battery AUDI A4 1995 B5 / 1.G APB Engine Oxygen Sensor Control Checking Workshop Manual

24-117

Checking voltage supply for oxygen sensor
heater
Component location of 4-pin harness connector
of oxygen sensors Page 24
-5 .

- Check fuse for oxygen sensor heater

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
- Disconnect 4-pin harness connector of particular
oxygen sensor.

If there is no voltage reading: - Connect hand-held multimeter (voltage measurement range) between
sockets 1 (B+) and 2 (Ground (GND)) using test leads from VAG1594
connector test kit.
- Operate starter briefly.
Specified value: approx. battery voltage
- Connect hand-held multimeter (voltage measurement range) between
socket 1 (B+) and vehicle Ground (GND) using test leads from
VAG1594 connector test kit.
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24-118

- Operate starter briefly.

Specified value: approx. battery voltage
If there is still no voltage reading:

- Check for open circuit and/or short circuit in
wiring between fuel pump relay and socket 1 on
the relevant oxygen sensor connector (on wiring
harness) via fuse.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations If the voltage supply is OK:

- Connect hand-held multimeter (voltage measurement range) between
socket 2 (switched Ground (GND) connection from engine control
module) and B+ terminal using test leads from VAG1594 connector test
kit.
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24-119

- Start engine.

Specified value: approx. battery voltage
(fluctuating)

Note:
At certain points in the operating range the
engine control module continuously "switches"
the Ground (GND) connection to the oxygen
sensor heater. That means, it repeatedly
connects and disconnects the Ground (GND)
connection at these points. For this reason the
voltage reading on the tester may fluctuate.

- Switch ignition off.
If there is no voltage reading:

- 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 for open circuits in the following wiring connection:
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