Evaporative Emissions System: Testing and Inspection

Chart C-3, Canister Purge Valve Check:

CIRCUIT DESCRIPTION:

Canister purge is controlled by a solenoid that allows manifold and/or ported vacuum to purge the canister when energized. The Electronic Control Module (ECM) supplies a ground to energize the solenoid (purge "ON"). The purge solenoid control by the ECM is turned "ON" or "OFF" under specific engine conditions. The purge solenoid is turned "ON" when all of the following conditions are met:

^ Engine rpm above 1500 rpm
^ Coolant temperature above 60°C (140°F)
^ Vehicle speed is above 15 mph

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. Checks to determine if solenoid was open due to electrical circuit problem or defective solenoid.

3. Completes functional check by grounding test terminal. This should normally energize the solenoid opening the valve which should allow the vacuum to drop (purge "ON").

VISUAL CHECK OF CANISTER

^ Cracked or damaged, replace canister.
^ Fuel leaking from bottom of canister vent hose, replace canister and check hoses.
^ Correct hose routing.

DIAGNOSTIC AIDS

Make a visual check of vacuum hose(s). Check throttle body for possible cracked, broken, or plugged vacuum hoses. Check engine for possible mechanical problem.

RESULTS OF INCORRECT OPERATION

Poor idle, stalling and poor driveability can be caused by:

^ Inoperative purge solenoid
^ Damaged canister
^ Hoses split, cracked and/or not connected to the proper tubes.

Evidence of fuel loss or fuel vapor odor can be caused by:

^ Liquid fuel leaking from fuel lines, or fuel pump
^ Cracked or damaged canister
^ Disconnected, misrouted, kinked, deteriorated or damaged vapor hoses, or control hoses.

If the solenoid is always open, the canister can purge to the intake manifold at all times. This can allow extra fuel at idle or during warm-up, which can cause rough or unstable idle, or too rich operation. If the solenoid is always closed, the canister can become over-loaded, resulting in fuel odor.