| Function of activated charcoal filter system |
| Fuel vapour forms above the surface of the fuel in the tank; the quantity depends upon the air pressure and ambient temperature. |
| The activated charcoal filter system prevents these HC emissions escaping to the atmosphere. |
| In limited quantities, fuel vapours pass from the highest point in the tank through the gravity valve (which closes at an angle of 45°) and through a pressure retention valve into the activated charcoal filter. |
| The activated charcoal stores these vapours like a sponge. |
| When the car is being driven and the Lambda control is active (engine warm), the activated charcoal filter solenoid valve 1 -N80-, also known as regeneration valve, is activated (pulsed) by the engine control unit depending upon load and engine speed. The opening period depends on the input signals. |
| During the purging procedure (regeneration of the activated charcoal), the intake manifold vacuum draws in fresh air through the breather opening on the underside of the activated charcoal canister. The fuel vapours stored in the activated charcoal and fresh air are fed to combustion in metered quantities. |
| The pressure retention valve prevents fuel vapours from being drawn from the fuel tank when the solenoid valve is open and intake manifold vacuum is present. It thus ensures that the purging of the activated charcoal filter has priority. |
| When not energised (e.g. open circuit), the solenoid valve is closed. The activated charcoal filter will not be purged. |
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