Touareg V8-4.2L (AXQ) (2006)
Evaporative Emission Control Canister: Description and Operation
EVAP System
EVAP System
Function
Depending on air pressure and ambient temperature, varying quantities of fuel vapors form above the fuel surface in fuel tank.
The EVAP system prevents these HC emissions from entering atmosphere.
Fuel vapors travel from 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 Evaporative Emission (EVAP) Canister Purge Regulator Valve (N80) is activated
by Engine Control Module (ECM) (J623) in pulses dependent on load and engine speed. The opening time is dependent on input signals.
During cleansing process (regeneration of active charcoal), the intake manifold vacuum sucks fresh air through breather connection of EVAP canister.
The fuel vapors stored amongst the activated charcoal and fresh air are proportionately supplied to be burned.
Evaporative Emission (EVAP) Canister Purge Regulator Valve (N80) is closed without current (e.g. open circuit). 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 damage exceeds 0.5 mm in diameter.
During diagnosis, positive pressure is created in the EVAP system by Leak Detection Pump (LDP) (V144). To do this, the Evaporative Emission
(EVAP) Canister Purge Solenoid Valve 2 (N115) is closed. 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 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.