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

24-80
If the voltage does not change or only changes
slowly the following malfunctions are possible:

Slits or holes in probe head are blocked.
Oxygen sensor has been subjected to
excessive thermal stress.
Contact resistance in signal wire or Ground
(GND) wire.
Oxygen sensor too cold; sensor heater not
working.
Oxygen sensor damaged by contact spray or
similar product. (The contact spray is drawn
through the fine cavities in the electrical wiring
as a result of thermal fluctuations and capillary
effect.)
Oxygen sensor damaged by silicone vapors.
(The engine draws in traces of any silicone-
based sealants that may have been used. The
silicone does not burn and damages the oxygen
sensor.)
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24-92
Evaluation display group 33 Display Group
33


Display field:
2/4
Possible cause
Corrective action
Approx. 0.450
V
Open circuit in wire 4 between oxygen sensor and
control module - Check signal wire and activation Page 24
-
122



Open circuit in wire 3 between oxygen sensor and
control module

Oxygen sensor heater faulty
Oxygen sensor faulty- Check oxygen sensor heater Page 24
-114
- Replace oxygen sensor
More than
1.100 V
Short to B+ in wire 4 between oxygen sensor and
control module - Check oxygen sensor wiring, bank 1, sensor
1 Page 24
-123

Less than
0.100 V
Short to Ground (GND) in wire 4 between oxygen
sensor and control module - Check oxygen sensor wiring, bank 2, sensor
1 Page 24
-127

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24-112
Evaluation display group 037 and 038 Display Group:
037/038


Display field: 2
Possible cause
Corrective action
approx.: 0.450 V

Open circuit in wire 4 between oxygen sensor
and control module - Check signal wire and activation Page 24
-
122



Open circuit in wire 3 between oxygen sensor
and control module

Oxygen sensor heater faulty
Oxygen sensor faulty- Check oxygen sensor heater Page 24
-114
- Replace oxygen sensor
greater than
1.100 V
Short circuit to B+ in wire 4 between oxygen
sensor and control module - Check oxygen sensor wiring bank 1 sensor 2
(behind converter) Page 24
-125

smaller than
0.100 V
Short circuit to Ground (GND) in wire 4 between
oxygen sensor and control module
Short circuit between wire 3 and 4- Check oxygen sensor wiring bank 2 sensor 2
(behind converter) Page 24
-129

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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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24-120

Heated Oxygen Sensor (HO2S) -G39
Connector on wiring
harness, socket
VAG1598/31 test
box, socket
2 5 (Ground)
Heated Oxygen Sensor (HO2S) 2 -G108
Connector on wiring
harness, socket
VAG1598/31 test
box, socket
2 4 (Ground)
Oxygen Sensor (O2S) Behind Three Way
Catalytic Converter (TWC) -G130
Connector on wiring
harness, socket
VAG1598/31 test
box, socket
2 63 (Ground)
Oxygen Sensor (O2S) 2 Behind Three Way
Catalytic Converter (TWC) -G131
Connector on wiring
harness, socket
VAG1598/31 test
box, socket
2 6 (Ground)
Resistance in wiring: max. 1.5 Ohm

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
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24-121
If the wiring is OK but the oxygen sensor heater
still has no Ground (GND) connection:

- Replace particular oxygen sensor.

- Display readiness code Page 01
-101
. The
readiness code must be generated if the DTC
memory was erased Page 01
-105
.
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24-122

Oxygen sensor signal wire and
activation, checking


Note:
The oxygen sensor signal is monitored by the
OBD system.

- Check DTC memory Page 01
-15
.

- If a oxygen sensor malfunction is displayed and
the oxygen sensor heater is OK, disconnect
harness connector for relevant oxygen sensor.
Component location of 4-pin harness connector
of oxygen sensor Page 24
-5 .

If the Specified value is not obtained, check oxygen sensor wiring: - Test voltage by connecting hand-held multimeter Fluke 83 (or
equivalent) (measuring range 2 V) between sockets 3 and 4 of
connector on wiring harness.
-
Switch ignition on. Specified value: 450 50 mV. Bank 1, Sensor 1 Page 24
-123
.
Bank 1, Sensor 2 Page 24
-125
.
Bank 2, Sensor 1 Page 24
-127
.
Bank 2, Sensor 2 Page 24
-129
.
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24-123
If Specified value is obtained:

- Replace relevant oxygen sensor.

Checking oxygen sensor wiring for Heated
Oxygen Sensor (HO2S) -G39
Component location of 4-pin harness connector
of oxygen sensor Page 24
-5 .

- Disconnect 4-pin connector (black) for Heated
Oxygen Sensor (HO2S) -G39.

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

Electrical Wiring Diagrams, Troubleshooting & Component Locations - Check following wiring connections for open circuits:
Connector on wiring harness,
socket
VAG1598/31 test box socket

3 51
4 70
Resistance in wiring: max. 1.5 Ohm
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