AUDI A4 2000 B5 / 1.G EVAP Workshop Manual

20-130


EVAP system, servicing EVAP system components

1 -
Cap nut
10 Nm
2 -
Cover For EVAP canister
3 -
Stud 15 Nm
4 -
Sealing piece
5 -
Bleed line To EVAP canister purge regulator valve -
N80
6 -
Bleed line From gravity valve
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7 -
Vacuum hose
LDP / throttle actuator control module
Connection in engine compartment4 cylinder engine Fig. 16 cylinder engine Fig. 2
8 -
Cable tie
To mounting of vacuum line on LDP
bracket
9 -
Leak Detection Pump (LDP) -V144 Location: in left rear wheel house behind
wheel well Checking Page 20
-139
Removing and installing Page 20
-162
10 -
3-pin harness connector
Black
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11 -
Connecting hose
LDP / EVAP canisterPressure sideTo remove at LDP, press unlocking tab on
connector
12 -
10 Nm
13 -
Air filter For LDP
14 -
Sealing piece
15 -
Cable tie For mounting connecting hose on wheel
house
16 -
EVAP canister Location: lower front in spare wheel wellRemoving and installing Page 20
-164
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Vehicles with 1.8 ltr. turbo engine
The vacuum line for the LDP -V144 is connected to the Throttle actuator
control module line with a T-piece -arrow-. Fig. 1 Connections to LDP in engine compartment

Vehicles with 2.8 ltr. engine
The vacuum line from the LDP -V144 is connected to the EVAP canister
purge regulator valve with a T-piece -arrow-. Fig. 2 Connections to LDP in engine compartment
1 - to EVAP canister
2 - to LDP -V144
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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.
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If; however, the reed contact closes within 10
seconds, there is a leak. Then, the pump
continues to cycle for four more strokes. The
ECM measures the time for each of these four
strokes until the next time the reed contact
closes. In this fashion, the ECM can
differentiate between "fine" and "large" leaks.
Leak detection is automatically triggered,
shortly after each engine start. If there is an
incorrect measurement, a malfunction is stored
in DTC memory.
A warning will appear on the instrument panel if
the malfunction has occurred during two
successive drives. Also, leak detection can also
be activated using the VAG1551 Scan Tool
Page 20
-139
.
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Fuel tank and EVAP system, checking
for leaks


Note:
In the following, individual questionable points
will be considered that could be leaks in the fuel
tank and tank ventilation system. After
eliminating a possible leak, it is effective to then
perform a tank leak diagnosis to determine
whether the leak was successfully sealed.

- Switch OFF ignition.

- Check if filler cap was completely closed for the
test.

- Check if filler cap seal is damaged or crimped,
replace if necessary.

- Check if the gaskets under the cover flanges are
OK and if the union nut on the fuel tank cover
flange is correctly tightened.

- Check hose connections for tightness and
integrity repair or replace as necessary.

- Remove luggage compartment trim.
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- Remove connector flange cover under luggage
compartment trim.
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Note:
Observe the cover flange installation instructions.

Front wheel drive Page 20
-44


All wheel drive Page 20
-97
.

- Visually inspect all fuel tank system line and
hose connections and replace any leaking lines,
for example:


Line from EVAP canister to EVAP canister
purge regulator valve in engine
compartment.

Lines from EVAP canister to the LDP (under
left wheel house liner).

Line from the fuel tank to the EVAP canister
(under the cover for the EVAP canister).

Lines of the tank ventilation system (under
right wheel house liner).

Fuel lines to the engine.

Note:
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Locate leaks at lines and components of the tank
system by using a non-combustible,
environmentally friendly, leak detector spray.
Perform several leak diagnostics in a row to build
up the system pressure. Bubbles will form at
points of leakage.
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