuel tank and routes them to the intake to be burned rather than released into the air.

Question 4

A P0442 code (small EVAP leak detected) is set. The FIRST step in diagnosis is:

Accepted Answer

Perform a smoke test to locate the leak source

Answer

A smoke test is the most reliable and efficient method to locate small EVAP system leaks before replacing parts.

Question 5

An oxygen sensor that switches slowly between rich and lean is described as:

Accepted Answer

Lazy or degraded

Answer

A slow-switching O2 sensor is considered lazy or degraded, meaning it no longer responds quickly enough to support accurate closed-loop fuel control.

ASE4 - ASE Automobile Engine Performance Practice Test