Evaporative Emissions System: Testing and Inspection

Chart C-3:

Chart C-3 Wiring Diagram:

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:

^ The engine run time is more than 65 seconds.
^ 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.

DIAGNOSTIC AIDS:

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