DTC P0446: EVAP Vent Solenoid Valve Control System: Description

The Evaporative Emission (EVAP) system is used to store fuel vapors to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, the Fuel Tank Pressure (FTP) sensor, the EVAP lines and hoses, the EVAP purge solenoid which is normally closed, the EVAP service port, the EVAP vent solenoid which is normally open, the fuel tank, and the PCM. The PCM monitors the EVAP system for circuit faults in the FTP sensor, the EVAP purge solenoid and the EVAP vent solenoid circuits. The PCM also monitors the EVAP system for small and large leaks. During the DTC P0446 diagnostic, the EVAP purge solenoid is commanded to a fixed duty cycle and the EVAP vent solenoid is commanded ON, closed, in order to build vacuum. Once vacuum is obtained, the EVAP vent solenoid is commanded OFF, open, and the vacuum should decrease rapidly. DTC P0446 sets when the vacuum decay is too slow, indicating a blocked vent system.