Evaporative Emissions System: Testing and Inspection

Chart C-3:

EVAP System Flow:

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 supplies a ground to power the solenoid (purge "ON"). 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 "CLOSED LOOP" feed-back from the oxygen sensor. The duty cycle is calculated by the ECM and the output commanded when the following conditions have been met:

^ The engine run time is more than 65 seconds.
^ The coolant temperature is above 56°C (133°F).

Also, if the diagnostic test terminal is grounded with the ignition "ON," engine not running, the purge solenoid is energized (purge "ON").

DIAGNOSTIC AIDS:
Make a visual check of vacuum hoses. Check throttle body for possible cracked, broken, or plugged vacuum block. Check engine for possible mechanical problem.