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

The three-way catalytic converter uses platinum, palladium, and rhodium to oxidize hydrocarbons (HC) and carbon monoxide (CO) and reduce nitrogen oxides (NOx) simultaneously.

Question 2

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

Accepted Answer

Catalyst Monitor

Answer

The Catalyst Monitor compares switching frequency and voltage readings between upstream and downstream oxygen sensors to determine if the converter is storing and releasing oxygen effectively.

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

EGR reduces NOx emissions by reintroducing a metered amount of exhaust gas into the intake, lowering combustion temperatures that drive nitrogen and oxygen to combine into NOx.

Question 4

What does a P0420 DTC indicate on a GM vehicle?

Accepted Answer

Catalyst system efficiency below threshold (Bank 1)

Answer

P0420 indicates the PCM has detected that the Bank 1 catalytic converter's oxygen storage efficiency has dropped below the OBD-II threshold, signaling converter degradation.

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

A vacuum leak allows unmetered air past the MAF sensor, causing the PCM to see a lean condition; the PCM compensates with positive fuel trim until a P0171 is set when the limit is exceeded.

(GM) General Motors Certified Practice Test

(GM) General Motors Certified Practice Test

GM Fuel Systems and Emissions 2