2000 AUDI A8 sensor

24-15
Evaluation of 6-digit display:

"1" = Adjustment conditions fulfilled
"0" = Adjustment conditions not fulfilled
If adjustment conditions have been fulfilled (indicated in display field 4), a series of 6 numerals ("1") will be displayed. If
one of the digits in the 6-digit display is "0," the adjustment condition has not been fulfilled. Repair the cause of the
unfulfilled condition, and repeat the test.
Explanation (display = 1)
x
x
x
x
x
x
Adjusting conditions (display group 1)
1
Engine Coolant Temperature (ECT) above 80 C
1 Engine speed less than 2000 RPM
1 Throttle valve closed
1 Oxygen sensor control active
1 Closed Throttle Position (CTP) switch closed
1 A/C compressor off
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24-17

Heated Oxygen Sensor (HO2S) and
oxygen sensor control (before TWC),
checking


Notes:

Connector for Heated Oxygen Sensor (HO2S)
before Three Way Catalytic Converter (TWC):
4-pin, brown
Component location 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 conditions

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24-19

- Check oxygen sensor control learning values
(display fields 1 and 2):

Display fields

1 2 3 4
Display group 32: Oxygen sensor control learning values
Display xx.x % xx.x %
Indicates Oxygen sensor control learning value at idle
(additive)
(before TWC) Oxygen sensor control learning value at partial load
(multiplicative)
(before TWC)
Range -26.0 to 26.0 % -25.0 to 25.0 %
Specified
value -8.0 to 8.0 %
(can vary slightly) -8.0 to 8.0 %
(can vary slightly)
If not as specified Page 24
-22
, Evaluation of display group 32

If displayed values are OK (as specified):

- Press -C- button.

- Press buttons -0-, -3- and -3- to input display
group number 33, and press -Q- button to
confirm input. Read Measuring Value Block 33

Indicated on display (1-4 = display fields)
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24-20

- Check oxygen sensor control (display fields 1
and 2):

Display fields

1 2 3 4
Display group 33: Oxygen sensor control
Display xx.x % x.xxx V
Indicates Oxygen sensor control
(before TWC) Oxygen sensor voltage
(before TWC)
Range -25.0 to 25.0 % 0.000-1.000 V
Specified
value Within the range from -10.0 to 10.0 %
the value must change by at least 2 % Within the range from 0.000 to 1.000 V the value must
fluctuate at least 30 times per minute, and change by at
least 0.3 volts

If not as specified Page 24
-21
,
Continuation
If not as specified Page 24
-23
, Evaluation of display
group 33

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24-21

Continuation
If the value in display field 1 is NOT OK, or if the
value does not fluctuate by at least 2 %:

- Road test to condition oxygen sensor (eliminate
possible contamination) and repeat test.
If the value in display field 1 is still NOT OK, or if
it still does not fluctuate by at least 2 %:

- Check Oxygen Sensor (O2S) heater Page 24
-
27
.
If the value in display field 1 remains constant:

- Check oxygen sensor voltage (display field 2).

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

- Switch ignition off.
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24-22
Evaluation of display group 32 Display group:
32


Display fields: 1
+ 2
Possible cause
Corrective action
O2S control
learning value:
-26.0 to -8.0 %
Engine oil dilution (when partial load learning value
is normal, display field 2)
- Change engine oil, or carry out extensive road
test and check again.


Fuel pressure too high- Check fuel pressure regulator Page 24
-93


Fuel injector leaking- Check fuel injectors Page 24
-87


Oxygen Sensor (O2S) heater malfunction- Check O2S heater Page 24
-27
O2S control
learning value:
8.0-26.0 %
Intake air leaks ("false air") or exhaust manifold
leaks (when partial load learning value is normal,
display field 2)
Repair Manual, 1.8 Liter 4
-Cyl. 5V Turbo
Engine Mechanical, Engine Code(s): AEB, ATW, Repair Group 26
- Check intake air system for leaks Page 24
-
97

- Check exhaust system for leaks:


Fuel pressure too low- Check fuel pressure regulator Page 24
-93


Oxygen Sensor (O2S) heater malfunction- Check O2S heater Page 24
-27
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Fuel injector does not open, or partially opens- Check fuel injectors Page 24
-87
O2S control
learning value:
constant 0.0 %
Oxygen sensor control learning not active- Check Mass Air Flow (MAF) sensor -G70-
Page 24
-57

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24-24

Checking HO2S reference voltage

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

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: 0.40-0.50 volts
- Switch ignition off.
- Check HO2S wiring Page 24
-25
- Replace Heated Oxygen Sensor (HO2S) -G39-.
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