P0446

SYSTEM DESCRIPTION
When running the DTC P0446 Evaporative Emission (EVAP) Vent System Performance diagnostic the powertrain control module (PCM ) monitors the fuel tank pressure (FTP) sensor. When vapor pressure rises to a specified value, the PCM commands the vent valve open, and monitors the FTP sensor signal. Pressure will increase rapidly because of the air allowed into the system. No increase or an increase below a specified rate indicates a restriction on the air inlet side. The PCM then commands the pressure switching solenoid closed. This blocks air from entering the tank side of the system. The PCM monitors the FTP sensor and looks for a decrease in the pressure rise. If there is no change in pressure the PCM concludes the pressure switching solenoid did not close. If the PCM does not detect an increase in pressure, or the rise in pressure does not change, a DTC P0446 will set.

CONDITIONS FOR RUNNING THE DTC
- The barometric pressure (BARO) is more than 75 kPa.
- The fuel level is between 25-75 percent.
- The ECT sensor and the intake air temperature (IAT) sensor are near the same temperature at engine start.
- The ECT sensor is at least 74°C (165°F) after engine warm up.

CONDITIONS FOR SETTING THE DTC
The pressure indicated in the EVAP canister and the fuel tank does not drop when the EVAP canister purge valve is ON.
OR:
The pressure indicated in the EVAP canister remains very low when compared to atmospheric pressure when the EVAP canister purge solenoid valve is OFF.

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
- The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

CONDITIONS FOR CLEARING THE MIL/DTC
- The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
- A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.
- A DTC can be cleared by using the scan tool Clear Information function.

DIAGNOSTIC AIDS
- If DTC P0446 is the only EVAP DTC set, the most likely cause is an inoperable EVAP canister vent solenoid, or pressure switching solenoid. Inspect the EVAP solenoids carefully for faulty connections and erratic operation.
- If the DTC cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
- Operating the vehicle in Check Mode will increase the ability of the powertrain control (PCM) module to detect engine control system malfunctions. Refer to Check Mode in Service Bay Test. Component Tests and General Diagnostics
- An intermittent malfunction may be caused by a fault in any of the EVAP solenoid electrical circuits. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 10-11:

Steps 6-10:

Steps 11-13:

Steps 14-17:

Steps 18-23:

The number below refers to the step number on the diagnostic table.
3. This step verifies that the DTC P0446 is captured in the freeze frame/failure record list. When multiple EVAP system DTCs are set, the DTC stored in the freeze frame/failure record is the best diagnostic starting point.
28. This step uses the EVAP Purge/Seal function to test for the correct operation of the EVAP canister vent solenoid, the pressure switching solenoid, and the purge solenoid. Using the EVAP Purge/Seal function also tests for leaks by allowing the technician to seal the system and monitor the FTP sensor.