Evaporative Emissions (EVAP) system: Function: Notes

Depending on air pressure and ambient temperature, fuel vapor will form above the level of fuel in the tank.

The EVAP system prevents these HC emissions from escaping into the atmosphere.

In limited quantities, fuel vapors located at the highest point in the tank pass through a gravity valve (which closes at an angle of 45 ° ) and through a pressure retention valve into the EVAP canister.

The activated charcoal in the canister stores these vapors like a sponge.

When the Oxygen sensor control is active when driving (engine warm), the EVAP canister purge regulator valve N80 (sometimes called regeneration valve), is activated (pulsed) from the engine control module depending upon load and engine speed. The opening period is dependent on the input signals.

Intake manifold vacuum draws fresh air through the vent opening on the underside of the EVAP canister during the purging procedure (regenerating the activated charcoal). The fuel vapors stored in the activated charcoal and fresh air are fed for combustion in dosed quantities.

The pressure retention valve prevents fuel vapors from being drawn from the tank when the solenoid valve is open and an intake manifold vacuum is present. It therefore ensures that the evacuation of the EVAP canister has priority.

When no voltage is applied (e.g. wiring open circuit), the solenoid valve is closed. The EVAP canister will not purge.

The vacuum pipe from the throttle valve control module to the EVAP canister has an additional by-pass which is connected with the crankcase breather valve. The non-return valve integrated in the crankcase breather valve prevents intake air entering into the crankcase during some partial load ranges. This improves the overall crankcase breathing. The by-pass guarantees the crankcase breathing.