Circuit Description

This test is used to determine if the Evaporative Emission (EVAP) solenoid is open (passing vacuum) when the PCM is commanding it closed or if the EVAP switch or circuit is open. The EVAP switch is a normally closed switch mounted in the vacuum line between the EVAP canister and the EVAP solenoid. The switch opens when vacuum (7.5 in Hg) from engine draws the evaporative emissions from the EVAP canister through the EVAP solenoid and into the throttle body.

The PCM monitors the state of the EVAP vacuum switch to determine if EVAP solenoid is open and allowing vacuum to pass. PCM accomplishes this by monitoring the amount of time the EVAP vacuum switch is continuously open or closed with purge off. If switch is open during the test conditions for 9 consecutive seconds, DTC will set.