Chart C-3 EVAP Canister Purge Valve Check

Chart C-3:

Evaporative Emission (EVAP) Canister Purge Valve Check:

CIRCUIT DESCRIPTION
Canister purge is controlled by a valve that allows ported vacuum to purge the Evaporative Emissions (EVAP) canister when energized. The Powertrain Control Module (PCM) supplies a ground to energize the valve (purge "ON"). The purge solenoid valve control by the PCM is pulse width modulated (turned "ON" and "OFF" several times a second). The duty cycle (pulse width) is determined by "Closed Loop" feed back from the Oxygen Sensor (O2S). The duty cycle is calculated by the PCM and the output is commanded when the following conditions have been met:

^ Engine run time is greater than 30 seconds if engine coolant temperature is above 56°C (133°F).
OR
^ Engine run time is greater than 185 seconds if engine coolant temperature is below 56°C (133°F).

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Checks if the valve is opened or closed. The valve is normally de-energized in this step, so it should be closed.
2. Checks to determine if valve was open due to electrical circuit problem or defective valve.
3. This should normally energize the valve, opening the valve should allow the vacuum to drop (purge "ON").

DIAGNOSTIC AIDS
^ Make a visual check of vacuum hose(s).
^ Check throttle body for possible cracked, broken, or plugged vacuum block.
^ Check engine for possible mechanical problem.