1996 AUDI A4 light

24-79


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".
Pa
ge 1 of 61 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.2

24-88

System in Basic Setting 32
1
2
3
4

Indicated on display: (1 - 4 display fields) - Check oxygen sensor control in display fields 1 to
4:

Display fields

1 2 3 4
Display Group 32: Oxygen sensor adaptation at idle speed
Display
xx.x %
x.xxx %
xx.x %
x.xxx %
Indicates
Oxygen sensor
adaptation value, bank
1, sensor 1 at idle
(additive) Oxygen sensor
adaptation value, bank
1, sensor 1 at partial
throttle (multiple) Oxygen sensor
adaptation value, bank
2, sensor 1 at idle
(additive) Oxygen sensor
adaptation value, bank 2,
sensor 1 at partial throttle
(multiple)
Range
min.: -25.0 %
max.: 25.0 % min.: -25.0 %
max.: 25.0 % min.: -25.0 %
max.: 25.0 % min.: -25.0 %
max.: 25.0 %
Specification
-4.0 and 4.0 %
can fluctuate slightly -4.0 and 4.0 %
can fluctuate slightly -4.0 and 4.0 %
can fluctuate slightly -4.0 and 4.0 %
can fluctuate slightly
Note
If readout does not
match specification
Page 24
-90
and Page
24
-91

If readout does not
match specification
Page 24
-90
and Page
24
-91

If readout does not
match specification
Page 24
-90
and Page
24
-91

If readout does not
match specification
Page 24
-90
and Page
24
-91
Pa
ge 10 of 61 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.2

24-101

Notes:

Oxygen sensor control behind the catalytic
converter is responsible for final control
correction. It is the primary sensor and can
override the signal from the oxygen sensor
control before the catalytic converter..

Component location of harness connectors Page 24
-5
It corrects slight changes in the mixture (i.e. enrichment) via the
oxygen sensor before catalytic converter by holding the oxygen
sensor control before catalytic converter at its higher or lower limit for
a specific time (duration). If this time is in the positive range (i.e. 50
ms), mixture is shifted in the -enrich- direction. If this time is in the
negative range (i.e. -50 ms), mixture is shifted in the -lean- direction.
Pa
ge 24 of 61 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.2

24-109


Display fields

1 2 3 4
Display group 037: Diagnostic oxygen sensor control (Bank 1)
Display xxx % x.xxx Volt xxx ms
Test ON
Indicated Engine
load Oxygen sensor voltage behind
catalytic converter, Bank 1 Correction value between
oxygen sensor 1 and sensor
2, bank 1 Diagnostic condition
Work
range 15.0 -
175.0 % 0.000 - 1.000 V -1200 - 1200 ms
Test OFF
Test ON
SYST. OK
SYST. not OK
Specified
value 15.0 -
25.0 % 0.000 - 1.000 V -500 - 500 ms
SYST. OK
Note

If specified value is not
obtained: Evaluation display
field 2 Page 24
-112

If specified value is
obtained: Continuation
Page 24
-113

If "SYST. not OK" is
displayed: Check DTC
memory Page 01
-15

or Continue Page 24-113

Note for display field 3:
Oxygen sensor control behind catalytic converter is superior to oxygen sensor control before catalytic converter and is the
primary control. It corrects slight changes in the mixture (i.e. enrichment or thinning) by holding the oxygen sensor control
before catalytic converter at its higher or lower point for a specific time (duration). If this time is in the positive range (i.e. 50
ms), mixture is shifted in the -enrich- direction. If this time is in the negative range (i.e. 50 ms), mixture is shifted in the -lean-
Pa
ge 35 of 61 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.2

24-111


Display fields

1 2 3 4
Display group 038: Diagnostic oxygen sensor control (Bank 2)
Display xxx % x.xxx Volt xxx ms
Test ON
Indicated Engine
load Oxygen sensor voltage behind
catalytic converter, Bank 2 Correction value between
oxygen sensor 1 and sensor
2, bank 2 Diagnostic condition
Work
range 15.0 -
175.0 % 0.000 - 1.000 V -1200 - 1200 ms
Test OFF
Test ON
SYST. OK
SYST. not OK
Specified
value 15.0 -
25.0 % 0.000 - 1.000 V -500 - 500 ms
SYST. OK
Note
If specified value is not obtained:
Evaluation display field 2
Page 24
-112

If specified value is obtained:
Continuation Page 24
-113

If "SYST. not OK" is
displayed: Check DTC
memory Page 01
-15

or Continue Page 24-113

Note for display field 3:
Oxygen sensor control behind catalytic converter is superior to oxygen sensor control before catalytic converter and is the
primary control. It corrects slight changes in the mixture (i.e. enrichment or thinning) by holding the oxygen sensor control
before catalytic converter at its higher or lower point for a specific time (duration). If this time is in the positive range (i.e. 50
ms), mixture is shifted in the -enrich- direction. If this time is in the negative range (i.e. 50 ms), mixture is shifted in the -lean-
Pa
ge 38 of 61 Ox
yg
en sensor control, checkin
g
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.2