Evaporative Emissions System: Description and Operation

Evaporative Emission Control System (EVAP):

This system stores fuel vapor generated by the fuel tank in the canister when the engine is not running. The fuel vapor is stored in the canister until it is drawn into the combustion chamber and burned when the engine is started.
The components that make up the evaporative emission control system are the: air flow meter, charcoal canister, engine control unit, three-way check valve, vacuum switching valve, coolant temperature sensor, solenoid valves, intake air thermosensor, and throttle sensor.

CHARCOAL CANISTER

The charcoal canister stores gasoline vapors when the engine is not running.

ENGINE CONTROL UNIT

The engine control unit detects signals from input sensors and switches and controls the purge control solenoid valve.

THREE-WAY CHECK VALVE

The three way check valve controls fuel tank pressure.

VACUUM SWITCHING VALVE

The vacuum switching valve opens passage of vacuum line when vacuum is applied.

SOLENOID VALVES

The first solenoid valve (No. 1 purge control) opens and closes the vacuum passage to No. 1 purge control valve. The second control valve (No. 2 purge control) opens and closes the vacuum passage to the vacuum switch valve. Both solenoid vacuum valves are controlled by signals from the engine control unit.