Enhanced EVAP System Operation

The EVAP control system collects the fuel vapors from the fuel tank. When the engine is not running, a canister filled with activated carbon (charcoal) stores the fuel vapors. When the engine is running, the stored fuel vapors are drawn from the canister, then mixed with the intake air flow, and consumed in the normal combustion process.

The Powertrain Control Module (PCM) uses the EVAP purge valve to control the flow of the fuel vapors from the canister. The PCM supplies the ground to energize the EVAP purge valve (purge ON). The PCM controls the ON and OFF time of the EVAP purge valve by a Pulse Width Modulated (PWM) signal. The PCM determines the EVAP purge valve PWM duty cycle based on certain operating conditions, such as mass air flow, engine coolant temperature, manifold absolute pressure, and intake air temperature.