Evaporative Emissions System: Description and Operation

EVAP System, Through 08.06

• Vehicles through 08.06 also have an Evaporative Emission (EVAP) canister purge solenoid valve 2 (N115) and a pressure retention valve --> [ (Item 20) Pressure retention valve ] EVAP System Assembly Overview, through 08.06.

Function

Depending on air pressure and ambient temperature, varying quantities of fuel vapors form above the fuel surface in the fuel tank.

The EVAP system prevents these Hydrocarbon (HC) emissions from entering the atmosphere.

Fuel vapors travel from the highest point of the fuel tank (at filler tube) via expansion tank into 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 EVAP canister purge regulator valve 1 (N80) is activated by the Engine Control Module (ECM) (J623) in pulses dependent on load and engine speed. The opening time is dependent on input signals.

During the cleansing process (regeneration of active charcoal), the intake manifold vacuum sucks fresh air through the breather connection of the EVAP canister. The fuel vapors stored amongst the activated charcoal and fresh air are proportionately supplied to be burned.

EVAP canister purge regulator valve 1 (N80) is closed without current (e.g. open circuit). The EVAP canister is not purged.

Leak Detection Function Description

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

The diagnosis operates by pressurizing the system and should detect leaks where the damage exceeds 0.5 mm in diameter.

During diagnosis, positive pressure is created in the EVAP system by the Leak Detection Pump (LDP) (V144). To do this, the EVAP canister purge solenoid valve 2 (N115) is closed. The pump will switch off when the pressure is attained. When the pressure falls to below a certain figure, the pump will switch on again. On Board Diagnostic (OBD) monitors the switch intervals and stores a Diagnostic Trouble Code (DTC) in DTC memory if the intervals are too short.

• Hose connections are secured with either spring type or clamp type clips.

• For installing spring type clips, the spring type clip pliers (VAS 6340)

• or the Space saving clip pliers (VAS 6362) are recommended.

Observe safety precautions. Refer to --> [ Safety Precautions ] Safety Precautions.

Observe rules for cleanliness. Refer to --> [ Clean Working Conditions ] Clean Working Conditions.