Federal Emissions

Canister Purge Valve Check (Chart C-3):

Purge Solenoid Circuit Diagram:

CIRCUIT DESCRIPTION
The canister purge is controlled by a solenoid that blocks vacuum to the fuel vapor canister when energized. The solenoid gets power when the ignition is turned "ON" and the ECM controls the ground circuit.


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.