Evaporative Emissions System: Testing and Inspection

Chart C-3:

Wiring Diagram Canister Purge Solenoid:

CIRCUIT DESCRIPTION:

The canister purge is controlled by a solenoid that allows manifold vacuum to purge the canister when de-energized. The ECM controls the ground to power the solenoid. The purge solenoid is controlled by a pulse width modulation signal from the ECM. The duty cycle is determined by the amount of air flow, and by the MAP sensor input.

If the diagnostic test terminal is grounded with the engine stopped, the purge solenoid is de-energized. The duty cycle is calculated by the ECM when the following conditions exists:

^ The engine run time is more than three minutes.
^ The coolant temperature is above 80~C or 176~F.
^ The vehicle speed is above 15 mph.
^ The throttle is off-idle (approximately 3%).


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 (energized).

2. This checks for a complete circuit. Normally there is ignition voltage on circuit 39 of the solenoid connector, and the ECM provides the ground path on circuit 428.

3. This completes the functional check by grounding the test terminal. This should normally de-energized the solenoid and allow the vacuum to drop.



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.