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, check and cut valve, engine control unit, ignition coil, fuel/vapor separator, purge control solenoid valve, three-way check valve, vacuum switching valve, coolant temperature sensor, and a thermo-vacuum valve.

CHARCOAL CANISTER

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

CHECK AND CUT VALVE

The check and cut valve releases excessive pressure or vacuum in the fuel system and vents it to/from the atmosphere.

ENGINE CONTROL UNIT

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

FUEL/VAPOR SEPARATOR

The fuel/vapor separator prevents liquid fuel from entering the charcoal canister.

PURGE CONTROL SOLENOID VALVE

The purge control solenoid valve is used to control the vacuum signal to the vacuum switch valve.

THREE WAY CHECK VALVE

The three way check valve controls pressure in the fuel tank.

VACUUM SWITCH VALVE

The vacuum switch valve regulates the flow of evaporative fumes from the charcoal canister to the intake manifold.

THERMO-VACUUM VALVE

The thermo-vacuum valve controls the vacuum applied to the No. 1 purge control valve and solenoid valve (Purge). The valve opens the vacuum passage at temperatures above 54°C (129°F).