P0446

Circuit Description
The VCM monitors the performance of the EVAP system by applying a predetermined level of vacuum to the EVAP system and monitors the vacuum decay rate. The VCM sets this DTC if the vacuum decay rate is greater than a predetermined value. The VCM monitors the amount of vacuum and the amount of pressure in the EVAP system by monitoring the fuel tank pressure sensor. For this DTC, the VCM turns ON both the EVAP purge valve and the EVAP vent valve when the Conditions for Running the DTC are met. This applies an engine vacuum to a closed EVAP system. The VCM turns OFF both the EVAP purge valve and the EVAP vent valve when the system reaches a correct amount of vacuum. The EVAP system should quickly RELEASE the vacuum in the EVAP system with the EVAP purge valve OFF and the EVAP vent valve OFF, or open. This test indicates a blocked or restricted EVAP vent path if the EVAP system fails to release the vacuum quickly enough.

Conditions for Running the DTC
^ No active MAP sensor DTCs
^ No active TP sensor DTCs
^ No active VS sensor DTCs
^ No active O2 sensor DTCs
^ No active ECT sensor DTCs
^ No active IAT sensor DTCs
^ DTC P0125 not active
^ The fuel level is more that 12.5% but less than 87%
^ The system voltage is between 10 and 17 volts
^ The ECT is between 4°C and 30°C (39°F to 86°F)
^ The IAT is between 4°C and 30°C (39°F to 86°F)
^ The cold start temperature difference (ECT minus IAT) is less than 1.5°C when the IAT is more than the ECT or 8°C when the ECT is more than the IAT
^ The BARO is more than 72 kPa
^ The change in fuel tank vacuum is less than 0.6 in. of H2O, or the change in fuel level is less than 8%
^ The fuel tank vacuum level remains above a calibrated value for a specified number of seconds

Conditions for Setting the DTC
The VCM fails to detect a drop in the EVAP system vacuum over a calibrated number of seconds with the vent solenoid open.

Action Taken When the DTC Sets
^ The VCM illuminates the MIL during the first key cycle in which the DTC sets.
^ The VCM stores the conditions that were present when the DTC sets as a Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC
^ The Control Module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the Engine Coolant Temperature is more than 70°C (158°F) during the same ignition cycle).
^ Use the scan tool Clear Information function.

Diagnostic Aids

Important: An accurate indication of fuel level is required for the VCM to properly Pass or Fail this DTC. Always diagnose fuel level sensor DTCs before performing this DTCs diagnostic table. Always check for fuel level sensor DTCs stored in History.

Inspect the following conditions:
^ A loose, missing, damaged, incorrect or improperly installed fuel cap
^ Missing or damaged O-rings at EVAP canister fuel vapor and purge line fittings
^ A cracked or punctured EVAP canister
^ Incorrectly routed or damaged EVAP system purge and vapor lines
^ A damaged or disconnected EVAP purge line, vent hose or fuel tank vapor line
^ A stuck closed EVAP vent valve
^ A restricted or stuck closed fuel tank rollover valve
^ A poor connection at the VCM: Inspect the harness connectors for the following conditions:
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connection
^ A damaged harness: Inspect the wiring harness to the EVAP vent solenoid, EVAP purge solenoid and the fuel tank pressure sensor for an intermittent, open or short circuit
^ A kinked, pinched or plugged vacuum source, EVAP purge, or fuel tank vapor line. Verify that the lines are not restricted

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
The numbers below refer to the step numbers on the Diagnostic Table.
4. If the vacuum stored in the EVAP system is quickly released then an intermittent system restriction or failure of the EVAP vent valve or the EVAP fuel tank pressure sensor may have occurred.
5. Checking the vapor canister and the EVAP vent valve for restriction.
9. An EVAP pressure sensor that does not correctly respond to pressure, or vacuum, will cause this DTC to set. The EVAP pressure sensor monitors a range from 7.5 in. H2O of pressure to -17.5 in. H2O of pressure (vacuum). In order to test the EVAP pressure sensor for pressure response SEAL the system with the scan tool and use the EVAP pressure/purge diagnostic cart to apply pressure to the system. Compare the pressure gauge (in. H2O) on the diagnostic cart to the EVAP pressure sensor reading on the scan tool.