Activated Charcoal Filter System (Vehicles For Usa And Canada) - Volkswagen Touareg 2003 Workshop Repair Manual

Touareg 2003 ➤
8-cylinder injection engine - Edition 11.2011
4 Activated charcoal filter system (ve‐
hicles for USA and Canada)
Assembly overview - activated charcoal filter system
⇒ page 123 .
Checking fuel system for leaks
Function
Fuel vapour forms above the surface of the fuel in the fuel tank;
the quantity depends upon the air pressure and ambient temper‐
ature.
The activated charcoal filter system prevents these HC emissions
escaping to the atmosphere.
Fuel vapours pass from the highest point in the tank (on filler neck)
through the expansion tank and into the activated charcoal filter.
The activated charcoal stores these vapours like a sponge.
When the vehicle is being operated and the Lambda control is
active (engine warm), the activated charcoal filter system sole‐
noid valve 1 -N80- is activated (pulsed) by the engine control unit
-J623- depending on load and engine speed. The opening period
depends on the input signals.
During the purging procedure (regeneration of activated char‐
coal), the intake manifold vacuum draws fresh air through the vent
of the activated charcoal filter. The fuel vapours stored in the ac‐
tivated charcoal and fresh air are fed to combustion in metered
quantities.
The activated charcoal filter solenoid valve 1 -N80- is closed when
it is not supplied with current (e.g. open circuit). The activated
charcoal filter will not be purged.
Description of leakage diagnosis
The activated charcoal filter system, including fuel tank, is equip‐
ped with leakage diagnosis which can detect if there is a leak in
the system.
The diagnosis is based on a pressure method and indicates leaks
with a diameter greater than 0.5 mm.
During the diagnosis, the fuel system diagnostic pump -V144-
builds up pressure in the activated charcoal system. For this, the
activated charcoal filter solenoid valve 2 -N115- is closed. Once
the pressure is attained, the pump switches off. If the pressure
drops below a certain value, the pump switches on again. Self-
diagnosis monitors the intervals at which the pump is switched on
or off and if the intervals are too short, writes a fault to the fault
memory.
122
Rep. gr.20 - Fuel supply system
⇒ page 124 .