Function Description of Evaporative Emissions (EVAP) System

Function Description Of Evaporative Emissions (EVAP) System

Depending upon air pressure and ambient temperature - more or less fuel vapors will form in the fuel tank.

The EVAP canister system prevents these HC emissions from entering the atmosphere.

With quantity restrictions, fuel vapors travel from the highest point of the fuel tank via the gravity valve (closed at a tilt of 45 degrees) and the pressure retention valve to the EVAP canister.

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

While driving, with oxygen sensor control active (engine warm), the Evaporative Emission (EVAP) Canister Purge Regulator Valve N80, (also called the regeneration valve) is activated by the Engine Control Module (ECM) in pulses dependent on load and engine speed. The open duration is dependent on the input signals.

When purging (recovery of the activated charcoal), the suction tube vacuum sucks fresh air in through the ventilation opening on the underside of the EVAP canister. The fuel vapors stored amongst the activated charcoal and fresh air are proportionately supplied to be burned.

The pressure retention valve prevents fuel vapors from being sucked out of the tank when the Evaporative Emission (EVAP) canister purge regulator valve is opened 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 is not purged.

Function description of leak diagnosis (only with engine codes AHA, ATQ)

The EVAP system (including fuel tank) is equipped with leak diagnosis. The leak diagnosis will detect whether the system is leaking (insufficient sealing).

The diagnosis operates by pressurizing the system and should detect leaks where the damage exceeds 1 mm in diameter.

During the diagnostic, the Leak Detection Pump (LDP) V144 generates a positive pressure of approx. 30 mbar in the EVAP canister system. The pump will switch off when the pressure is attained once. When the pressure falls to below a certain figure, the pump will switch on again. On Board Diagnostic monitors the switch intervals and stores a DTC in DTC memory if the intervals are too short.