GM Fuel Systems and Emissions 2

Question 1

What is the role of the catalytic converter on a GM vehicle in reducing emissions?

Accepted Answer

Oxidize HC and CO and reduce NOx through chemical reactions using precious metal catalysts

Answer

Increase exhaust back pressure to improve low-end torque

Answer

Filter particulate matter from the exhaust stream using a ceramic wall-flow filter

Answer

Recirculate exhaust gases back into the intake manifold

Question 2

Which OBD-II monitor specifically evaluates catalytic converter efficiency on GM vehicles?

Accepted Answer

Catalyst Monitor

Answer

Oxygen Sensor Monitor

Answer

Comprehensive Components Monitor

Answer

EGR System Monitor

Question 3

On GM vehicles with Exhaust Gas Recirculation (EGR), what is the primary emission the EGR system is designed to reduce?

Accepted Answer

Nitrogen oxides (NOx)

Answer

Hydrocarbons (HC)

Answer

Carbon monoxide (CO)

Answer

Carbon dioxide (CO2)

Question 4

What does a P0420 DTC indicate on a GM vehicle?

Accepted Answer

Catalyst system efficiency below threshold (Bank 1)

Answer

Upstream oxygen sensor circuit malfunction

Answer

EVAP system large leak detected

Answer

Fuel pressure sensor out of range

Question 5

On a GM vehicle, what condition would cause the PCM to set a P0171 (System Too Lean, Bank 1) diagnostic trouble code?

Accepted Answer

A large vacuum leak causing unmetered air to enter the intake

Answer

Fuel injector stuck open causing excessive fuel delivery

Answer

A rich exhaust condition from a flooded engine

Answer

Downstream oxygen sensor reading 0.8V continuously

Question 6

What is the purpose of the Secondary Air Injection (AIR) system used on some GM engines during cold start?

Accepted Answer

Pump fresh air into the exhaust stream to oxidize unburned HC and CO during warm-up

Answer

Provide additional air to the fuel injectors to lean out the mixture at idle

Answer

Pressurize the fuel system above normal operating pressure for cold-start enrichment

Answer

Supply air to the EGR valve to promote exhaust gas mixing

Question 7

On GM GDI engines, what is a commonly recommended maintenance procedure to address carbon buildup on intake valves?

Accepted Answer

Perform an intake valve cleaning using walnut blasting or approved chemical decarbonization

Answer

Replace the fuel filter every 15,000 miles to improve atomization

Answer

Increase injector pulse width via PCM calibration to wash valves with extra fuel

Answer

Replace the oxygen sensor to reset adaptive fuel trims and improve combustion