catalytic converter AUDI A3 1998 8L / 1.G ATW Engine Oxygen Sensor Control Workshop Manual

24-71


Oxygen sensor control,
checking Oxygen sensor and oxygen sensor control
before catalytic converter, checking

Special tools and equipment

VAG1526A
VAG1594A
VAG1598/31
VAS5051 with VAG5051/1
- or
VAG1551 with VAG1551/3A
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Continuation
If specified value in display field 1 is not obtained
or if value does not fluctuate at least 2 %:

- Road test vehicle in order to free oxygen sensor
of possible residue and repeat test.
If specified value in display field 1 is not obtained
even after road test or if value does not fluctuate
at least 2 %:

- Check primary voltage Page 24
-80
.

- Check oxygen sensor heating Page 24
-99
.

- Check oxygen sensor before catalytic converter
for aging Page 24
-83
.
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24-80
Evaluation display group 033 Display field:
2
Possible cause
Corrective action
constant about
0.450 V
Open circuit in wire 4 between oxygen sensor
and control module - Check primary voltage Page 24
-80


Open circuit in wire 3 between oxygen sensor
and control module
constant about
0.200 V Oxygen sensor faulty- Replace oxygen sensor
larger than
1.100 V Short circuit to B+ in wire 4 between oxygen
sensor and control module - Check oxygen sensor wiring, oxygen sensor
before catalytic converter Page 24
-81

smaller than
0.150 V
Short circuit to Ground (GND) in wire 4 between
oxygen sensor and control module

Checking primary voltage

Note:
Coolant reservoir screws must be removed and coolant reservoir must be
placed to side in order to access the harness connector. The coolant hoses
can remain connected. - Disconnect 4-pin harness connector -2- (black) to Heated Oxygen Sensor
(HO2S) -G39- before catalytic converter.
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If specified value is not obtained:
If specified value is obtained:
Checking oxygen sensor wires - Connect multimeter between terminal 3 and 4 for voltage
measurement.
- Switch ignition on.

Specification: 0.400 to 0.500 V
- Switch ignition off.
- Check oxygen sensor wiring.
- Replace Heated Oxygen Sensor (HO2S) -G39-.

Note:
Coolant reservoir screws must be removed and coolant reservoir must be
placed to side in order to access the harness connector. The coolant
hoses can remain connected. - Disconnect 4-pin harness connector -2- (black) to Heated Oxygen
Sensor (HO2S) -G39- before catalytic converter.
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24-83

Oxygen sensor aging (oxygen sensor
before catalytic converter), checking


Special tools and equipment

VAG1788/10 RPM adjuster

or
Test requirement:
VAS5051 with VAG5051/1VAG1551 with VAG1551/3ACoolant Temperature at least 80 C.
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Display fields

1 2 3 4
Display group 034: Diagnostic oxygen sensor aging
Display xxxx/min
xxx C
x.x s
---
Indicated Engine speed
(RPM) Exhaust
temperature Period duration Oxygen sensor before
Catalytic converter Diagnostic
condition
Functional
range

Test OFF
Test ON
B1-S2 OK
B1-S2 not OK
Specified
value 1800 to 2200
RPM more than 350 C
0.0 to 1.0 s B1-S2 OK
Note


If specified value is not obtained Continuation, Page 24
-
86

Note for display field 2:
Calculated value from engine speed and engine load.
Note for display fields 3 and 4:
Period duration is the time between two oxygen sensor voltage jumps (e.g. rich - lean - rich) and is therefore a measurement
of the aging condition of the oxygen sensor. If the specified time is exceeded, display field 4 will indicate = B1-S1 not OK.
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Heated Oxygen Sensor (HO2S) and
oxygen sensor control after Three Way
Catalytic Converter (TWC), checking


Note:
Oxygen sensor control behind catalytic converter
is superior to oxygen sensor control before
catalytic converter and is responsible for control
correction.

It corrects slight changes in the mixture (i.e. enrichment) via the oxygen
sensor before catalytic converter by holding oxygen sensor control before
catalytic converter at its higher or lower point for a specific time (dwell
time). If this time is in the positive range (i.e. 50 ms), mixture is shifted in
the -enrich- direction. If it is in the negative range (e.g. -50 ms), mixture
will be shifted in the -lean- direction.
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24-90

System in basic setting 34
1
2
3
4

When indicated on display
Note:
This process can take a few minutes. - Use VAG1788/10 RPM adjuster to adjust engine speed to between
2800 and 3200 RPM.
- Continue test as soon as display field 2 indicates an exhaust
temperature of more than 350 C. - Press -C- button.
- Use VAG1788/10 RPM adjuster to adjust engine speed to between
1800 and 2200 RPM.
Basic Setting
Q
Enter displa
y group number XXX

When indicated on display
- Press buttons -0-, -3- and -0- to select "display group number 030" and
press -Q- button to confirm input.
System in basic setting 30
1
2
3
4

When indicated on display
Note:
"Oxygen sensor status" indicates status of oxygen sensor control and
oxygen sensor. - Check oxygen sensor status for oxygen sensor behind catalytic
converter in display field 2.
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Display fields

1 2 3 4
Display group 030: Oxygen sensor status with engine at idle
Display X X X
X X X

Indicated Oxygen sensor status, bank 1, sensor 1
Oxygen sensor status Bank 2, sensor 1

Functional range 0 = off
1 = on 0 = off
1 = on

Specified value 1 1 1
1 1 0

Note
If specified value is not obtained Page 24
-99

Significance of 3 digit indications in display group 030 X
X
X
Display fields 1 and 2
X Oxygen sensor control: 0= not active; 1 = active
X Operational readiness of oxygen sensor: 0= not active; 1 = active
X Condition of oxygen sensor heater: 0= not active; 1 = active
Note:

Oxygen sensor control of oxygen sensor behind catalytic converter (B1-S2) is not active without engine load.
The first position of the 3 digit indication (heating) fluctuates between 0 and 1.
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Checking oxygen sensor control behind
catalytic converter

- Press -C- button.Basic Setting
Q
Enter displa
y group number XXX

When indicated on display
- Press buttons -0-, -3- and -7- to select "display group number 037" and
press -Q- button to confirm input.
System in basic setting 37
1
2
3
4

When indicated on display
- Check oxygen sensor voltage in display field 2.
- Check dwell time of oxygen sensor control before catalytic converter in
display field 3 and diagnostic result in display field 4.
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