Evaporative Emission (EVAP) Control System Refer to the System Diagram to see the functional layout of the system. EVAP Canister The EVAP canister temporarily stores fuel vapour from the fuel tank until it can be purged back into the engine and burned (refer to the System Diagram to see the functional layout of the system). EVAP Canister Purge Valve When the engine coolant temperature is below 70°C (158°F), the ECM/PCM turns off the EVAP canister purge valve which cuts vacuum to the EVAP canister.