AUDI A6 1995 C5 / 2.G ATQ Engine Oxygen Sensor Control Checking

24-76


Oxygen sensor control,
checking

Oxygen sensor control, function


Notes:
The oxygen sensors compare the oxygen
content of the air with residual oxygen content in
exhaust and deliver a voltage signal to the
control module.
The voltage signal "mixture rich (too little residual
oxygen)" is approx. 0.7 to 1.0 V.
The voltage signal "mixture lean (a lot of residual
oxygen)" is approx. +0.0 to 0.3 V.
At the transition from "rich" to "lean" and vice-
versa ( = 1.0) voltage will jump from 0.7 to 1.0
V to 0.0 to +0.3 V (or viceversa).
Due to the steep voltage jump, oxygen sensor
control cannot maintain the ideal mixture of =
1.0 as constant. Oxygen sensor control
constantly fluctuates back and forth between the
conditions "slightly too lean" and "slightly too
rich".
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If voltage change does not occur or occurs only
slowly, the following malfunctions could be
present:

Slits or holes in sensor head clogged.
Sensors suffered thermal overload.
Transition resistance in signal wire or Ground
(GND) wire.
Sensor too cold, sensor heating not
functioning.
Sensor damaged by contact spray or similar
substance (contact spray is drawn through the
fine hollow interiors by thermal fluctuations and
capillary action into the electrical wiring in
sensor).
Sensor damaged by silicon vapors (the use of
sealants containing silicon leads to trace
elements of silicon being taken in by the
engine. These silicon elements are not
combusted and damage the oxygen sensor).
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Oxygen sensors and oxygen sensor
control before catalytic converter,
checking

Special Tools and Equipment

VAG1526A
VAG1594A
VAG1598/31
VAS5051 with VAG5051/1
- or
VAG1551 with VAG1551/3B
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Notes:

For the defined troubleshooting procedure, it is
possible, to switch oxygen sensor control off by
selecting display group 099 under "basic
setting" and switch it on again under "read
measuring value block".
After selecting display group 099 (either in
"basic setting" or "read measuring value
block"), it is possible to switch back and forth
between "basic setting" (function 04) and "read
measuring value block" (function 08) by
pressing buttons 4 or 8 on the VAG1551.
Once function 04 "basic setting" is exited,
oxygen sensor control is automatically switched
on again.

Test requirements:
Road test performed and DTC memory
erased.
Coolant temperature at least 80 C
Display group 4, display field 3
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24-80

Function test

- Connect VAS5051 tester or VAG1551 scan tool
and select the control module for engine
electronics using "address word" 01 Page 01
-
9 .

Engine must run at idle for this.Rapid data transfer
HELP
Select function XX

When indicated on display:
Note:
During basic setting, the Evaporative Emission (EVAP) canister purge
regulator valve (EVAP valve -N80-) is closed and the A/C compressor is
switched off - Press buttons -0- and -4- to select "Initiate basic setting" and press -Q-
button to confirm input.
Basic Settin
g
Q
Input displa
y group number XXX

When indicated on display:
- Press buttons -0-, -3- and -0- to select "display group number 030" and
press -Q- button to confirm input.
System in Basic Setting 30
1
2
3
4

When indicated on display:
Note: - Check oxygen sensor status in display fields 1 and 3.
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"Oxygen sensor status" indicates status of oxygen sensor control and
oxygen sensors.
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Display fields

1 2 3 4
Display group 030: Oxygen sensor status with engine at idle
Display
X X X X X X
X X X X X X
Indicated
Oxygen sensor status,
bank 1, sensor 1 Oxygen sensor status,
bank 2, sensor 1 Oxygen sensor status,
bank 2, sensor 1 Oxygen sensor status,
bank 2, sensor 2
Functional
range 0 = off
1 = on 0 = off
1 = on 0 = off
1 = on 0 = off
1 = on
Specified
value 1 1 1 1 1 0
1 1 1 1 1 0
Notes
Meaning of display Page 01
-90

If specified value is not obtained Page 24
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If specified value is obtained but there is a malfunction stored in DTC memory Check oxygen
sensor adaptation values and control, page Page 24
-83

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Significance of 3 digit indication of display group 030 X
X
X
Display fields 1 to 4
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 heating
0= not active
1 = active
Notes:

The oxygen sensor control of the oxygen sensors behind catalytic converter (B1-S2 and B2-S2) are not active at certain
operation points without engine load, that means that the third position of the oxygen sensor controls behind catalytic
converter can fluctuate between 0 and 1.
The first position of the 3 digit indication (heating) fluctuates between 0 and 1 at certain operation points.
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Checking oxygen sensor adaptation values
and control

- Press -C- button.Basic Setting
Q
Input displa
y group number XXX

When indicated on display:
- Press buttons -0-, -3- and -3- to select "display group number 033" and
press -Q- button to confirm input.
System in Basic Setting 33
1
2
3
4

When indicated on display:
- Check oxygen sensor control in display fields 1 and 3.
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1 2 3 4
Display group 033: Oxygen sensor control before catalytic converter
Display
xx.x % x.xxx volts
xx.x % x.xxx V
Indicated
Oxygen sensor control
Bank1 Oxygen sensor voltage
bank 1 Oxygen sensor control
Bank2 Oxygen sensor voltage
bank 2
Functional
range -25.0 to 25.0 % 0.100 to 1.000 V
-25.0 to 25.0 % 0.100 to 1.000 V

Specified
value Value must fluctuate by
at least 2 % in the range
10.0 to 10.0 % Value must fluctuate
approx. 0.3 V in the
range 0.100 to 1.000
volts Value must fluctuate by
at least 2 % in the range
10.0 to 10.0 % Value must fluctuate
approx. 0.3 V in the
range 0.100 to 1.000
volts
Notes
If specified value is not
obtained Page 24
-85


If specified value is not
obtained Page 24
-85


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