1998 AUDI A8 sensor

24-27

Oxygen Sensor (O2S) heater (before
TWC), checking


Notes:

Harness connector for Oxygen Sensor (O2S)
heater: 4-pin, brown
Component locations Page 24
-1 .

Required special tools and test equipment

VAG 1551 or VAG 1552 Scan Tool (ST) with
VAG 1551/3 adapter cable
VAG 1598/22 test box
Multimeter US 1119 (Fluke 83 or equivalent)
VW 1594 connector test kit
Wiring diagram

Test requirements
Fuse for Oxygen Sensor (O2S) heater OK
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24-29

- Compare display and specified values (display
fields 1 and 2):

Display fields

1 2 3 4
Display group 41: Oxygen Sensor (O2S) heating
Display
xx.x
Htg.bC.ON/Htg.bC.OFF
xx.x
Htg.aC.ON/Htg.aC.OFF
Indicates Resistance of oxygen
sensor heater
(before TWC) O2S heater on
or
O2S heater off
(before TWC) Resistance of oxygen
sensor heater
(after TWC) O2S heater on
or
O2S heater off
(after TWC)
Range
0.0-65.0
--- --- ---
Specified
value 4.9-19.9
Htg.bC.ON --- ---

If not as specified Page 24
-30
, Continuation
--- ---
If displayed values are OK (as specified):

-
Press button to advance program
sequence.
-
Press buttons -0- and -6- to select "End Output"
function 06, and press -Q- button to confirm
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24-30

Continuation

- Disconnect 4-pin connector -1- (brown) for
Heated Oxygen Sensor (HO2S) -G39-.

If resistance is NOT OK: - Connect multimeter US 1119 (Fluke 83 or equivalent) between HO2S
connector terminals 1 and 2, using VW 1594 connector test kit.
- Measure resistance.

Specified value: 0.0-19.9 - Replace Heated Oxygen Sensor (HO2S) -G39-.
Pa
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(MFI
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11/19/2002 htt
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play?action=Goto&t
yp
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pair&id=AUDI.B5.FU02.24.1

24-35

Oxygen Sensor (O2S) behind Three Way
Catalytic Converter (TWC) and oxygen
sensor control, checking


Notes:

Harness connector for Oxygen Sensor (O2S)
behind Three Way Catalytic Converter (TWC):
4-pin, black
Component locations Page 24
-1

Required special tools and test equipment

VAG 1551 or VAG 1552 Scan Tool (ST) with
VAG 1551/3 adapter cable
VAG 1598/22 test box
Multimeter US 1119 (Fluke 83 or equivalent)
VW 1594 connector test kit
Wiring diagram

Test requirements

Pa
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(MFI
) and i
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11/19/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
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pair&id=AUDI.B5.FU02.24.1

24-37

- Compare display and specified values (display
fields 1 and 2):

Display fields

1 2 3 4
Display group 36: Heated Oxygen Sensor (HO2S) behind Three Way Catalytic Converter (TWC)
Display x.xxx V B1-S2 ON
B1-S2 OFF
Indicates Voltage supply to HO2S behind TWC HO2S behind TWC
ON/OFF
Range 0.000-1.000 V ---
Specified value 0.000-1.000 V
(can oscillate slightly) B1-S2 ON

If not as specified Page 24
-38
, Continuation

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24-38

Continuation
If displayed values are NOT OK (not as
specified):

- Road test to condition oxygen sensor (eliminate
possible contamination) and repeat test.
If the values in display fields 1 and 2 are still
NOT OK:

- Check Oxygen Sensor (O2S) heater Page 24
-
43
.

- Briefly accelerate engine over 3000 RPM.
If the value in display field 1 remains constant:
page Page 24
-39
, Evaluation of display group
36.
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24-39
Evaluation of display group 36 Display group:
36


Display field: 1
Possible causes
Corrective action
approx. 0.435
V
Open circuit in wiring -4- between oxygen sensor and ECM - Check basic voltage Page 24
-40
approx. 0.440
V
Open circuit in wiring -4- between oxygen sensor and ECM
approx. 1.085
V Short circuit to B+ in wiring -4- between oxygen sensor
and ECM - Check wiring for oxygen sensor
Page 24
-41

approx. 0.000
V
Short circuit to Ground in wiring -4- between oxygen
sensor and ECM
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24-40

Checking HO2S reference voltage

- Disconnect 4-pin connector (black) for Oxygen
Sensor (O2S) behind Three Way Catalytic
Converter (TWC) -G108-.

If voltage is NOT OK:
If voltage is OK: - Connect multimeter US 1119 (Fluke 83 or equivalent) between harness
connector terminals 3 and 4 (to ECM), using adapter cables from VW
1594 connector test kit.
- Start engine and measure voltage.
Specified value: 0.40 to 0.50 volts
- Switch ignition off.
- Check HO2S wiring Page 24
-41
- Replace HO2S behind TWC -G108-.
Pa
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port Fuel In
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(MFI
) and i
gnition s
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11/19/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU02.24.1