Circuit Description

The DTC P0449 Evaporative Emission (EVAP) Vent System Performance diagnostic monitors the control circuit voltage of the EVAP vent valve. Ignition voltage is supplied directly to the EVAP vent valve solenoid. The Powertrain Control Module (PCM) supplies a ground path to the solenoid control circuit using an internal solid state device called a driver. Each driver has a fault line that is monitored by the PCM. When the PCM commands the solenoid ON, the voltage on the control circuit should be about zero or low. When the PCM commands the solenoid OFF, the voltage on the control circuit should be about battery voltage or high. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

The PCM will monitor the solenoid control circuit for the following conditions:

• A short to ground.
• A short to voltage.
• An open circuit.
• An open solenoid.
• An internally shorted or excessively low resistance solenoid coil.