P0446

DTC P0446

SYSTEM DESCRIPTION




The evaporative emission (EVAP) system is used to store fuel vapors to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, the fuel tank pressure (FTP) sensor, the EVAP lines and hoses, the EVAP canister purge solenoid valve which is normally closed, the EVAP service port, the EVAP canister vent solenoid valve which is normally open, the fuel tank, and the powertrain control module (PCM). The PCM monitors the EVAP system for circuit faults in the FTP sensor, the EVAP canister purge solenoid valve and the EVAP canister vent solenoid valve circuits. The PCM also monitors the EVAP system for small and large leaks. During the DTC P0446 diagnostic, the EVAP canister purge solenoid valve is commanded to a fixed duty cycle, and the EVAP canister vent solenoid valve is commanded ON, closed, in order to build vacuum. Once vacuum is obtained, the EVAP canister vent solenoid valve is commanded OFF, open, and the vacuum should decrease rapidly. DTC P0446 sets when the vacuum decay is too slow, indicating a blocked vent system.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0135, P0452, P0453, P0502, P0503, P0601, P0602, P1621 are not set.
- The EVAP canister vent solenoid valve is commanded OFF, open.
- The EVAP canister purge solenoid valve is commanded to pulse width modulated (PWM), open.
- The fuel level is between 15-85 percent.
- The engine coolant temperature (ECT) and the intake air temperature (IAT) are between 4-30°C (30-86°F) at engine startup.
- The throttle position (TP) angle is between 10-35 percent.
- The DTC P0446 diagnostic is run once, usually for 30 seconds if no faults exist, during the EVAP diagnostic test after the above conditions have been met.

CONDITIONS FOR SETTING THE DTC
- If the FTP sensor voltage is less than 0.70 volts during the DTC P0446 diagnostic test indicating a blocked vent system, DTC P0446 will set.
- The above condition exists for longer than 1 minute and 40 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
- A short to ground causing the EVAP canister vent solenoid valve ON will cause the valve to close. This will cause DTC P0446 to set.
- The PCM uses the FTP sensor to detect the amount of vacuum pulled on the EVAP system during the leak diagnostic tests. Ensure that the fuel pressure sensor is not skewed by verifying the FTP sensor on the scan tool is between 2.35-2.85 volts with the ignition ON and the fuel cap removed.
- Inspect the following for causes of a blocked vent system:
- The EVAP canister vent solenoid valve blocked or a stuck valve
- A vent hose plugged, kinked, or pinched
- The EVAP canister restricted

TEST

Steps 1-6:

Steps 7-17:

Step 18: