Evaporative emissions (EVAP) system: Function

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

The evaporative emissions system prevents these HC-emissions from dispersing into the environment.

Fuel vapors disperse from the highest point of the fuel tank (at the filler neck) through the gravity valve (which closes at an inclination by 45 ° ) into the EVAP canister.

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

When driving with active Oxygen sensor regulation (engine warm), the evaporative emission (EVAP) canister purge regulator valve N80 is activated based on load and speed. The open duration is dependent on the input signals.

Without electricity (e.g. open circuit) the evaporative emission (EVAP) canister purge regulator valve remains closed. The EVAP canister is not purged.

Function description of leak diagnosis  

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 1 mm in diameter.

Before every leak diagnosis the Evaporative Emission (EVAP) Canister Purge Solenoid Valve 2 N115 is briefly opened to relieve any possible pressure.

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

• The spring-type clip pliers VAS 5024A are recommended for installing spring-type clips.

Observe safety precautions, refer to Safety precautions when working on fuel supply system  .

Observe rules for cleanliness, refer to Rules for cleanliness  .