Circuit Description

Evaporative Emission (EVAP) canister purge valve allows manifold vacuum to purge canister. Powertrain Control Module (PCM) supplies a ground to energize the solenoid valve (purge on). EVAP canister purge valve is 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. Duty cycle is calculated by PCM and the output is commanded when appropriate conditions have been met.

The system checks for conditions that cause EVAP system to purge continuously by commanding EVAP vent solenoid ON and EVAP canister purge valve OFF. If fuel tank vacuum level increases during the test, a continuous purge flow condition is indicated.