ASE4 Emission Control Systems 2

Question 1

A P0401 code (insufficient EGR flow) is stored. Before replacing the EGR valve, the technician should check:

Accepted Answer

The EGR passages for carbon buildup restricting flow

Answer

EGR passages and ports frequently become clogged with carbon deposits, causing insufficient flow without the EGR valve itself being faulty.

Question 2

The AIR (Secondary Air Injection) system is MOST active:

Accepted Answer

Immediately after cold engine startup

Answer

The AIR system pumps fresh air into the exhaust stream right after cold startup to help oxidize unburned HC and CO and rapidly heat the catalyst.

Question 3

Which emission is directly measured by the upstream (pre-catalyst) oxygen sensor?

Accepted Answer

Oxygen content in the exhaust stream

Answer

The upstream O2 sensor measures the oxygen content of exhaust gases, which the ECM uses to calculate rich/lean condition and adjust fuel delivery.

Question 4

A vehicle fails an OBD-II plug-in emissions test. The technician is told two monitors are 'not ready.' The BEST approach is to:

Accepted Answer

Perform the appropriate OBD-II drive cycles to set the incomplete monitors

Answer

Incomplete monitors must be set by performing the specific drive cycles that allow the ECM to run those self-tests.

Question 5

Excess hydrocarbons (HC) in the exhaust are MOST commonly caused by:

Accepted Answer

Incomplete combustion from misfires or an overly rich mixture

Answer

Unburned fuel in the exhaust is the primary source of HC emissions, typically caused by misfires, a rich mixture, or poor combustion.

ASE4 - ASE Automobile Engine Performance Practice Test