Evaporative Emission Control System (EVAP) - General Information

The system collects fuel vapors that accumulate in the fuel system while the vehicle is parked and routes them to the intake manifold to be burned during normal engine operation.

Any EVAP system includes a special charcoal canister that collects fuel vapors. The method of venting vapors from the canister may vary depending on system design. The description below allows the reader to understand the operating principles of any type of EVAP system in detail.

The described design does not necessarily match the system installed on a specific vehicle. However, the operating principle is common to all models equipped with fuel injection. If any discrepancies are found, refer to the VECI label located under the hood.

The fuel filler cap is equipped with a two-way pressure/vacuum relief valve. In case of system failure, the valve vents fuel vapors to the atmosphere.

Another shut-off valve (ORVR valve) is installed near the fuel tank. It regulates venting of fuel vapors to the charcoal canister depending on pressure/vacuum changes caused by temperature changes.

On the way to the charcoal canister, fuel vapors pass through a two-way valve and through vent hoses into the charcoal canister installed in the engine compartment, where they are stored while the vehicle is parked.

When the engine is started and before it warms up to a specified temperature, the canister purge solenoid valve remains closed, allowing the diaphragm purge valve to open due to increased intake manifold vacuum. Fuel vapors are drawn from the canister through the diaphragm purge valve into the intake manifold, from where they enter the combustion chambers and are burned during normal engine operation.

The fuel tank is also equipped with a sensor that monitors pressure changes in the tank both while parked and while driving.