1997 AUDI A4 catalytic converter

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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11/22/2002 htt
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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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24-99


Display on VAS5051:
Checking oxygen sensor control after catalytic converter
Test requirement: - Do not continue test until indication in display field -2- has reached
"110" at least once.
Engine continues to run at 2600 RPM.
-
Click on - button

Display on VAS5051:
1 - Enter display group Max. input value = 255
- Select function "037" in button field -2- for "display group number 037"
and press -Q- button to confirm input.
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p://127.0.0.1:8080/audi/servlet/Dis
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24-101


Display fields

1 2 3 4
Display group 037: Diagnostic oxygen sensor control system
Display xxx %
x.xxx V
x.xx
---
Indicated Engine
load Oxygen sensor voltage
Bank 2, sensor 1 Oxygen sensor correction value
between bank 1, sensor 1 and
bank 1, sensor 2 Diagnostic condition
Functional
range


Test OFF
Test ON
System OK
System not OK
Specified
value 13 to 40
% 0.100 to 0.950 volts
smaller than 0.02 System OK
Note

If specified value is not
obtained: Evaluation
Page 24
-102


If "System not OK" is
displayed: Check DTC
memory Page 01
-12

Note for display field 2:
Oxygen sensor voltage bank 1, sensor 2 should remain fairly constant. Strong voltage fluctuations point to a damaged
catalytic converter.
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
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24-102
Evaluation display group 037 Display field: 2
Possible cause
Corrective action
constant about
0.450 V
Open circuit in wire 4 between oxygen sensor
and control module - Check primary voltage Page 24
-104


Open circuit in wire 3 between oxygen sensor
and control module
larger than
0.950 V Short circuit to B+ in wire 4 between oxygen
sensor and control module - Check oxygen sensor wiring, oxygen sensor after
catalytic converter Page 24
-105

smaller than
0.100 V
Short circuit to Ground (GND) in wire 4 between
oxygen sensor and control module
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24-103

Continuation
If specified value in display field 3 and 4 is not
obtained:

- Road test vehicle in order to free oxygen sensor
of possible residue and repeat test.
If specified value in display field 3 and 4 is not
obtained, even after road test:

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

Note:
If oxygen sensor voltage is OK and oxygen
sensor correction value is still above 0.02 ms,
even after a road test, this suggests aging of an
oxygen sensor before catalytic converter.
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ge 35 of 46 Ox
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11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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pair&id=AUDI.B5.FU07.24.2

24-104

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

- Connect multimeter between terminal 3 and 4 for voltage
measurement.
- Switch ignition on.

Specification: 0.400 to 0.500 V
- Switch ignition off.
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24-105
If specified value is not obtained:

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

- Replace Oxygen Sensor (O2S) behind Three
Way Catalytic Converter (TWC) -G130-.

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 4-pin harness connector -1- (brown) to Oxygen Sensor
(O2S) behind Three Way Catalytic Converter (TWC) -G130-.
- Connect VAG1598/31 test box at wiring harness to Engine Control
Module (ECM), do not connect ECM Page 24
-19
.
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ge 37 of 46 Ox
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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