1997 AUDI A4 APB Engine Ignition System Checking

28-15
If the diode test lamp does not flash when testing
one or more of the contacts:
Check the Ground (GND) connections for the
power output stages as follows:

- Disconnect 4-pin harness connectors from
power output stages.

- Connect diode test lamp VAG1527 to battery
(B+) and terminal 2 of each of the 4-pin
connectors in turn.

The diode test lamp should light up.
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28-16

- If diode test lamp does not light up, test for open
circuit in wiring using wiring diagram.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
If the diode test lamp lights up:

- Replace power output stage.

Note:
Before installing new power output stage coat
metal side with heat paste (part no. G 052 170
A1). The heat paste is used to prevent corrosion
between the power output stage and the
fastening point, it is also used to transfer heat
from the power output stage.

CAUTION!

Part numbers are only for reference, always
check with your parts department for latest
information.
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28-17

Intake Air Temperature (IAT) sensor -
G42, checking

Location of sensor and connector Page 24
-5 .

- 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
HELP
Input Displa
y Group Number XXX

Indicated on display
- Press buttons -0-, -0- and -4- to select Display Group 4 and confirm
entry with -Q- button.
Read Measuring Value Block 4
1
2
3
4

Indicated on display: (1...4 display fields) - Check display value for intake air temperature sensor (display field 4):
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28-18


Display fields

1 2 3 4
Display Group 004: Intake air temperature with engine idling
Display xxxx rpm xx.xxx V
xxx.x C
xxx.x C
Indicates Engine speed Battery voltage Coolant temperature
Intake air temperature
Work range min.: 750 RPM
max.: 6800 RPM min.:10.000 V
max.: 15.000 V min.: -48.0 C
max.: 143.0 C
min.: -48.0 C
max.: 143.0 C
Specified value xxxx RPM 12.000...15.000 V
80.0...110.0 C
Between ambient temp. and 120 C
1)
1) If there is a large difference between the temperature displayed and the ambient temperature at the sensor, check the
sensor and sensor wiring for contact resistance and open circuit.
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28-19

Checking wiring:

- Switch ignition off.

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

- Check for open circuit in wiring between test box and 2 pin harness
connector using wiring diagram.

Specified value: max. 1.5
Terminal on 2-pin harness
connector
Contact on control module
connector or test box
1
2 85
108
- Check wiring for short circuits to each other between contacts 1 and 2
on 2-pin connector. Also test for short circuits to B+ or Ground (GND).
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28-20
If no malfunction in wire is detected:

Checking sender

- Measure resistance between contacts 1 (signal) and 2 (Ground GND))
on connector for Intake Air Temperature (IAT) sensor -G42. Temperature C
Resistance k
-20 approx. 13.8
0 approx. 5.5
20 approx. 2.4
40 approx. 1.1
60 approx. 0.6
- If value does not match the specification, replace intake air
temperature sensor.
- In order to install a new sensor, the intake manifold must first be
removed Page 24
-15
.
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28-21

Engine Speed (RPM) sensor -G28,
checking


Note:

The engine speed sender is a combined speed
sender and reference mark sender. Without a
signal from the Engine Speed (RPM) sensor -
G28 the engine cannot be started. If the signal
from the Engine Speed (RPM) sensor -G28 fails
while the engine is running, the engine will cut
out immediately.

Checking Engine Speed (RPM) sensor
Component location of sensor and connector
Page 24
-5 .

- Before carrying out test, make sure that sensor
is correctly installed and firmly seated.

- Disconnect harness connector for Engine Speed
(RPM) sensor (grey connector).
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28-22


Notes:
If the specification is not attained:
If the specification is attained:
If the specification is not attained:
If the specification is attained: - Connect multimeter (Fluke 83 or equivalent) (resistance test range) to
terminals 2 and 3 on connector for engine speed sensor using test lead
from VAG1594 connector test kit.
Specified value: approx. 730 - 1000 ohm
The resistance value for the engine speed sensor is based on a
temperature of 20 C. The resistance increases as the temperature rises.
- Replace engine speed sensor.
- Connect multimeter (Fluke 83 or equivalent) (resistance test range)
between terminals 2 and 1 (Ground (GND)) and between terminals 3
and 1 (Ground (GND)).

Specified value: R (infinite Ohms / open circuit) in each test
- Replace Engine Speed (RPM) sensor.
-
Check wiring between sensor connector and engine control module as
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