Circuit Description

This test determines if the Evaporative Emission (EVAP) control solenoid is open when the PCM is commanding it to open. PCM does this by monitoring EVAP vacuum switch which is a normally closed switch. Switch is located in vacuum line between EVAP canister and EVAP solenoid. When the switch opens, vacuum from the engine draws evaporative emissions from EVAP canister into throttle body.

The state of the EVAP switch is monitored by the PCM to determine if EVAP solenoid is open and passing vacuum. The PCM accomplishes this by monitoring the amount of time the EVAP switch is continuously open or closed during purge. The the test conditions are met, PCM starts a timer, which will be reset when the switch transitions open or closed or vice versa. If switch remains closed for 9 seconds continuously, DTC will set. If switch remains open for 2 seconds continuously, test is passed.