1998 AUDI A4 catalytic converter

24-71


Oxygen sensor control,
checking Oxygen sensor and oxygen sensor control
before catalytic converter, checking

Special Tools and Equipment

VAG1526A
VAG1594A
VAG1598/31
VAS5051 with VAG5051/1
Pa
ge 1 of 46 Ox
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en sensor control, checkin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU07.24.2

24-77

Continuation
If specified value in display field 1 is not obtained
or if value does not fluctuate at least 2 %:

- Road test vehicle in order to free oxygen sensor
of possible residue and repeat test.
If specified value in display field 1 is not obtained
even after road test or if value does not fluctuate
at least 2 %:

- Check primary voltage Page 24
-81
.

- Test oxygen sensor heater before catalytic
converter Page 24
-89
.

- Check oxygen sensor before catalytic converter
for aging Page 24
-84
.
Pa
ge 7 of 46 Ox
yg
en sensor control, checkin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU07.24.2

24-80
Evaluation display group 033 Display field:
2
Possible cause
Corrective action
larger than
4.800 V
Short circuit to B+ in wire connections between
oxygen sensor and control module
Oxygen sensor faulty- Check oxygen sensor wires of oxygen sensor
before catalytic converter Page 24
-82

smaller than
0.130 V
Short circuit to Ground (GND) in wire connections
between oxygen sensor and control module
Oxygen sensor faulty
- Replace oxygen sensor before catalytic
converter
Pa
ge 10 of 46 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU07.24.2

24-81

Checking primary voltage

Note:
Coolant reservoir screws must be removed and coolant reservoir must be
placed to side in order to access the harness connector. The coolant
hoses can remain connected. - Disconnect 6-pin harness connector (black) -2- to Heated Oxygen
Sensor (HO2S) -G39- before catalytic converter.

- Connect multimeter between terminal 1 and 5 for voltage
measurement.
- Switch ignition on.

Specification: 0.400 to 0.500 V
- Switch ignition off.
Pa
ge 11 of 46 Ox
yg
en sensor control, checkin
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU07.24.2

24-82
If specified value is not obtained:

- Check oxygen sensor wiring.
If specified value is obtained:

- Replace Heated Oxygen Sensor (HO2S)-G39-
.

Checking oxygen sensor wires

Note:
Coolant reservoir screws must be removed and coolant reservoir must be
placed to side in order to access the harness connector. The coolant
hoses can remain connected. - Disconnect 6-pin harness connector (black) -2- to Heated Oxygen
Sensor (HO2S) -G39- before catalytic converter.
- Connect VAG1598/31 test box at wiring harness to Engine Control
Module (ECM), do not connect ECM Page 24
-19
.
Pa
ge 12 of 46 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU07.24.2

24-84

Oxygen sensor aging, oxygen sensor
before catalytic converter, checking


Special Tools and Equipment

VAG1788/10 RPM adjuster

Test requirement:
VAS5051 with VAG5051/1Coolant Temperature at least 80 C.
Pa
ge 14 of 46 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU07.24.2

24-89


Oxygen sensor heating, Oxygen Sensor
(O2S) Heater -Z19- before catalytic
converter, checking

Special Tools and Equipment

VAG1526A
VAG1594A
VAG1598/31
Pa
ge 19 of 46 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU07.24.2

24-90

Test requirements:

Coolant Temperature at least 80 C.

Fuse for oxygen sensor heating OK

Electrical Wiring Diagrams, Troubleshooting &
Component Locations

Test sequence

Note:
Coolant reservoir screws must be removed and coolant reservoir must be
placed to side in order to access the harness connector. The coolant
hoses can remain connected. - Disconnect 6-pin harness connector (black) -2- to Heated Oxygen
Sensor (HO2S) -G39- before catalytic converter.

If specified value is not obtained: - Connect multimeter between terminal 3 and 4 for resistance
measurement.

Specified value at room temperature: 2.5 to 10
Pa
ge 20 of 46 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU07.24.2