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 canister when de-energized. The ECM controls the ground to power the solenoid. The purge soleniod is controled 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:

1. The engine run time is more than three minutes.
2. The coolant temperature is above 80~C or 176~F.
3. The vehicle speed is above 15 mph.
4. 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 terminal "A" of the solenoid connector, and the ECM provides the ground path at terminal "B" of the solenoid connector. A shorted solenoid could cause an open circuit in the ECM.
3. This completes the functional check by grounding 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.