P0446

Diagnostic Chart:

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.

DTC PARAMETERS
DTC P0446 will set if fuel tank pressure indicates greater than 2.94 volts (less than -13.5 mmHg (-7.23 in H2O)) during phase A of the EVAP diagnostic system test or greater than 1.57 volts (less than -.69 mmHg (-0.37 in H2O)) during phase C of the EVAP diagnostic test indicating a blocked vent system when:
^ Condition exists for 20 seconds for phase A or condition is present for longer than 1.5 seconds during 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%
^ Main relay voltage is greater than 10.0 volts
^ ECT at engine startup is between 4°C and 55°C (40° and 131°F)
^ IAT is between 4°C and 60°C (40° and 140°F)
^ Fuel tank pressure must be within -13.5 to 6.75 mmHg (-7.23 to 3.61 in H2O) to enable test
^ Long term fuel trim cells learned (if not learned, engine must run longer than 16 minutes and 45 seconds)
^ Fuel level is between 9.1 and 50.7 L (2.4 and 13.4 gallons)
^ No ECT, EVAP purge solenoid, EVAP vent solenoid, fuel tank pressure, idle speed, HO2S, MAF, system voltage, throttle actuator, TP sensor or vehicle speed
DTCs have been set.

The entire EVAP diagnostic test will take about 16 seconds to complete when no errors have been detected. If the P0446 diagnostic fails, the rest of the EVAP diagnostic test is aborted and not run again in the ignition cycle.

If an EVAP diagnostic test is aborted due to changing enable criteria, the ECM will run the entire EVAP diagnostic test up to 10 times per ignition cycle.

P0446 is a type B DTC.

DIAGNOSTIC AIDS

IMPORTANT:
^ If DTC P0440, P0442, P0446 or P0496 is set, EVAP special functions on Scan tool will not be allowed. Clear DTCs before performing these tests.
^ 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 FTP SENSOR on Scan tool is between 1.40 and 1.60 volts with ignition On and engine Off.

Refer to "EVAP System Description" for a complete EVAP diagnostic test description.

Possible causes of a blocked EVAP vent system:
^ EVAP vent solenoid blocked or stuck valve
^ EVAP vent foam filter for a blocked condition (filter can be checked by removing EVAP canister end cover near EVAP vent solenoid).
^ EVAP vent hose from EVAP canister to fuel filler neck kinked or pinched
^ EVAP canister restricted