P0446

EVAP Vent System Performance:

P0446- EVAP VENT SYSTEM PERFORMANCE
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 EVAP 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.

DTC PARAMETERS
DTC P0446 will set it fuel tank pressure indicates less than 1.30 volts (less than -11.21 mmHg (-6.00 in H2O) during phase A of the EVAP diagnostic system test or less than 2.02 volts (less than -4.5 mmHg (-2.41 in H2O) during phase C of the EVAP diagnostic test indicating a blocked vent system when:
^ Condition exists for 15 seconds for phase A or condition is present by the end of phase C
^ EVAP purge solenoid is commanded to a certain duty cycle
^ EVAP vent solenoid is commanded Off
^ Engine is at idle
^ Vehicle speed 0 mph
^ Engine load is less than 35%
^ MAP is less than 40 kPa
^ Battery voltage is greater than 11.0 volts
^ Start-up ECT is between 8°C and 50°C (46° and 167°F)
^ IAT is between 8°C and 50°C (46° and 122°F)
^ Long term fuel trim cells learned (if not learned, engine must run longer than 16 minutes and 45 seconds)
^ Fuel level is between 6 and 48L (1.6 and 12.7 gallons)
^ No ECT, EVAP purge solenoid, EVAP vent solenoid, fuel tank pressure. idle speed, HO2S. throttle actuator, TP sensor or vehicle speed DTCs have been set.

DTC P0446 diagnostic runs once during phase A and phase C of the EVAP diagnostic test once per ignition cycle.

If an EVAP diagnostic test is aborted due to changing enable criteria, the ECM will attempt to rerun the EVAP diagnostic test up to three times per ignition cycle.

P0446 is a type B DTC

DIAGNOSTIC AIDS

IMPORTANT: If any EVAP system DTC is set, EVAP special functions on Scan tool will not be allowed. Clear DTCs before performing these tests.

IMPORTANT: The ECM uses the fuel tank pressure sensor to detect the vapor in the fuel tank during all parts of the EVAP diagnostic system test. Make sure the fuel tank pressure sensor is not skewed by verifying FUEL TANK PRESS. SENSOR on Scan tool is between 2.35 and 2.85 volts with ignition On and engine Off and fuel cap removed.

Refer to EVAP System Description" at the end of this section for a complete EVAP diagnostic test description. Possible causes of a blocked EVAP vent system:
^ EVAP vent solenoid blocked or stuck valve
^ EVAP vent hose from EVAP canister to EVAP vent line or EVAP hose at EVAP vent box kinked or pinched EVAP canister restricted