California Emissions (Gen-Ii S)

Canister Purge Valve Check (Chart C-3):

Evaporative Purge Valve Control:

CIRCUIT DESCRIPTION
EVAP canister purge is controlled by a solenoid that allows manifold vacuum to purge the canister when deenergized. The ECM supplies a ground to energize the solenoid (purge "OFF"). The purge solenoid controlled by the ECM is pulse width modulated (turned "ON" and "OFF" several times a second). The duty cycle (pulse width) is determined by the amount of air flow and engine vacuum as determined by the MAP sensor input.

The duty cycle is calculated by the ECM and the output commanded when the following conditions have been met:
^ Engine run time after start more than 3 minutes.
^ Engine coolant temperature above 8O°C (176°F).
^ Vehicle speed above 15 mph.
^ Throttle at idle (about 3%).

Also, if the diagnostic "test" terminal is grounded with the engine stopped, the purge solenoid is deenergized (purge "ON").



TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. This checks to see if the solenoid is opened or closed. The solenoid is normally energized in this step, so it should be closed (energized).

2. Checks for a complete circuit. Normally there is ignition voltage on CKT 250 and the ECM provides a ground on CKT 428.

3. This completes a functional check by grounding the test terminal. This should normally de-energize the solenoid and allow the vacuum to drop (purge "ON").


DIAGNOSTIC AID

The canister purge solenoid is a normally open solenoid valve. Normal operation is as follows:

^ Ignition "ON", engine "OFF", diagnostic test terminal of ALDL NOT grounded - purge solenoid should be energized (valve closed).

^ Ignition "ON", engine "OFF", diagnostic test terminal of ALDL grounded - purge solenoid should NOT be energized (valve open).

^ An inoperative EVAP cannister purge system can cause a rich oxygen sensor (O2S) signal condition DTC 45. If the solenoid valve should become stuck open or the carbon canister become saturated, a continuous rich fuel condition may result.