Note. For circuit reference, see DTC P0441 schematic.
Circuit Description
The EVAP switch is a normally closed switch mounted in the vacuum line between the EVAP canister and the EVAP solenoid. The switch open 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. This test checks the EVAP switch and circuit for an open condition (signal high) before the engine is started.