1998 AUDI A4 ignition

24-183

- Take vehicle for a test drive and check whether
vehicle speed appears in display field 3.

- If vehicle speed does not appear, raise the
vehicle (preferably using a lift) until front left
wheel is clear of the ground.

Electrical Wiring Diagrams, Troubleshooting & Component Locations - Connect VAG1598/31 test box to wiring harness for engine control
module. Do not connect to the engine control module itself Page 24
-
20
.
- Connect diode test lamp between socket 3 (B+) and socket 54 (vehicle
speed signal).
- Switch ignition on and turn front left wheel by hand.
The diode test lamp should flash (very brief flashes).
- If diode test lamp does not flash, check for open circuit or short to B+
or Ground (GND) in wiring between instrument panel and terminal 54
on engine control module connector.
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24-185

Brake light switch -F and brake pedal
switch -F47, checking


- Connect vehicle diagnostic, testing and
information system VAS 5051 or VAG1551 scan
tool and select engine electronics control
module by entering address word "01" Page
01
-9 .
When doing this the ignition must be switched
on. Rapid data transfer
HELP
Select function XX

Indicated on display
- Press buttons -0- and -8- to select function "Read Measuring Value
Block" and confirm entry with -Q- button.
Read Measurin
g Value Block
Input displa
y group number XXX

Indicated on display
- Press buttons -0-, -6- and -6- to select "display group number 066" and
confirm entry with -Q- button.
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24-189
If specifications are not met:

Check voltage supply

- Connect VAG1527 B between following sockets
on harness connector:

Harness connector
terminal
Measure
against
1 Ground (GND)


The LED must come on
Harness connector
terminal
Measure
against
3 Ground (GND)

- Switch ignition on.


The LED must come on
If LED does not come on:

- Check wiring connection from terminal 1 or 3 of
connector for open circuit (fuse) or short circuit
to Ground (GND).
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24-191

Clutch Vacuum Vent Valve Switch -F36,
checking


Note:
This signal is used to avoid RPM over-oscillation
and load change impacts when changing gears
and is also used for the cruise control system.

Test sequence

- Connect vehicle diagnostic, testing and
information system VAS 5051 or VAG1551 scan
tool and select engine electronics control
module by entering address word "01" Page
01
-9 .
When doing this the ignition must be switched
on. Rapid data transfer
HELP
Select function XX

Indicated on display
- Press buttons -0- and -8- to select function "Read Measuring Value
Block" and confirm entry with -Q- button.
Read Measurin
g Value Block
Input displa
y group number XXX

Indicated on display
- Press buttons -0-, -6- and -6- to select "display group number 066" and
confirm entry with -Q- button.
Read Measuring Value Block 66

Indicated on display
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24-194
If specification is obtained:

Check voltage supply

- Connect VAG1527 B between following sockets
on harness connector:

Harness connector
terminal
Measure
against
2 Ground (GND)

- Switch ignition on.


The LED must come on
If LED does not come on:

- Check wire connection from terminal 2 of
connector for open circuit (fuse) or short circuit
to Ground (GND).

Electrical Wiring Diagrams, Troubleshooting &
Component Locations

- If necessary eliminate open circuit or short
circuit to Ground (GND)
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24-202

Checking bus system
The principle of the test is independent of the
number of control modules/systems connected to
the CAN-bus.
The DTC table suggested checking the data
exchange between the Engine Control Module
(ECM) and CAN capable control modules.

- Start engine (if engine will not start, switch
ignition on).

- Connect VAS5051 tester or VAG1551 scan tool
and select the control module for engine
electronics using "address word" 01 Page 01
-
9 .
Rapid data transfer
HELP
Select function XX

When indicated on display:
- Press buttons -0- and -8- to select "Read Measuring Value Block" and
press -Q- button to confirm input.
Read measurin
g value block
Q
Enter displa
y group number XXX

When indicated on display:
- Press buttons -1-, -2- and -5- to select "display group number 125" and
press -Q- button to confirm input.
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24-207


Example 1
From the malfunctions present in the DTC memories, you can see that
control module 1 has no connection to control modules 2 or 3.
Electrical Wiring Diagrams, Troubleshooting & Component Locations Control module
Stored malfunctions in DTC memory:
1
No message from control module 2No message from control module 3
2 No message from control module 1
3 No message from control module 1
- Switch ignition off.
- Disconnect control modules that are linked by bus wires and check
whether there is an open circuit in one of the bus wires - If no malfunction can be identified in the bus wires replace control
module 1.
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24-208


Example 2
From the malfunctions present in the DTC memories, you can see that
control module 2 has no connection to control modules 1 or 3.
Electrical Wiring Diagrams, Troubleshooting & Component Locations Control module
Stored malfunctions in DTC memory:
1
No message from control module 2
2 No message from control module 1No message from control module 3
3 No message from control module 2
- Switch ignition off.
- Disconnect control modules that are linked by bus wires and check
whether there is an open circuit in one of the bus wires - If no malfunction can be identified in the bus wires replace control
module 2.
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