CPT CPT Emissions & Environmental Standards 2

Question 1

When an OBD-II catalyst efficiency monitor sets a P0420 code, what specific condition triggers the fault?

Accepted Answer

The downstream O2 sensor's activity level approaches the upstream sensor's activity, indicating the catalyst is no longer storing oxygen effectively

Answer

P0420 is set when the catalyst efficiency monitor detects that the downstream sensor switches as frequently as the upstream sensor, meaning the catalyst has lost its oxygen storage capacity.

Question 2

What is the primary function of the Evaporative Emission Control (EVAP) system on modern US vehicles?

Accepted Answer

To capture fuel vapors from the tank and purge them into the intake for combustion rather than releasing them to the atmosphere

Answer

The EVAP system uses a charcoal canister to capture fuel vapors from the fuel tank and purges them through the intake manifold for combustion, preventing HC emissions.

Question 3

A CPT technician performs an EVAP large leak test and the system cannot achieve the required vacuum. After confirming the gas cap is good, what is the most systematic next step?

Accepted Answer

Use a smoke machine to pressurize the EVAP system and visually locate the leak source

Answer

A smoke machine introduces visible smoke into the sealed EVAP system, making even small leaks visible for precise diagnosis.

Question 4

Under US federal law, what is the minimum time an OBD-II system must operate (drive cycles) before an emissions-related readiness monitor is considered 'complete'?

Accepted Answer

It varies by monitor — some require one drive cycle, others require multiple specific conditions to be met

Answer

Different OBD-II monitors have different enabling conditions; some complete in one drive cycle while others (like catalyst and EVAP) require specific warm-up and drive patterns.

Question 5

What exhaust gas component does a two-gas analyzer measure to evaluate combustion efficiency at idle during a basic emission inspection?

Accepted Answer

Hydrocarbons (HC) and Carbon Monoxide (CO)

Answer

A basic two-gas analyzer measures HC (unburned fuel) and CO (incomplete combustion) as the primary indicators of combustion quality during idle emission tests.

CPT - Certified Performance Technician Practice Test

CPT - Certified Performance Technician Practice Test

CPT CPT Emissions & Environmental Standards 2