System Diagnosis - Evaporative Emission Controls (EEC)

Chart C-3:

Canister Purge Wiring Diagram:

CANISTER PURGE VALVE CHECK

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.
If the diagnostic test terminal is not grounded, with the engine not running, or the following exist while the engine is running, the purge solenoid is de-energized:

1. The engine run time is more than three minute.
2. The coolant temperature is above 80~C (176~F).
3. The vehicle speed is above 15 mph.
4. The throttle is off-idle.

Note: If the diagnostic terminal is grounded, with the engine not running, the purge solenoid is de-energized, and purge is on.


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 terminal "A" of the solenoid connector, and the ECM provides the ground path to terminal "B" of the solenoid connector. A shorted solenoid could cause an open circuit in the ECM.
3. This completes the functional check by ungrounding the test terminal. This should normally de-energized the solenoid and allow the vacuum to drop.

NOTE: Once the test sequence is completed, clear codes and verify NO "SERVICE ENGINE SOON" light exists.

INCORRECT OPERATION MAY CAUSE:

1. Poor idle, stalling and poor driveability. Check for:

a. Inoperative or defective purge valve or solenoid
b. Damaged canister
c. Hoses split, cracked or not connected to the proper tubes
d. Pinched or plugged hose(s).