fuse AUDI A4 1998 B5 / 1.G AEB Engine Motronic MFI And Ignition System

BEFORE cranking engine at starting RPM
(e.g. for compression testing) disable ignition
and fuel injection systems:

Disconnect both ignition coil power output
stages, and both Motronic fuses at the E-box
in the plenum.
Disconnect harness connectors from all fuel
injectors.
Afterward, erase DTC memory.
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24-27

Oxygen Sensor (O2S) heater (before
TWC), checking


Notes:

Harness connector for Oxygen Sensor (O2S)
heater: 4-pin, brown
Component locations Page 24
-1 .

Required special tools and test equipment

VAG 1551 or VAG 1552 Scan Tool (ST) with
VAG 1551/3 adapter cable
VAG 1598/22 test box
Multimeter US 1119 (Fluke 83 or equivalent)
VW 1594 connector test kit
Wiring diagram

Test requirements
Fuse for Oxygen Sensor (O2S) heater OK
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24-43

Oxygen Sensor (O2S) heater (behind
TWC), checking


Notes:

Harness connector for Oxygen Sensor (O2S)
heater: 4-pin, black
Component locations Page 24
-1

Required special tools and test equipment

VAG 1551 or VAG 1552 Scan Tool (ST) with
VAG 1551/3 adapter cable
VAG 1598/22 test box
Multimeter US 1119 (Fluke 83 or equivalent)
VW 1594 connector test kit
Wiring diagram

Test requirements
Fuse for Oxygen Sensor (O2S) heater OK
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24-57

Mass Air Flow (MAF) sensor, checking


Required special tools and test equipment

VAG 1551 or VAG 1552 Scan Tool (ST) with
VAG 1551/3 adapter cable
VAG 1598/22 test box
Multimeter US 1119 (Fluke 83 or equivalent)
VW 1594 connector test kit
Wiring diagram

Test requirements
All electrical consumers switched off (coolant
fan must not run during test).
A/C must be switched off
Fuse for MAF sensor OK
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24-79
Evaluation of display group 4 Display group: 4


Display field: 2
Possible cause
Corrective action
No VAG 1551 display
Fuse for ECM faulty- Replace fuse
Open circuit in wiring- Voltage supply at terminal 15 Page 24
-
80

Displayed value changes between 10.0-14.5
V
Intermittent connection - Voltage supply at terminal 30 Page 24
-
79

0.0-10.0 V
Battery
discharged/faulty Voltage regulator faulty - Check battery
- Check generator
- Check voltage regulator
14.5-16.5 V Generator faultyVoltage regulator faulty - Check generator
- Check voltage regulator

Checking voltage supply at terminal 30

- Switch ignition off.

- Connect VAG 1598/22 test box to ECM harness
connector Page 01
-56
.
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24-81

Fuel pump relay and connections,
checking


The fuel pump relay is located at relay position 4 on the relay panel on the
left side under the instrument panel.
Checking function of fuel pump relay -J17-
- Remove storage shelf in left-front footwell.

- Remove fuses 28, 29 and 34 from fuse panel.
- Connect VAG 1527B LED voltage tester between Ground and one of
the two terminals for fuse 28.
- Briefly crank starter.

LED test light must light up.
Fuel pump relay must be actuated (sound and vibration)
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24-82
If the fuel pump does not respond:

- Check power supply wiring Page 24
-84
.
If the LED test light does not light up:

- Repeat test at other terminal of fuse 28.

If the LED light still does not light up:
- Check wiring for open or short circuits between fuse 28 and terminal 30
at relay position 6, using the applicable wiring diagram. Repair wiring
as necessary.

Note:
This step lets the fuel pump run without the engine running. The closed
throttle position switch must be closed during the test, or the selected fuel
injector will discharge fuel when it is actuated 5 times. - Connect VAG 1527B LED voltage tester between Ground and one of
the two terminals for fuse 29.
-
Initiate output Diagnostic Test Mode (DTM) and advance to test of
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24-83
If the LED test light does not light up:

- Repeat test at other terminal of fuse 29.

If the LED test light does not light up:
- Check wiring for open circuit between fuse 29 and terminal 30 at relay
position 6, using the applicable wiring diagram. Repair wiring as
necessary.

Note:
This step lets the fuel pump run without the engine running. The closed
throttle position switch must be closed during the test, or the selected fuel
injector will discharge fuel when it is actuated 5 times. - Connect VAG1527 LED voltage tester between Ground and one of the
two terminals of fuse 34.
- Initiate output Diagnostic Test Mode (DTM) and advance to test of
cylinder 1 fuel injector -N30- Page 01
-42
.

LED test light must light up
Fuel pump relay must be activated
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24-84
If the LED test light does not light up:

- Repeat test at other terminal of fuse 34.

If the LED test light does not light up:
Checking fuel pump relay voltage supply
If voltage is NOT OK: - Check wiring for open circuit between fuse 34 and terminal 31 at relay
position 6, using the applicable wiring diagram. Repair wiring as
necessary.
- Remove fuel pump relay -J17- from relay panel position 6.
- Switch ignition on.
- Connect multimeter US 1119 (Fluke 83 or similar) and check for
voltage at relay socket:

Terminals 28 (B+) and 34
Terminals 32 (B+) and 34
Specified values: approx. Battery Positive Voltage (B+)
- Repair wiring according to applicable wiring diagram.
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24-85

Checking fuel pump relay signal

Fuel pump relay -J17- removed
Fuses 28, 29 and 34 removed from fuse
panel

If the LED test light does not light up while cranking the starter, check
wiring as follows. - Connect VAG 1527B LED voltage tester between relay socket
terminals 28 (B+) and 29.
LED test light must light up (dimly).
- Briefly crank starter; LED test light must continue to light up (dimly).

If resistance is NOT OK: - Connect VAG 1598/22 test box to ECM harness connector Page 01
-
56
. (Numbers marked on ECM connector match those on test box).
- Connect multimeter US 1119 (Fluke 83 or equivalent) to check for open
circuit between relay socket terminal 29 and test box socket 4.

Specified value: max. 1 - Repair wiring using applicable wiring diagram.
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pair&id=AUDI.B5.FU02.24.1