P0446

Engine Controls Schematics: MAF Sensor, EVAP System, EGR Valve:

SYSTEM DESCRIPTION
A RESTRICTED or BLOCKED EVAP VENT PATH is detected by monitoring fuel tank pressure during normal operation (EVAP vent valve/solenoid open, EVAP canister purge valve normal). With the EVAP vent valve open, vacuum level in the system should be very low unless the vent path is blocked. A blockage can be caused by the following conditions:
^ Faulty EVAP vent valve (stuck closed)
^ Plugged kinked or pinched vent hose
^ Shorted EVAP vent valve driver circuit
^ Plugged EVAP canister

If any of the conditions described above are present, DTC P0446 will set.

CONDITIONS FOR RUNNING THE DTC
^ No TP sensor, ODM, IAT sensor, or MAP sensor DTCs set.
^ All conditions for P0440 and P0442 have been met and passed.
^ Startup engine coolant temperature is not more than 4°C and 30°C (40°F and 86°F).
^ Startup engine is not more than 8°C (14°F).
^ Startup Intake air temperature not more than 2°C and 30°C (40°F and 86°F).
^ Startup intake air temperature not more than 2°C (4°F).
^ Fuel tank level is between 15 percent and 85 percent.
^ BARO is more than 75 kPa.

CONDITIONS FOR SETTING THE DTC
^ Fuel tank pressure is less than -10 inch H2O.
^ The condition is present for at least 30 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the MIL during the first trip in which the diagnostic runs and fails.
^ If equipped with traction control, the PCM will command the EBTCM via the serial data circuit to turn OFF traction control and illuminate the TRACTION OFF lamp.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

IMPORTANT: Although this diagnostic is considered type A, it acts like a type B diagnostic. Whenever the EVAP diagnostics report that a system has passed, or if the battery has been disconnected, the diagnostic must fail during 2 consecutive cold start trips before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports to the diagnostic executive immediately.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
Inspect for the following:
^ Kinked, pinched or plugged vent hose
^ Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

TEST DESCRIPTION

Steps 1 - 5:

Steps 6 - 12:

The numbers below refer to the step numbers on the diagnostic table:
1. The Powertrain On-Board Diagnosis (OBD) System Check prompts you to the basic checks and store the Freeze Frame and Failure Records Data on the scan tool if applicable.
2. If a EVAP vent valve or EVAP purge valve electrical malfunction is present, the purge system will not operate correctly. Repairing the electrical malfunction that caused the additional DTC to set will very likely correct the condition that set this DTC.
3. Inspects for a fuel tank pressure sensor stuck high condition. The fuel tank pressure must be relieved by removing the canister line from the fuel tank or EVAP canister. The fuel fill cap will not relieve the tank pressure due to a check valve in the filler neck. The check valve seals when pressure is applied to prevent vapor from escaping through the filler neck. The scan tool should read within 1.0 inch H2O of the specified value.
4. Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes. The EVAP station is pressurizing a sensor that normally reads vacuum. The scan tool reads high pressure at 0 volts and high vacuum at 5 volts. The scan tool can only read a max pressure of 6.0 inch of H2O (0 volts). However the EVAP service station can pressurize the system to much higher pressures. The scan tool value should be within 0.5 inch H2O of the specified value.
5. Inspects for a plugged or stuck closed EVAP vent valve. The value should decrease to within 1.0 inch HG of the specified value.