The EVAP vent valve controls evaporative emissions by storing fuel vapor and purging the vapor into the engine at specific times. The EVAP vent valve is closed when the engine is OFF, and opens during start up to purge the vapor so it can be burned during the combustion cycle. The ECM monitors fuel tank pressure during normal operation and opens the valve periodically to relieve pressure and evacuate fuel vapor. When activated the evaporative canister purge valve allows the fuel vapor to flow from the EVAP canister to the engine. The normally closed evaporative canister purge valve is pulse width modulated by the Engine Management System in order to control the vapor flow.
The following symptoms can be caused by a faulty EVAP vent valve.