Evaporative Emissions System: Testing and Inspection

Chart C-3:

EVAP Wiring Diagram:

CIRCUIT DESCRIPTION
The canister purge is controlled by a solenoid that allows manifold vacuum and/or ported vacuum to purge the canister when energized. The Powertrain Control Module (PCM) supplies a ground to energize the valve (purge "ON"). The purge solenoid valve, controlled by the PCM, is pulse width modulated (turned "ON" and "OFF" several times a second). The duty cycle is determined by CLOSED LOOP feed-back from the oxygen sensor. The duty cycle is calculated by the PCM and the output commanded when the following conditions have been met:
1. The engine run time is more than 65 seconds.
2. The coolant temperature is above 56°C (133°F).

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.
1. This checks to see if the solenoid valve is opened or closed. The solenoid valve is normally de-energized in this step, so it should be closed.
2. This determines if the solenoid valve was open due to an electrical circuit problem or a defective solenoid.
3. This completes the functional check by commanding solenoid valve "ON." This should normally energize the solenoid valve opening the valve which should allow the vacuum to drop (purge "ON").

DIAGNOSTIC AIDS
Perform 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.