EVAP Vent Valve Operation

If the EVAP vent system is restricted the fuel vapors will not be properly purged. When the vapor pressure rises to a specified point, the PCM commands the vent valve OFF, OPEN, and monitors the fuel tank pressure (FTP) sensor signal. Vacuum will decrease rapidly because of the air allowed into the system. No decrease in vacuum or a decrease below a specified rate indicates a restriction on the air inlet side. If the PCM does not detect a decrease in vacuum, or the vacuum level does not change for two consecutive trips, the MIL will be illuminated, and a DTC P0446 will set.