Evaporative Emission Control Canister: Description and Operation

EVAP Canister Control Valve:

Evaporative Emission Control Schematic:

The Evaporative Emissions System (EVAP) canister control valve is a spring-biased vacuum diaphragm valve, normally closed. When the engine is running, vacuum is applied to the valve and the valve is opened. Fuel vapors from the canister are now free to flow to the manifold when the purge port is uncovered by the throttle blade. When the engine is shut "OFF," no vacuum is applied to the valve, and the vapors are prevented from migrating to the intake manifold.