tire pressure AUDI A4 1998 B5 / 1.G EVAP Workshop Manual

20-134

EVAP system leak detection


Function of leak detection system
The leak detection system can recognize leaks in
the entire fuel system, including the main fuel
tank, the EVAP canister and EVAP canister
purge regulator valve -N80.
On the mechanical side, the leak detection
system consists of a vacuum-operated
diaphragm pump (LDP) with a reed contact on
the pump diaphragm rod. The pump receives
vacuum from the intake manifold.

If the leak detection system is triggered; the
diaphragm pump pressurizes the fuel system
between 20 and 30 mbar.
If specified pressure is reached, the pump
diaphragm remains extended and the reed
contact remains in the "open" position.
If the pressure drops (i.e. there is a leak), the
diaphragm moves back and the reed contact
closes.
During diagnosis, first there is a measurement
of whether the reed contact has closed within
10 seconds. If this does NOT occur, the tank
system is then sealed.
Pa
ge 5 of 65 EVAP s
ystem, servicin
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11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE04.20.5

20-181


4 -
Bleed line
To gravity valve on fuel tank
5 -
EVAP canister Location: in bottom of spare tire well
6 -
Connecting hose LDP / EVAP canisterPressure side
7 -
Air filter For LDP
8 -
LDP -V144 Location: in left rear wheel house behind
wheel well Page 20
-130

9 -
Vacuum hose
LDP / throttle actuator control module
10 -
T - piece Location Fig. 1
Pa
ge 61 of 65 EVAP s
ystem, servicin
g
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE04.20.5

20-184


5 -
Vent valve
To gravity valve at fuel tank
6 -
Evaporative Emission (EVAP) canister Location: At bottom of spare tire well
7 -
Connecting hose Leak Detection Pump (LDP) /EVAP
canister Pressure side
8 -
Air cleaner For Leak Detection Pump (LDP) -V144-
9 -
Leak Detection Pump (LDP) -V144- Location: In left rear wheel well under
wheel well liner Removing and installing Page 20
-162
10 -
Vacuum line
To Leak Detection Pump (LDP) -V144-
Pa
ge 64 of 65 EVAP s
ystem, servicin
g
11/18/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.GE04.20.5