Circuit Description

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.

When running the DTC P0446 Evaporative Emission (EVAP) Vent System Performance diagnostic, Powertrain Control Module (PCM), monitors Fuel Tank Pressure (FTP) sensor. When vapor pressure rises to a specified value, PCM commands the vent valve open, and monitors FTP sensor signal. Pressure will increase rapidly because of the air allowed into the system. No increase or an increase below a specified rate indicates a restriction on the air inlet side. PCM then commands the pressure switching solenoid closed. This blocks air from entering the tank side of the system. PCM monitors FTP sensor and looks for a decrease in pressure rise. If there is no change in pressure PCM concludes pressure switching solenoid did not close. If PCM does not detect an increase in pressure, or rise in pressure does not change, a DTC P0446 will set.