Canister Purge Solenoid: Description and Operation

EVAP PURGE VALVE OPERATION
If the EVAP purge valve does not seal properly, fuel vapors could enter the engine at an undesired time, causing driveability concerns. The PCM tests for this by commanding the vent valve closed and the pressure switching valve open causing a vacuum, in the entire EVAP system. The PCM continues to operate the purge valve until the vacuum is lowered to a specific point, at which time the purge valve is commanded closed. The PCM monitors the fuel tank pressure (FTP) sensor. If the PCM does not detect a drop in vacuum, or the vacuum increased beyond the specified limit, for two consecutive trips, the MIL will be illuminated, and a DTC P0441 will set.

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.