P0446

Schematic:

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 sensor, EVAP lines and hoses, EVAP purge solenoid (normally closed), EVAP service port, EVAP vent solenoid (normally open) and fuel tank. The PCM monitors the EVAP system for circuit faults in the fuel tank pressure sensor, EVAP purge solenoid and EVAP vent solenoid circuits. The PCM also monitors the EVAP system for small and large leaks. During DTC P0446 diagnostic, the EVAP purge solenoid is commanded On (open) 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 and the vacuum should decrease rapidly. DTC P0446 sets when the vacuum decay is too slow indicating a blocked vent system.

DTC PARAMETERS
DTC P0446 will set if EVAP system releases vacuum too slow during the diagnostic test indicating a blocked vent system when:
^ EVAP purge solenoid is commanded On (open)
^ EVAP vent solenoid is commanded Off (open)
^ Engine run time is greater than 2 seconds
^ Fuel tank level is between 15 and 85% full
^ Baro is greater than 81 kPa
^ ECT and IAT at engine start-up are between 50 and 32°C (41° and 90°F)
^ ECT and IAT are within 10°C (50°F) of each other
^ No ECT; fuel tank pressure, IAT, MAP or VSS DTCs have been set

DTC P0446 diagnostic is run once during the EVAP diagnostic test once the above conditions have been met.

DTC P0446 diagnostic may also run during initial key-up. The diagnostic runs at this time only when strict operating parameters have been met. Under most conditions, the test will run during the regular EVAP diagnostic test.

DTC P0446 is a type A DTC.

DIAGNOSTIC AIDS

IMPORTANT:
^ If DTC P0447 is set, diagnose that DTC first. A short to ground causing the EVAP vent solenoid On, will cause the vent valve to close. This will cause DTC P0446 to set.
^ The PCM uses the fuel tank pressure sensor to detect the vacuum decay of the EVAP vent solenoid diagnostic. Make sure the fuel pressure sensor is not skewed by verifying FUEL TANK PRESSURE on Scan tool is between 1.3 and 1.7 volts with ignition On and fuel cap removed.

Check the following for causes of a blocked vent system:
^ EVAP vent solenoid blocked or stuck valve
^ Vent hose plugged, kinked or pinched
^ EVAP canister restricted