Evaporative Emissions System: Testing and Inspection

Chart C-3:

Chart C-3 Wiring Diagram:

CIRCUIT DESCRIPTION:

The canister purge is controlled by a solenoid that allows vacuum to purge the fuel vapor canister when energized. The ECM supplies a ground to power the solenoid. If the diagnostic test terminal is grounded with the engine not running, or the following conditions exists with the engine running, the purge solenoid is energized (purge "ON").

^ The engine run time is more than 30 seconds.
^ The coolant temperature is above 60~C (158~F).
^ "Closed Loop" operation.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This checks to see if the solenoid is opened or closed. It should be closed (de-energized).

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

3. Checks for an open in circuits 428 or 639.

DIAGNOSTIC AIDS:

^ Inspect the canister for cracks or fuel saturation.

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