1999 AUDI A4 Ignition

20-136

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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20-138

- Visually inspect the fuel supply system
components:


Fuel tank

EVAP canister

LDP

EVAP canister purge regulator valve -N80

Note:
At times, the above components cannot be
effectively leak tested using a leak detection
spray, either because of component location or
function. In such cases, clamp off the lines to the
component involved and perform a leak check. If
the leak is no longer displayed, the clamped off
component is faulty. If the LDP is clamped off
and there is still a leak displayed, the LDP is
faulty.

- Check EVAP canister purge regulator valve -
N80

Repair Manual, Fuel Injection & Ignition,
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20-141


Note:
In the following description the performance of the On Board Diagnostic
(OBD) procedure the VAG1551 Scan Tool (ST) is used. When using
Vehicle Diagnostics Test and Information System VAS5051, use the
operating instructions. - Connect VAS5051 with diagnostic cable VAS5051/1 or VAG1551 Scan
Tool (ST) with adapter cable VAG1551/3B.
- Start engine and let idle.
On Board Dia
gnostic
HELP
1 - Rapid data transfer 1
)
2 - Blink code 1
)

Indicated on display: 1) Appears alternately
- Switch ignition on.
- Press button 1 to select "Rapid data transfer".
Rapid data transfer
HELP
Enter address word XX

Display will appear as shown
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20-146

Checking LDP via output DTM (vehicles with
electronic throttle control)

Note:
In the following description the performance of the On Board Diagnostic
(OBD) procedure the VAG1551 Scan Tool (ST) is used. When using
Vehicle Diagnostics Test and Information System VAS5051, use the
operating instructions. - Connect VAS5051 with diagnostic cable VAS5051/1 or VAG1551 Scan
Tool (ST) with adapter cable VAG1551/3B.
On Board Dia
gnostic
HELP
1 - Rapid data transfer 1
)
2 - Blink code 1)

Indicated on display: 1) Appears alternately
- Switch ignition on.
- Press button 1 to select "Rapid data transfer".
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20-148
If LDP -V144 is not activated (pump is silent):

- Switch ignition off.

- Remove LDP ( Page 20
-162
) and disconnect
electrical connector.
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20-152
If LED does not light up:

Electrical Wiring Diagrams, Troubleshooting & Component Locations
If wiring is OK:
Repair Manual, Fuel Injection & Ignition, Repair Group 24 - Check electrical wiring from terminal 3 via fuse for fuel pump relay for
open circuit. - Repair wiring as necessary.
- Check fuel pump relay:
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20-153

Checking output wiring (vehicles with
mechanical throttle activator)

- Remove weatherstrip at plenum chamber -arrows-.
- Remove cover for plenum chamber -1- toward front.
- Remove cover for E-box in plenum chamber.

Note:
Disconnect or connect the Engine Control Module (ECM) connector only
with ignition switched off. - Carefully lever off clamp -arrow- with screwdriver.
- Unlatch clip and disconnect connector for Engine Control Module
(ECM).
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20-155
If you did not find any malfunction, however the
Leak Detection Pump (LDP) did not function
during the output Diagnostic Test Mode (DTM):

- Replace Leak Detection Pump (LDP) -V144
Page 20
-162
.
If the LED does not blink, although wiring is OK:

- Replace Engine Control Module (ECM):

Repair Manual, Fuel Injection & Ignition,
Repair Group 24
- Generate readiness code:

Repair Manual, Fuel Injection & Ignition,
Repair Group 24
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