Evaporative Emissions System: Description and Operation

PURPOSE
The evaporative emission control system (EVAP) prevents fuel vapors generated in the fuel tank from escaping into the atmosphere.

OPERATION
Fuel vapors from the fuel tank flow through the fuel tank pressure control valve and vapor pipe/hose to be stored temporarily in the EVAP canister. When the vehicle is in operation, fuel vapors stored in the EVAP canister flow through the EVAP purge solenoid and purge port and go into the intake manifold plenum to be sent to the combustion chamber.

When the engine coolant temperature is low or when the intake air quantity is small (when the engine is at idle, for example), the engine control module brings the EVAP purge solenoid into the OFF state to shut off the fuel vapor flow to the intake manifold plenum. This not only insures the driveability when the engine is cold or running under low load but also stabilizes the emission level.