Pressure Switching Solenoid Operation

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

The EVAP pressure switching solenoid is OFF, closed during engine warm up. with the pressure switching solenoid closed, vacuum pressure is blocked from entering the fuel tank and pressure in the fuel tank will rise. The FTP sensor will see a significant decrease in pressure in the tank only when the pressure switching solenoid is ON, OPEN, during a purge event. If the pressure switching solenoid malfunctions during this portion of the EVAP system operation, DTC P0440 and DTC P0441 may set.

During the DTC P0446 portion of the EVAP system diagnostic the pressure switching solenoid is ON. This enables the FTP sensor to see a rapid decrease in vacuum, when the air from the EVAP vent solenoid enters the tank. When the PCM commands the pressure switching solenoid OFF, the FTP sensor should see the vacuum pressure stabilize and not continue to decrease. If the FTP sensor still sees a significant decrease in vacuum, the PCM concludes the solenoid did not close and sets DTC P0446.