Evaporative Emissions System: Description and Operation

Evaporative Emissions Control System Schematic:

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 has been running a specified amount of time.
^ The engine is warm.

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