P0446

Circuit Description
The PCM monitors the performance of the EVAP system by applying a predetermined level of vacuum to the EVAP system then monitors the vacuum decay rate. The PCM sets this DTC if the vacuum decay rate is greater than a predetermined value.

Conditions for Running the DTC
^ DTCs P0107, P0108, P0112, P0113, P0121, P0122, P0123, P0131-P0161, P0420, P0430, P0500, P0502, P0503, P0562, P0563, P1111, P1112, not set.
^ The ignition voltage is between 10 and 18 volts. The barometric pressure is more than 75 kPa.
^ The fuel level is between 15% and 85% of full capacity.
^ The engine coolant temperature is between 4°C (39°F) and 30°C (86°F).
^ The intake air temperature is between 4°C (39°F) and 30°C (86°F).
^ The start up engine coolant temperature and the intake air temperature are within 9°C (16°F) of each other.

Conditions for Setting the DTC
^ The EVAP vacuum decay rate is greater than a predetermined value.
^ The conditions are present for greater than 2 seconds.

OR

^ The vacuum present in the EVAP system is greater than a predetermined value.
^ The conditions are present for greater than 4 seconds.

Important: This DTC does not report a first failed test. A first fail of this DTC will have a scan tool status as Not Run.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure records.

Conditions for Clearing the MIL/DTC
^ The PCM turns the MIL OFF after three consecutive ignition cycles that the diagnostic runs and does not fail.
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important:
^ Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
^ An accurate indication of fuel level is required for the PCM to properly Pass or Fail this DTC. Always diagnose fuel level sensor DTC's before performing this DTC's diagnostic table. Always inspect for fuel level sensor DTC's stored as History.
^ The Service Bay Test may have to be performed in cold ambient air temperatures when the vehicle is running a winter grade fuel. The scan tool displays a message when the service bay test does not run.
^ Inspect for charcoal release from the vapor canister.

Conditions for Running the Service Bay Test
^ The battery voltage is between 10.5 and 17.5 volts.
^ The fuel level is between 15% and 85% of the full capacity.
^ The engine temperature is between 3.5°C (38°F) and 35°C (95°F).
Perform a physical inspection of the EVAP system. Inspect for the following conditions:
^ A loose, missing, defective, or incorrect fuel tank cap
^ Incorrectly routed or defective EVAP system vacuum and vapor lines
^ A malfunctioning or damaged vapor canister
^ Inspect for charcoal release from the vapor canister.
The vacuum and pressure in the EVAP system is measured in inches of H2O (water). Most gauges measure vacuum in inches of Hg (mercury) and pressure in psi (pounds per square inch). The table illustrates how the values compare:

Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
2. An open in the Fuel Tank Pressure sensor ground circuit causes the voltage to go high. An open ground circuit may cause DTC P0446 to set, because the PCM senses a fuel tank pressure sensor voltage that is stuck in range, which indicates a restricted EVAP system. Refer to DTC P0453 for further diagnosis. P0453
An intermittent leak or restriction is indicated if the vehicle passes the Service Bay Test.
If the Service Bay Test can not be run, proceed to Step 5. If a fault is not currently present the diagnostic table steps will return you to Step 3.
4. An intermittent leak or restriction is indicated if the vehicle passes the Service Bay Test. A fuel tank cap that is loose or off causes this DTC to set.
If the Service Bay Test can not be run, proceed to Step 5. If a fault is not currently present the diagnostic table steps will return you to Step 3.
5. Testing the vapor canister and the EVAP Vent Valve for restriction.
9. A Fuel Tank Pressure sensor that does not correctly respond to pressure (or vacuum) causes this DTC to set.
The Fuel Tank Pressure sensor range is from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum).
In order to test the Fuel Tank Pressure sensor for vacuum response, command the EVAP Purge Solenoid Valve ON with the engine running and quickly SEAL the system using the scan tool. Leaving the EVAP Purge Solenoid Valve ON for a longer period of time allows a greater level of vacuum to develop.