1998 AUDI A4 fuel pump

24-48

Checking for leaks

- Bridge sockets 1 and 65 on the test box using
test leads from VAG1594 A connector test kit.
(This creates an Ground (GND) connection to
one side of the fuel pump relay coil.)

Note:
Once the socket are bridged the fuel pump runs
continuously, even if the engine is not running.
This is because the fuel pump relay receives its
positive voltage supply via the central electrics.
The negative voltage supply for the fuel pump
relay comes via the cable bridge on the test box.

WARNING!

Fire hazard. DO NOT smoke or work near
heaters or have anything in the area that can
ignite fuel!

- Check injectors fuel for leaks (visual check).
When fuel pump is running, only 1 or 2 drops
should escape per minute from each injector.

- If fuel loss is greater, switch off fuel pump
(remove bridge) and replace faulty injector
Page 24
-53
, also observe notes on Page 24
-
53
.
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ge 57 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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e=re
pair&id=AUDI.B5.FU04.24.1

24-49


WARNING!
Make sure test box is inside of passenger compartment.
The fuel pump should run. - Connect one fuel injector terminal to engine Ground (GND) using test
cable and crocodile clamp from VAG1594 connector test kit.
- Connect second fuel injector terminal to B+ using remote control
VAG1348/3 A, adapter cable VAG1348/3-2 and auxiliary cable.
- Bridge sockets 1 and 65 on the test box using test leads from
VAG1594 A connector test kit. (This creates an Ground (GND)
connection to one side of the fuel pump relay coil.)
Pa
ge 59 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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pair&id=AUDI.B5.FU04.24.1

24-50

- Activate remote control VAG1348/3 A for 30
seconds.

- When all three fuel injectors from the first bank
of cylinders have been activated, place the three
measuring glasses on a level surface.

Specified value for each fuel injector: 135 ... 165
ml

- If measured value for one or more of fuel
injectors is outside tolerance range, switch off
fuel pump (switch ignition off) and replace faulty
fuel injector Page 24
-53
, also observe notes
on Page 24
-53
.
Pa
ge 60 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-54

Fuel Pump (FP) relay -J17 and relay
activation, checking


Note:

The fuel pump relay is located in the central electrics in the left-hand
footwell, relay position 4.
A - Checking Fuel Pump (FP) relay -J17
- Remove storage bin in front left-hand footwell.

Electrical Wiring Diagrams, Troubleshooting & Component Locations
The fuel pump relay should pick up (can be felt and heard) and the diode
test lamp should light up. - Remove fuel pump fuse from fuse holder and connect diode test lamp
VAG1527 between Ground and one of the two contacts for the fuel
pump fuse. - Operate starter briefly.
- If fuel pump relay does not pick up, check activation Page 24
-56
.
Pa
ge 64 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-55

- If fuel pump relay picks up but diode test lamp
does not light up, repeat test on other terminal.

Electrical Wiring Diagrams, Troubleshooting & Component Locations - If diode test lamp still does not light up, test for open circuit in wiring
between fuel pump fuse and terminal 23 in relay position 4. If
necessary, rectify open circuit. - If voltage supply, activation and wiring for fuel pump relay are OK,
install new fuel pump relay.
Pa
ge 65 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1

24-56

B - Checking voltage supply and activation of
fuel pump relay

Note:
Activation of the fuel pump relay can also be
tested using the final control diagnosis Page
01
-75
.

- Remove fuel pump relay -J17 from central
electrics, relay position 4.

Checking voltage supply

- Switch ignition on.

Specification: approx. battery voltage in each case
Electrical Wiring Diagrams, Troubleshooting & Component Locations - Connect hand-held multimeter VAG1526 between Ground (GND) and
relay panel contact 19 (B+; terminal 15 from ignition switch).
Disconnect, then re-connect between Ground (GND) and relay panel
contact 17 (permanent B+; terminal 30 from battery).
- If values are not as specified, rectify open circuit.
Pa
ge 66 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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e=re
pair&id=AUDI.B5.FU04.24.1

24-57

Checking activation

Note:
Diode test lamps with a low current draw do not go out completely but
continue to glow faintly until the starter is operated.
If the diode test lamp does not light up, test the wiring as follows: - Connect diode test lamp VAG1527 between B+ and contact 16 on
relay panel (Ground connection via engine control module).
- Operate starter briefly.
- The diode test lamp should light up and remain lit when the starter is
operated.
- If activation, wiring and power supply for fuel pump relay are OK but
fuel pump relay still does not pick up, replace fuel pump relay.
- Connect VAG1598/31 test box to wiring harness for engine control
module. Do not connect to the engine control module itself Page 24
-
20
.
Pa
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port Fuel In
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(MFI
) system, servicin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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e=re
pair&id=AUDI.B5.FU04.24.1

24-58

- Connect hand-held multimeter between contact
16 on relay panel and socket 65 on the test box,
then test wiring for open circuits.

- Rectify open circuit if necessary.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
- If there is no open circuit and the diode test lamp
still does not light up:

- Replace Engine Control Module (ECM) Page
24
-24
.

- Reinstall fuel pump fuse.
Pa
ge 68 of 90 Motronic Multi
port Fuel In
jection
(MFI
) system, servicin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.1