P0446

The EVAP Vent valve is supplied power via the Engine Controls Power Relay (Switched B+). The Engine Control Module (ECM) controls the valve by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the ECM. When the ECM is commanding a component on, the voltage of the control circuit should be low (near 0 volts). When the ECM is commanding the control circuit to a component off, the voltage potential of the circuit should be high (near battery voltage).

If the fault detection circuit senses a voltage other than what is expected, this DTC will set.
The ECM will monitor the EVAP Vent valve circuit for the following:
^ A short to ground
^ A short to voltage
^ An open circuit
^ An internally shorted or excessively low resistance EVAP Vent valve circuit

When the ECM detects any of the above malfunctions, this DTC will set and the affected driver will be disabled. The ECM will continue to test the circuit and if the fault goes away, the driver will be reactivated.

Conditions for Running the DTC
^ The ignition voltage is between 7.5 volts and 15.0 volts.
^ The engine speed is greater than 40 RPM.

Conditions for Setting the DTC
A short to ground, an open circuit, or a short to battery voltage is detected on the control circuit.

Action Taken When the DTC Sets
The ECM illuminates the Malfunction Indicator Lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.

Conditions for Clearing the MIL/DTC
^ The ECM turns off the MIL after three consecutive drive trips that the diagnostic runs and passes.
^ A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic.
^ The ECM battery voltage is interrupted.
^ The scan tool clears the MIL/DTC.

Diagnostic Aids

Notice: Refer to J 35616-A Connector Test Adapter Kit Notice in Service Precautions.

^ Use the Connector Test Adapter Kit J 35616-A for any test that requires probing the ECM harness connector or a component harness connector.
^ If an intermittent circuit problem is suspected, check for a damaged harness. Inspect the wiring harness thoroughly. If the harness appears to be OK, observe the scan tool while moving the related connectors and the wiring harnesses. A change in the display may help locate the fault.

Refer to Symptoms for the Intermittents. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table:
2. Listen for an audible click when the valve operates. Repeat the commands as necessary.
3. This check can detect a partially shorted coil which would cause excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm the coil may open (amps drop to 0), or short (goes above 0.75 amp).
18. If no trouble is found in the control circuit or the connection at the ECM, the ECM may be damaged, however, this is an extremely unlikely failure.