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

The catalytic converter efficiency

Answer

The oxygen sensor switching speed

Answer

The fuel pressure regulator

Question 2

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

Accepted Answer

Immediately after cold engine startup

Answer

At highway cruise speeds

Answer

During wide-open throttle acceleration

Answer

When the EGR valve is open

Question 3

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

Accepted Answer

Oxygen content in the exhaust stream

Answer

NOx concentration

Answer

Hydrocarbon content

Answer

Carbon monoxide levels

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

Replace the catalytic converter and oxygen sensors

Answer

Clear all DTCs and retest immediately

Answer

Inspect and replace the EGR valve

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

High combustion temperatures

Answer

Advanced ignition timing

Answer

High EGR flow rates

Question 6

A scan tool shows the EVAP purge solenoid is commanded ON but the fuel trims show no change. This indicates:

Accepted Answer

The purge solenoid is not opening or the canister is empty/disconnected

Answer

The EVAP canister is fully purged and working normally

Answer

A vacuum leak downstream of the purge solenoid

Answer

The EVAP system is working correctly