DTC P0446: EVAP Vent System Performance: Description

The Evaporative Emission (EVAP) system is used to store fuel vapors as to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, Fuel Tank Pressure (FTP) sensor, EVAP lines and hoses, EVAP purge solenoid (normally closed), EVAP service port, EVAP vent solenoid (normally open) and fuel tank. The ECM monitors the EVAP system for circuit faults in the EVAP purge solenoid, EVAP vent solenoid and FTP sensor circuits. The ECM also monitors the EVAP system for leaks (between EVAP vent and purge solenoid). When certain conditions have been met, the ECM will perform an EVAP diagnostic test at idle with no vehicle speed, which will require a five consecutive phase ("A", "B", "C", "D" and "E") test. DTC P0446 will set if too much vacuum is present with the EVAP vent solenoid commanded OFF during Phase "A" or Phase "C" of the EVAP diagnostic system test indicating a blocked EVAP vent system.