fuel pump AUDI A4 1999 B5 / 1.G EVAP Workshop Manual

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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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Checking voltage supply (all vehicles)

Note:
Voltage supply to the LDP is via the fuel pump
relay.

Test condition:

Fuse for LDP is OK

- Disconnect connector from LDP.

- Connect voltage tester VAG1527 B as follows:Connector terminal
Measure
3 Engine Ground (GND)
- Briefly operate starter motor.
LED must light up.
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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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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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If you did not find any malfunction, however the
Leak Detection Pump (LDP) did not function
during the Output Diagnostic Test Mode (DTM):

- Replace LDP Page 20
-162
If the LED does not blink, although wiring is OK:

- Replace the 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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Installing
Installation is in reverse order of removal, but do
the following:

Note:
Secure all hoses with clamps that are the same
as factory installed.

CAUTION!

Always refer to the latest parts catalog to
ensure that you use original equipment fuel
hose clamps.

Tightening torque: - Secure hose -2- with tie wrap -1- to bracket of LDP.Component
Nm
Bracket for Leak Detection Pump (LDP) 7.5
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If flow stops:

- Reconnect EVAP lines to search area that was
isolatedl
If leak or source of fuel odor cannot be found:

- Contact Audi Dealer Technician Helpline.

CAUTION!

Under no circumstances should the vehicle
be returned to the customer without proper
diagnosis and repair.
When leak has been located:

- Repair leak and repeat EVAP system test.

- Perform quality check and return vehicle to
customer.

Note:

Because leak may be at top of fuel tank, it may
not be possible to locate through fuel
pump/sending unit access plate.
Fuel tank may need to be lowered to locate the
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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-
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