Evaporative Emissions System: Testing and Inspection

EVAP Canister Purge Valve Circuit:

Circuit Description:
Canister purge is controlled by a solenoid that allows vacuum to purge the canister when energized. The PCM supplies a Pulse Width Modulated (PWM) ground to energize the solenoid (purge "ON").

If the [1][2]DLC diagnostic EVAP request terminal is grounded with the engine stopped or the following is met with the engine running, the purge solenoid is energized (purge "ON").

^ Engine run time after start more than 20 seconds on a warm engine or 2.5 minutes on a cold engine
^ Engine coolant temperature above 60°C (158°F)
^ Intake Air Temperature (IAT) is above 9.5°C (50°F)

EVAP Canister Purge Valve Check:

Test Description:
Numbers below refer to circled numbers on the diagnostic chart.

1. Checks to see if the solenoid is opened or closed. The solenoid is normally de-energized in this step, so it should be closed.

2. Completes functional check. This should normally energize the solenoid and allow vacuum to the gage (purge "ON").

Diagnostic Aids:
^ Inspect the canister for cracks or fuel saturation

^ Inspect fuel vapor lines from the fuel tank or intake for leaks, being disconnected or sharp bends blocking the flow of vapors.