1998 AUDI A4 diagram

24-40

Checking voltage supply

Test conditions

Fuse for injectors OK

Electrical Wiring Diagrams, Troubleshooting &
Component Locations

- Disconnect harness connector from fuel injector
to be tested.

- Connect diode test lamp (for measuring voltage) between Ground
(GND) and socket 1 of connector.
Pa
ge 47 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

24-41

- Switch ignition on. The diode test lamp should
light up.

- If diode test lamp does not light up, test for open
circuits in wiring between contact 1 and fuse for
injectors. If necessary, rectify open circuit.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
- If diode test lamp lights up, test activation of
injectors.

C - Testing activation of injectors

- Remove plug connector from the injector which
is to be tested.

Specified value: the diode test lamp should start flashing.
Note:
Diode test lamps with a low current draw continue to glow faintly between - Connect diode test lamp VAG 1527 between the battery positive
terminal (+) and contact 2 on the connector.
- Operate starter for a few seconds (the engine can be allowed to start).
Pa
ge 48 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
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

24-55

- 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
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

24-58

- 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

24-59

Mass Air FLow (MAF) sensor -G70,
checking


Requirements

Coolant temperature at least 80 C (175 F)

Electrical consumers switched off (radiator
fan must not run during test)
A/C switched off
Fuse for mass air flow sensor OK

Electrical Wiring Diagrams, Troubleshooting &
Component Locations

Checking function

- Connect vehicle diagnostic, testing and
information system VAS5051 or VAG1551 scan
tool and select engine electronics control
module by entering address word "01" Page
01
-9 . When doing this the engine must be at
idle.
Pa
ge 69 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

24-62

- Connect multimeter to terminal 2 of connector
and engine Ground (GND) for voltage
measurement.

- Operate starter briefly.

Specification: approx. battery voltage

Note:
Voltage is supplied to Mass Air Flow (MAF)
sensor from Fuel Pump (FP) relay.
If there is no battery voltage.

- Check wire connection from terminal 2 of
connector to Fuel Pump (FP) relay via fuse for
open circuit and short circuit to Ground (GND),
repair if necessary.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
Pa
ge 72 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