Page 1 of 61
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Oxygen sensor control,
checking
Function of oxygen sensor control
The oxygen sensors compare the oxygen
content in the air with the residual oxygen
content in the exhaust gas and send a voltage
signal to the control module.
The voltage signal for "Mixture too rich" (low
residual oxygen) is between about 0.5 and 1.0 V
(relative to reference Ground (GND)).
The voltage signal for "Mixture too lean" (high
residual oxygen) is between about 0 and 0.5 V
(relative to reference Ground (GND)).
The transition from "rich" to "lean" is
accompanied by a voltage jump from between
0.5 and 1.0 V to between 0 and 0.5 V (relative to
reference Ground (GND)), and vice versa ( =
1.0).
Because of the sharp voltage jump the oxygen
sensor control cannot maintain a constant ideal
mixture composition of = 1.0. The system
fluctuates continuously between "slightly too
lean" and "slightly too rich".
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Page 2 of 61
24-80
If the voltage does not change or only changes
slowly the following malfunctions are possible:
Slits or holes in probe head are blocked.
Oxygen sensor has been subjected to
excessive thermal stress.
Contact resistance in signal wire or Ground
(GND) wire.
Oxygen sensor too cold; sensor heater not
working.
Oxygen sensor damaged by contact spray or
similar product. (The contact spray is drawn
through the fine cavities in the electrical wiring
as a result of thermal fluctuations and capillary
effect.)
Oxygen sensor damaged by silicone vapors.
(The engine draws in traces of any silicone-
based sealants that may have been used. The
silicone does not burn and damages the oxygen
sensor.)
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Page 3 of 61
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Oxygen sensor and oxygen sensor control
before Three Way Catalytic Converter
(TWC), checking
Special tools and shop equipment
Fluke 83 (or equivalent) A
VAG1594 A
VAG1598/31
VAS5051 with VAS5051/1
- or
VAG1551 with VAG1551/3B
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Notes:
For the defined troubleshooting procedure, it is
possible to switch off the oxygen sensor control
by selecting Display Group 99 in "Basic Setting"
mode and to switch it on again by selecting
Display Group 99 in "Read Measuring Value
Block" mode.
After selecting Display Group 99 (either in
"Basic Setting" mode or in "Read Measuring
Value Block" mode) it is possible to switch back
and forth between function 04 ("Basic Setting")
and function 08 "Read Measuring Value Block")
by pressing buttons 4 and 8 on VAG1551 scan
tool.
When exiting the "Basic Setting" mode (function
04) the oxygen sensor control is automatically
switched on again.
Test conditions
Perform road test and do not erase DTC
memory.
Coolant temperature at least 85 C (Display
group 004, display field 3)
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Page 5 of 61
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Checking function
- Connect vehicle diagnostic, testing and
information system VAS5051 or VAG1551 scan
tool and select engine electronics control
module by entering address word "01" Page
01
-9 . When doing this the engine must be at
idle.
Rapid data transfer
HELP
Select function XX
Indicated on display
Note:
During the basic setting the Evaporative Emission (EVAP) canister purge
regulator valve -N80 is closed and the A/C compressor is switched off. - Press buttons -0- and -4- to select function "Basic Setting" and confirm
entry with -Q- button.
Basic Settin
g
Input displa
y group number XXX
Indicated on display
- Press buttons -0-, -3- and -0- to select "display group number 030" and
confirm entry with -Q- button.
System in Basic Setting 30
1
2
3
4
Indicated on display: (1 - 4 display fields) - Check oxygen sensor status in display fields 1 to 4.
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Page 6 of 61
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Note:
The "Oxygen sensor status" display indicates the
status of the oxygen sensor control and oxygen
sensors.
Display fields
1 2 3 4
Display Group 030: Oxygen sensor status at idle speed (coolant temperature at least 85 C)
Display
0 0 0 0 0 0
0 0 0 0 0 0
Indicates
Oxygen sensor status
bank 1, sensor 1 Oxygen sensor status
bank 1, sensor 2 Oxygen sensor status
bank 2, sensor 1 Oxygen sensor status
bank 2, sensor 2
Work range
0 = off
1 = on 0 = off
1 = on 0 = off
1 = on 0 = off
1 = on
Specification
1 1 1 0 1 0
1 1 1 0 1 0
Note
Significance of display Page 24
-85
If specification is obtained, but a malfunction is stored in the DTC memory: Check oxygen sensor
adaptation values and oxygen sensor control Page 24
-86
If specification is not obtained: Check oxygen sensor signal wire and activation Page 24
-122
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Page 7 of 61
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Significance of 3 digit indication in Display Group 30 1
1
1
Display fields 1 through 3
X Oxygen sensor control
0= inactive
1= active
X Operational readiness of oxygen sensor
0= inactive
1= active
X Condition of oxygen sensor heater
0= inactive
1= active
Note:
The oxygen sensor control for oxygen sensors behind the catalytic converter (B1-S2 and B2-S2) are without engine load
at certain operating conditions not active, that means, the third place of oxygen sensor control for oxygen sensors behind
the catalytic converter can fluctuate between 0 and 1.
The first position of the 3 digit display (Heater) fluctuate at certain operating conditions between 0 and 1.
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Page 8 of 61
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Checking oxygen sensor adaptation and
oxygen sensor control
- Connect vehicle diagnostic, testing and
information system VAS5051 or VAG1551 and
select engine electronics control module by
entering address word "01" Page 01
-9. When
doing this the engine must be idling.
Rapid data transfer
HELP
Select function XX
Indicated on display
Note:
During the basic setting the Evaporative Emission (EVAP) canister purge
regulator valve -N80 is closed and the A/C compressor is switched off. - Press buttons -0- and -4- to select function "Basic Setting" and confirm
entry with -Q- button.
Basic Settin
g
Input displa
y group number XXX
Indicated on display
- Press buttons -0-, -3- and -3- to select Display Group 33 and confirm
entry with -Q- button.
System in Basic Setting 33
1
2
3
4
Indicated on display: (1 - 4 display fields)
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