AUDI A4 1999 B5 / 1.G APB Engine Oxygen Sensor Control Checking Service Manual

24-113

Continuation
If the specified value in display group 037 and
038, display 3 or 4 is not obtained:

- Check exhaust system and catalytic converter
for leaks (check clamps and exhaust for
damage)

- If the difference of the values in measuring
blocks, display fields 3 (oxygen sensor
correction value) is to large (e.g.:+500 ms, -500
ms), it is possible that the oxygen sensor are
interchanged (mixed up).
If none of the causes are identified:

- Replace particular oxygen sensor "before"
catalytic converter.
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24-114

Oxygen sensor heater for oxygen
sensor, checking


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

- 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
- Press buttons -0- and -8- to select function "Read Measuring Value
Block" and confirm entry with -Q- button.
Read Measurin
g Value Block
Input display group number XXX

Indicated on display
- Press buttons -0-, -4- and -1- to select "display group number 041" and
confirm entry with -Q- button.
Read Measuring Value Block 41
1
2
3
4

Indicated on display
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24-115

- Adjust engine speed to approx: 3000 RPM

- Check resistance of oxygen sensor heater.

Display fields

1 2 3 4
Display Group 041: Oxygen sensor heater, Bank 1 (at idle speed)
Display
xxx kOhm
Htg.bC.ON
xxx kOhm
Htg.aC.ON
Indicates
Bank 1, Sensor 1
Status of
heater Bank 1, Sensor 2
Status of
heater
Range
Htg.bC.ON
Htg.bC.OFF
Htg.aC.ON
Htg.aC.OFF
Specified
value 0 - 0.5 kOhm
Htg.bC.ON/OFF
0 - 0.5 kOhm
Htg.aC.ON/OFF
Note
It can take a few minutes until
specification are obtained
It can take a few minutes until
specified values are obtained
- Press -C- button.

- Press buttons -0-, -4- and -2- to select "display
group number 042" and confirm entry with -Q-
button.
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24-116


Display fields

1 2 3 4
Display Group 042: Oxygen sensor heater, Bank 2 (at idle speed)
Display
xxx kOhm
Htg.bC.ON
xxx kOhm
Htg.aC.ON
Indicates
Bank 2, Sensor 1
Status of
heater Bank 2, Sensor 2
Status of
heater
Range
Htg.bC.ON
Htg.bC.OFF
Htg.aC.ON
Htg.aC.OFF
Specified
value 0 - 0.5 kOhm
Htg.bC.ON/OFF
0 - 0.5 kOhm
Htg.aC.ON/OFF
Note
It can take a few minutes until
specifications are obtained
It can take a few minutes until
specifications are obtained If the specification is not attained:

- Check voltage supply for oxygen sensor heater
Page 24
-117
.

- Check oxygen sensor signal wire and activation
Page 24
-122
.
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24-117

Checking voltage supply for oxygen sensor
heater
Component location of 4-pin harness connector
of oxygen sensors Page 24
-5 .

- Check fuse for oxygen sensor heater

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
- Disconnect 4-pin harness connector of particular
oxygen sensor.

If there is no voltage reading: - Connect hand-held multimeter (voltage measurement range) between
sockets 1 (B+) and 2 (Ground (GND)) using test leads from VAG1594
connector test kit.
- Operate starter briefly.
Specified value: approx. battery voltage
- Connect hand-held multimeter (voltage measurement range) between
socket 1 (B+) and vehicle Ground (GND) using test leads from
VAG1594 connector test kit.
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24-118

- Operate starter briefly.

Specified value: approx. battery voltage
If there is still no voltage reading:

- Check for open circuit and/or short circuit in
wiring between fuel pump relay and socket 1 on
the relevant oxygen sensor connector (on wiring
harness) via fuse.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations If the voltage supply is OK:

- Connect hand-held multimeter (voltage measurement range) between
socket 2 (switched Ground (GND) connection from engine control
module) and B+ terminal using test leads from VAG1594 connector test
kit.
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24-119

- Start engine.

Specified value: approx. battery voltage
(fluctuating)

Note:
At certain points in the operating range the
engine control module continuously "switches"
the Ground (GND) connection to the oxygen
sensor heater. That means, it repeatedly
connects and disconnects the Ground (GND)
connection at these points. For this reason the
voltage reading on the tester may fluctuate.

- Switch ignition off.
If there is no voltage reading:

- Connect VAG1598/31 test box to wiring harness
for engine control module. Do not connect to the
engine control module itself Page 24
-20
.

- Check for open circuits in the following wiring connection:
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24-120

Heated Oxygen Sensor (HO2S) -G39
Connector on wiring
harness, socket
VAG1598/31 test
box, socket
2 5 (Ground)
Heated Oxygen Sensor (HO2S) 2 -G108
Connector on wiring
harness, socket
VAG1598/31 test
box, socket
2 4 (Ground)
Oxygen Sensor (O2S) Behind Three Way
Catalytic Converter (TWC) -G130
Connector on wiring
harness, socket
VAG1598/31 test
box, socket
2 63 (Ground)
Oxygen Sensor (O2S) 2 Behind Three Way
Catalytic Converter (TWC) -G131
Connector on wiring
harness, socket
VAG1598/31 test
box, socket
2 6 (Ground)
Resistance in wiring: max. 1.5 Ohm

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
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24-121
If the wiring is OK but the oxygen sensor heater
still has no Ground (GND) connection:

- Replace particular oxygen sensor.

- Display readiness code Page 01
-101
. The
readiness code must be generated if the DTC
memory was erased Page 01
-105
.
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24-122

Oxygen sensor signal wire and
activation, checking


Note:
The oxygen sensor signal is monitored by the
OBD system.

- Check DTC memory Page 01
-15
.

- If a oxygen sensor malfunction is displayed and
the oxygen sensor heater is OK, disconnect
harness connector for relevant oxygen sensor.
Component location of 4-pin harness connector
of oxygen sensor Page 24
-5 .

If the Specified value is not obtained, check oxygen sensor wiring: - Test voltage by connecting hand-held multimeter Fluke 83 (or
equivalent) (measuring range 2 V) between sockets 3 and 4 of
connector on wiring harness.
-
Switch ignition on. Specified value: 450 50 mV. Bank 1, Sensor 1 Page 24
-123
.
Bank 1, Sensor 2 Page 24
-125
.
Bank 2, Sensor 1 Page 24
-127
.
Bank 2, Sensor 2 Page 24
-129
.
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