1998 AUDI A8 sensor

24-116


Oxygen sensor heating for oxygen
sensors before and behind catalytic
converter, checking

Special Tools and Equipment

VAG1526A
VAG1594A
VAG1598/31
VAG1788/10 RPM adjuster
VAS5051 with VAG5051/1
- or
VAG1551 with VAG1551/3B
Pa
ge 49 of 63 Ox
yg
en sensor control, checkin
g
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU05.24.3

24-117

Note:
The heating circuit of the oxygen sensor is
monitored by On Board Diagnostic (OBD),
Check DTC memory Page 01
-15
.

- 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:
- Press buttons -0- and -8- to select "Read Measuring Value Block" and
press -Q- button to confirm input.
Read Measurin
g Value Block
Q
Input displa
y group number XXX

When indicated on display:
- Press buttons -0-, -4- and -1- to select "display group number 041" and
press -Q- button to confirm input.
Read Measuring Value Block 41
1
2
3
4

When indicated on display:
Note:
Increasing engine speed accelerates the obtaining of specified values. - Check specified values in display fields 1 and 3.
Pa
ge 50 of 63 Ox
yg
en sensor control, checkin
g
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU05.24.3

24-118


Display fields

1 2 3 4
Display group 041: Oxygen sensor heating (bank 1) at idle
Display
xxx kOhm ---
xxx kOhm ---
Indicated
Bank 1, sensor 1 Condition of heating
Bank 2, sensor 1 Condition of heating
Functional range Htng. bef. cat. ON
Htng. bef. cat. OFF Htng. beh. cat. ON
Htng. beh. cat. OFF
Specified value
0 to 0.9 kOhm Htng. bef. cat. ON/OFF
0 to 0.9 kOhm Htng. beh. cat. ON/OFF Important notes to display fields 1, 2, 3 and 4:

If oxygen sensors have not yet reached their operating temperature, there will be no indication in display fields 1 and 3,
i.e. they will both be empty. (increase engine speed to obtain specified values).
After reaching operating temperature of the two oxygen sensors, a resistance of less than 0.9 kOhm must be indicated in
display fields 1 and 3.
Do not continue test until a resistance of less than 0.9 kOhm is indicated in display fields 1 and 3.
At certain points of operation, the ECM "pulses" oxygen sensor heating. This means that oxygen sensor heating is
switched on and off at these points. It is entirely possible that the specified value "Htng. bef. Cat. OFF" or "Htng. beh. Cat.
OFF" will appear in display fields 2 and 4

- Press -C- button.
Pa
ge 51 of 63 Ox
yg
en sensor control, checkin
g
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU05.24.3

Read Measurin
g Value Block
Q
Input display group number XXX

When indicated on display:
- Press buttons -0-, -4- and -2- to select "display group number 042" and press -Q-
button to confirm input.
Pa
ge 52 of 63 Ox
yg
en sensor control, checkin
g
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU05.24.3

24-119

Read Measuring Value Block 42
1
2
3
4

When indicated on display:
- Check specified values in display fields 1 and 3.

Display fields

1 2 3 4
Display group 042: Oxygen sensor heating (bank 2) at idle
Display
xxx kOhm ---
xxx kOhm ---
Indicated
Bank 2, sensor 1 Condition of heating
Bank 2, sensor 2 Condition of heating
Functional range Htng. bef. cat. ON
Htng. bef. cat. OFF Htng. beh. cat. ON
Htng. beh. cat. OFF
Specified value
0 to 0.9 kOhm Htng. bef. cat. ON/OFF
0 to 0.9 kOhm Htng. beh. cat. ON/OFF Important notes to display fields 1, 2, 3 and 4:

If oxygen sensors have not yet reached their operating temperature, there will be no indication in display fields 1 and 3,
i.e. they will both be empty. (increase engine speed to obtain specified values).
After reaching operating temperature of the two oxygen sensors, a resistance of less than 0.9 kOhm must be indicated in
display fields 1 and 3.
Do not continue test until a resistance of less than 0.9 kOhm is indicated in display fields 1 and 3.
At certain points of operation, the ECM "pulses" oxygen sensor heating. This means that oxygen sensor heating is
switched on and off at these points. It is entirely possible that the specified value "Htng. bef. Cat. OFF" or "Htng. beh. Cat.
Pa
ge 53 of 63 Ox
yg
en sensor control, checkin
g
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU05.24.3

OFF" will appear in display fields 2 and 4
Pa
ge 54 of 63 Ox
yg
en sensor control, checkin
g
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU05.24.3

24-120
If specified value is not obtained:

- Check voltage supply of oxygen sensor heating
Page 24
-121
.

- Check oxygen sensor signal wire and activation
Page 24
-112
or Page 24
-114
.
Pa
ge 55 of 63 Ox
yg
en sensor control, checkin
g
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU05.24.3

24-121

Checking voltage supply for oxygen sensor
heating

Test requirement:

Fuse for oxygen sensor heating OK

Electrical Wiring Diagrams, Troubleshooting &
Component Locations binder

Fuel Pump (FP) OK, checking Page 24
-
49
.
Component location of harness connectors
Overview of component locations, page Page
24
-5

- Disconnect 4-pin harness connector leading to
respective oxygen sensor.

- Connect multimeter between terminal 1 and 2 for voltage
measurement.
Pa
ge 56 of 63 Ox
yg
en sensor control, checkin
g
11/23/2002 htt
p://127.0.0.1:8080/audi/servlet/Dis
play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU05.24.3