EVAP Control

The PCM controls the [1][2]EVAP solenoid using a pulse width modulated (PWM) signal. By using this type of control, the PCM can vary the rate (duty cycle) at which it opens or closes the solenoid. As mentioned, a strict set of conditions must be met before the PCM will enable canister purge. This optimizes driveability and evaporative emission reduction.

Once the PCM decides to enable the [1][2]EVAP solenoid, it monitors rear oxygen sensor data to determine if the air/fuel mixture is correct. If the PCM determines the air/fuel mixture is incorrect, it will adjust the EVAP solenoid duty cycle to provide the correct amount of fuel vapor from the EVAP canister. This process is called duty cycle learning.