1996 AUDI A4 AWM Engine Additional Signals Checking Workshop Manual

24-163


Additional signals, checking Special Tools and Equipment

VAG1526A
VAG1527B
VAG1594A
VAG1598/31
VAS5051 with VAG5051/1
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Engine speed signal, checking


Note:
The engine speed signal is output at terminal 37
of the Engine Control Module (ECM). The signal
is used, among other things, for RPM display in
the instrument cluster.

- Connect VAG1598/31 test box at wiring harness
to Engine Control Module (ECM), do not connect
ECM Page 24
-19
.

- Check the following wire connection for open
circuit and short circuit to Ground (GND) and B+:

Test box
VAG1598/31
Socket
Instrument cluster

Terminal
37 Electrical Wiring Diagrams,
Troubleshooting & Component
Locations

- Repair open circuit or short circuit if
necessary.
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Vehicle speed signal, checking


Notes:

The vehicle speed signal is generated by the
speedometer Vehicle Speed Sensor (VSS) -
G22- (at transmission) and is processed in the
instrument cluster.
The processed signal enters at terminal 54 of
the ECM and is used for idle stabilization and
tip-in shock reduction during shifting.

Test requirement:
Function and display of speedometer OK.
Troubleshooting:

Repair Manual, Electrical Equipment, Repair
Group 90; Instrument cluster; Speed signal, checking


Test sequence

WARNING!

To reduce the risk of accident during road
tests, always observe safety precautions
Page 24
-1 .
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- Connect VAS5051 tester Page 01
-7 and
select vehicle system "01 - Engine electronics".
Engine must run at idle for this.
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Display on VAS5051:
- Select diagnostic function "08 - Read Measuring Value Block" in
selection -1-.

Display on VAS5051:
1 - Enter display group Max. input value = 255
- Select function "005" in button field -2- for "display group number 005"
and press Q button to confirm input.
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Display on VAS5051:
- Determining via road test whether vehicle speed is displayed in display
field -3-.
- If vehicle speed is not display, lift vehicle -if possible using a vehicle lift-
until front left wheel is free.
- Connect VAG1598/31 test box at wiring harness to Engine Control
Module (ECM), do not connect ECM Page 24
-19
.
- Connect VAG1527B voltage tester to sockets 3 (B+) and 54 (VSS) of
VAG1598/31 test box.
- Switch ignition on and turn front left wheel by hand.

LED must blink (very brief blink signal).
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If LED does not blink:

- Check the following wire connection for open
circuit and short circuit to Ground (GND) and B+:

Test box
VAG1598/31
Socket
Instrument cluster

Terminal
54 Electrical Wiring Diagrams,
Troubleshooting & Component
Locations

- Repair open circuit or short circuit if
necessary.
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A/C compressor shut-off, checking


Notes:

The A/C compressor signal communicates to
the ECM that the compressor will be switched
on in 140 ms.
The Engine Control Module (ECM) can switch
off the A/C compressor via the same wire
connection.
Engine Control Module (ECM) switches off A/C
compressor:

-- during hard acceleration (Wide Open
Throttle 1st gear)

-- in emergency mode (emergency
operation)

-- after initiating basic setting (function 04)
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