Circuit Description

Canister purge is controlled by a solenoid valve that allows manifold vacuum to purge the canister. The engine control module (ECM) supplies a ground to energize the solenoid valve (purge "ON"). The EVAP purge solenoid control is pulse-width modulated (PWM) or turned "ON" and "OFF" several times a second. The duty cycle (pulse width) is determined by engine operating conditions including load, throttle position, coolant temperature and ambient temperature. The duty cycle is calculated by the ECM and the output is commanded when the appropriate conditions have been met.