Evaporative Emissions System: Testing and Inspection

Chart C-3:

Canister Purge Valve Wiring Diagram:

CANISTER PURGE VALVE CHECK

CIRCUIT DESCRIPTION:

The canister purge is controlled by a solenoid that allows manifold vacuum and/or ported vacuum to purge the fuel vapor canister when energized. The ECM controls the ground to power the solenoid. The duty cycle is determined by closed loop feed back from the oxygen sensor. If the diagnostic test terminal is grounded with the engine not running, the purge solenoid is energized.
The duty cycle is calculated by the ECM when the following conditions exists:

1. The engine run time is more than 65 seconds.
2. The coolant temperature is above 56~C (132.8~F).




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. This determines if the solenoid was open due to an electrical circuit problem or a defective solenoid.
3. This completes the functional check by grounding the test terminal. This should normally energize 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.


DIAGNOSTIC AIDS:

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




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.