1996 AUDI A6 ATW Engine Oxygen Sensor Control Workshop Manual

24-87

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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Special tools and equipment

VAG1526A
VAG1594A
VAG1598/31
VAG1788/10 RPM adjuster
VAS5051 with VAG5051/1
- or
VAG1551 with VAG1551/3A
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24-89

Test requirements:

Road test performed and DTC memory
erased.
Coolant Temperature at least 80 C.

Test sequence

- Connect VAS5051 tester or VAG1551 scan tool
and select control module for engine electronics
using "address word" 01 Page 01
-10
. Engine
must run at idle.
Rapid data transfer
HELP
Select function XX

When indicated on display
Note:
During basic setting, the Evaporative Emission (EVAP) canister purge
regulator valve (EVAP valve -N80-) is closed and the A/C compressor is
switched off - Press buttons -0- and -4- to select "Initiate basic setting" and press -Q-
button to confirm input.
Basic Settin
g
Q
Enter displa
y group number XXX

When indicated on display
- Press buttons -0-, -3- and -4- to select "display group number 034" and
press -Q- button to confirm input.
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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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Display fields

1 2 3 4
Display group 037: Diagnostic oxygen sensor control system
Display xxx %
x.xxx volts
xxx ms
---
Indicated Engine
load Oxygen sensor voltage
Bank 2, sensor 1 Dwell time, oxygen sensor control
before catalytic converter, bank 1 Diagnostic condition
Functional
range


Test OFF
Test ON
System OK
System not OK
Specified
value 15 to 33
% 0.100 to 0.900 V
-150 to 150 ms System OK
Note

If specified value is not
obtained: Evaluation display
field 2 Page 24
-94

If value climbs to above 300 ms,
this indicates a leaking exhaust
system or faulty oxygen sensor If "SYST not OK" is
displayed: Check DTC
memory Page 01
-16

Note for display field 3:
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. toward rich or lean) due to 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 this time is in the
negative range (i.e. -50 ms), mixture is shifted in the -lean- direction.
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Evaluation display group 037 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
-96


Open circuit in wire 3 between oxygen sensor
and control module
larger than
1.100 V Short circuit to B+ in wire 4 between oxygen
sensor and control module - Check oxygen sensor wiring, oxygen sensor
behind catalytic converter Page 24
-97

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