P0446

CIRCUIT DESCRIPTION
A restricted or blocked evaporative emission (EVAP) vent path is detected by the control module commanding the purge valve ON, open, and the vent valve ON, closed, allowing a vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the purge valve OFF, closed, and the vent valve OFF, open, while monitoring the fuel tank pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inches H2O in a calibrated time, DTC P0446 will set.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0122, P0123, P0452, or P0453 are not set.
^ The ignition voltage is between 10-18 volts.
^ The barometric pressure (BARO) is more than 75 kPa.
^ The fuel level is between 15-85 percent.
^ The engine coolant temperature (ECT) is between 4-30°C (39-86°F).
^ The intake air temperature (IAT) is between 4-30°C (39-86°F).
^ The start-up ECT and IAT are within 9°C (16°F) of each other.
^ The vehicle speed sensor (VSS) is less than 121 km/h (75 mph).

CONDITIONS FOR SETTING THE DTC
^ The FTP is less than -10 inch H2O.
^ The condition is present for as long as 30 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the 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
The EVAP system tests run when the engine is first started and meets the Conditions for Running the DTC. An intermittent condition could be caused by a damaged EVAP vent housing, a temporary blockage at the EVAP vent valve inlet or a pinched vent hose. A blockage in the vent system will also cause a poor fuel fill problem.

Reviewing the Failure 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 1-10:

Steps 11-20:

The numbers below refer to the step numbers on the diagnostic table.
4. This step checks if the FTP sensor is functioning.
5. This step checks if the condition is present.
6. This step checks the EVAP vent valve electrical operation.
7. This step checks for a restricted EVAP vent valve
8. This step checks if the restriction is in the EVAP canister or the vent hose.