Evaporative Emissions System: Testing and Inspection

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 fuel vapor 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 exists while the engine is running, the purge solenoid is de-energized:

1. The engine run time is more than one minute.
2. The coolant temperature is above 65~C (149~F).
3. The engine is not in decel fuel cuttoff.
4. The system is in "Closed Loop".



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).




2. Evidence of fuel loss or fuel vapor odor. Check for:

a. Liquid fuel leaking from fuel lines, fuel pump, or injectors
b. Cracked or damaged canister
c. Inoperative canister control valve
d. Disconnected, misrouted, kinked, deteriorated or damaged vapor hoses, or control hoses
d. If the solenoid is always open, the canister may purge all the time. This can allow extra fuel at idle or during warm-up, which can cause a rough idle or a rich operation
e. If the solenoid is always closed, the canister can become over-loaded, resulting in fuel odor.