1997 AUDI A4 APB Engine Additional Signals Checking Workshop Manual

24-179


Additional signals, checking

Engine speed (RPM) signal, checking


Note:
The engine speed signal is taken from terminal
37 on the Engine Control Module (ECM). The
signal is used for various functions including the
RPM display in the instrument cluster.

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
.
- Check wiring from test box socket 37 to instrument cluster according to
wiring diagram for an open circuit.
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24-180

Fuel consumption signal for on-board
computer, checking


Notes:

The fuel consumption signal is calculated by the
engine control module (on the basis of the
injection period) and passed on to the on-board
computer. The fuel consumption signal is taken
from terminal 81 on the Engine Control Module
(ECM).
Checking fuel consumption signal

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
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24-181

Coolant temperature signal, checking


Notes:

The engine control module receives the coolant
temperature signal from the instrument cluster.
When the signal is received, the charge
pressure is reduced to prevent the engine from
overheating.

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
.
- Check wiring from test box socket 19 to instrument cluster according to
wiring diagram for an open circuit.
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24-182

Vehicle Speed Signal (VSS), checking


Notes:

The vehicle speed signal is generated by the
Vehicle Speed Sensor (VSS) -G68 (on the
transmission) and is processed in the
instrument cluster.
The processed signal goes to terminal 54 on
the engine control module and is used for Idle
Air Control (IAC) and for the damping of load
change jolts when changing gear.

- Start engine.

- 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 .

- Select "Read measured value block" (function
08) and Display Group 5. Read Measuring Value Block 5
1
2
3
4

Indicated on display:
Warning!
During a road test in an airbag equipped vehicle, VAG1551 must
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always be fastened to and operated from the rear seat by a
second technician. When driving or riding in an airbag equipped vehicle, NEVER hold
the scan tool or other test equipment in your hands or lap while in
motion. Objects between you and and the airbag increase the risk
of injury in an accident.
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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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24-184

Fuel tank level signal, checking


Note:

The Engine Control Module (ECM) receives the
fuel tank level signal from the instrument
cluster.
The processed signal enters on terminal 30 the
Engine Control Module (ECM) and is used to
determine certain malfunctions (e.g.: misfire)

- Connect VAG1598/31 test box to wiring harness
for engine control module. Do not connect to the
engine control module itself Page 24
-20
.

- Check wiring from test box socket 30 to
instrument cluster according to wiring diagram
for an open circuit and short circuit to B+/Ground
(GND).
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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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