AUDI A4 1996 B5 / 1.G AFC Engine Oxygen Sensor Control Checking Before Converter Workshop Manual

24-45


Oxygen Sensor (O2S) control,
checking (before three way
catalytic converter)

Note:

G39 = Heated Oxygen Sensor (HO2S), bank
1
G108 = Heated Oxygen Sensor (HO2S) 2, bank
2

- Read measuring value block using VAG 1551
scan tool until display shows "Read measuring
value block 1" (display group 001) Repair
Group 01.
Read measuring value block 1 1 2 3 4

Indicated on display
Note:
Continue with the test only if the value in display field 1 (engine coolant
temperature) is at least 80 C (176 F). - Press -C- button.
- Press buttons -0-, -1- and -0- to input display group 010.
- Press -Q- button to confirm input.
Read measuring value block 10

Indicated on display
Pa
ge 1 of 7 Ox
yg
en Sensor
(O2S
) control, checkin
g (before three wa
y catal
ytic converter
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.24.11

1 2 3 4
Display fields 3 and 4 show the signal voltages of both heated oxygen
sensors.
If sensor voltage fluctuates very slowly page 24
-41
.
Pa
ge 2 of 7 Ox
yg
en Sensor
(O2S
) control, checkin
g (before three wa
y catal
ytic converter
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.24.11

24-46
If a constant sensor voltage of 0.000V is
displayed, there is a short to Ground (GND).

- Check DTC memory Repair Group 01. If sensor voltage is constant between 0.350 and
0.450 volts, the signal is interrupted:

- Check DTC memory page 01
-13
.
If sensor voltage is a constant 2.550 volts, there
is a short to battery positive voltage (B+):

- Check DTC memory page 01
-13
.

- If sensor voltage is a constant 0.0 to 0.3 volts,
the oxygen sensor measures a lean mixture:

- Check DTC memory page 01
-13
.

- If sensor voltage is a constant 0.6 to 0.9 volts,
the oxygen sensor measures a rich mixture:

- Check DTC memory page 01
-13
.

- Press -C- button.Read measuring value block
Q

- Indicated on display
Pa
ge 3 of 7 Ox
yg
en Sensor
(O2S
) control, checkin
g (before three wa
y catal
ytic converter
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.24.11

Input displa
y group number XXX
Pa
ge 4 of 7 Ox
yg
en Sensor
(O2S
) control, checkin
g (before three wa
y catal
ytic converter
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.24.11

24-47
With a properly functioning oxygen sensor, the
actual control learning values can be checked.
Various malfunctions (e.g. intake air leakage,
faulty fuel injectors etc.) can cause a change in
the mixture composition. These malfunctions are
recognized by the oxygen sensor and are
corrected via oxygen sensor control by adjusting
the fuel injection time via the ECM. Fuel injection
time that deviates from the programmed basic
fuel injection time indicates a malfunction of
some type.
These deviations are shown (oxygen sensor
control learned values) in display group 005
(bank 1) or 006 (bank 2). There is a deviation
between idle and partial load readings; the
deviation between actual fuel injection times and
the programmed basic settings are indicated as a
percentage (%).

Positive oxygen sensor control learned
values (+%):
Programmed basic fuel injection time too short
(mixture too lean), actual fuel injection time
by ...% longer , so that = 1 can be obtained.
Negative oxygen sensor control learned value
(-%):
Programmed basic fuel injection time too long
(mixture too rich) , actual fuel injection time
Pa
ge 5 of 7 Ox
yg
en Sensor
(O2S
) control, checkin
g (before three wa
y catal
ytic converter
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.24.11

by ...% shorter, so that = 1 can be obtained.
Pa
ge 6 of 7 Ox
yg
en Sensor
(O2S
) control, checkin
g (before three wa
y catal
ytic converter
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.24.11

24-48

- Press buttons -0-, -0- and -5- to input display
group number 005 for bank 1, or press buttons -
0-, -0- and -6- to input display group number 006
for bank 2.

- Press -Q- button to confirm input.Read measuring value block 5 -4.6% 0.7% 0 % 0 %

Indicated on display (example)
Note:
If necessary, display group 005 (bank 1) or 006 (bank 2) for
troubleshooting can be read using "Basic Setting" function 04 and then
printed out page 01
-150
, Basic Setting. By selecting this function
(among other things) the evaporative emissions factor is not included.
Pa
ge 7 of 7 Ox
yg
en Sensor
(O2S
) control, checkin
g (before three wa
y catal
ytic converter
)
11/22/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU01.24.11