1998 AUDI A4 heating

24-94

Heated Oxygen Sensor (HO2S) and
oxygen sensor control after Three Way
Catalytic Converter (TWC), checking


Note:
The oxygen sensor before catalytic converter
(bank 1, sensor 1) regulates to Lambda 1. If this
oxygen sensor is damaged, e.g. due to soiling or
overheating, the regulation value may have
shifted. Deviations from Lambda 1 are detected
by the oxygen sensor after catalytic converter
(bank 1, sensor 2). If it recognizes the deviations
downward or upward, it influences the regulation
before catalytic converter, generally increasing or
decreasing it respectively.
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Display fields

1 2 3 4
Display group 030: Oxygen sensor status
Display X X X
X X X

Indicated Oxygen sensor status, bank 1, sensor 1
Oxygen sensor status bank 2, sensor 1

Functional range 0 = off
1 = on 0 = off
1 = on

Specified value 1 1 1
1 1 0

Note
If specified value is not obtained Page 24
-107

Significance of 3 digit indications in display group 030 X
X
X
Display fields 1 and 2
X Oxygen sensor control: 0= not active; 1 = active
X Operational readiness of oxygen sensor: 0= not active; 1 = active
X Condition of oxygen sensor heater: 0= not active; 1 = active
Notes:

The first position of the 3 digit indication (heating) fluctuates between 0 and 1.
Oxygen sensor control of oxygen sensor after catalytic converter (B1-S2) is not active without engine load.
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24-107


Oxygen sensor heating, Oxygen Sensor
(O2S) Heater 1 -Z29- after catalytic
converter, checking

Special Tools and Equipment

VAG1526A
VAG1594A
VAG1598/31
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24-108

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 4-pin harness connector -1- (brown) to Oxygen Sensor
(O2S) behind Three Way Catalytic Converter (TWC) -G130-.

If specified value is not obtained: - Connect multimeter between terminal 1 and 2 for resistance
measurement.

Specified value at room temperature: 6.4 to 47.5
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24-109
If specified value is obtained:

- Check voltage supply of oxygen sensor
heating.

Checking voltage supply for oxygen sensor
heating

Note:
When the Engine Control Module (ECM) switches oxygen sensor heating
on and off, it may be observed via the function "read measuring value
block", in display group number 041 display field 4.
If there is no voltage: - Connect multimeter between terminal 1 (B+) and 2 (Ground -GND-) for
voltage measurement.
- Start engine.

Specification: approx. battery voltage

- Connect multimeter for voltage measurement as follows:Harness connector
Terminal
Measure to
1 (B+) Vehicle Ground (GND)
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24-111
If there is no voltage:

- Connect VAG1598/31 test box at wiring harness
to Engine Control Module (ECM), do not connect
ECM Page 24
-19
.

If wire connection is OK, but there is no Ground (GND) supply for oxygen
sensor heating: - Check the following wire connection for open circuit:Harness connector
Terminal
VAG1598/31 test box
Socket
2 63
- Repair open circuit if necessary.
- Replace Engine Control Module (ECM) Page 24
-22
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