Oxygen Sensor Control/O2S After TWC -G130- and -G131-, Check

Oxygen Sensor Control / Oxygen Sensor (O2S) Behind Three Way Catalytic Converter (TWC) -G130- And O2S 2 Behind TWC -G131-, Checking

Special tools and equipment required

- V.A.G 1526 A
- V.A.G 1594 A
- V.A.G 1598/31
- V.A.G 1788/10
- VAS 5051 with VAS 5051/1
or
- V.A.G 1551 with V.A.G 1551/3 A

NOTE: The oxygen sensor upstream of the catalytic converter (bank 1, sensor 1 or bank 2, sensor 1) effects regulation to lambda = 1. Contamination or overheating of this oxygen sensor for example may produce a shift in the control value. Any deviations from lambda = 1 are detected by the oxygen sensor downstream of the catalytic converter (bank 1, sensor 2 or bank 2, sensor 2). On recognizing downward or upward deviations, it correspondingly influences control action upstream of the catalytic converter, so as to produce an appropriate increase or reduction.

Requirements
- No leaks in exhaust system
- Coolant temperature at least 80 degree C see Display group 004, display zone 3
- Engine idling
- Aging of oxygen sensors upstream of catalytic converter checked.

Work sequence
- Connect vehicle diagnostic, testing and information system VAS 5051 and select vehicle system "01 - Engine electronics" from list. Engine must be idling. Connecting VAS 5051 Scan Tool

Indicated on VAS 5051:

- From list -1- select diagnostic function "04 - Basic setting".

Indicated on VAS 5051:

1 Enter display group
- Use keypad -2- to enter "030" for "Display group number 030" and confirm by touching Q key.

Indicated on VAS 5051:

- Activate basic setting by touching key -A-.
- Check display in zones -2- and -4-.

NOTE:
- Specifications are obtained faster by increasing engine speed.
- "Oxygen sensor status" indicates status of oxygen sensor control and oxygen sensors.

Display Zone 030:

NOTE:
- Only the last three positions on the right in the five-position display (in zones 1 and 3) or the four-position display (in zones 2 and 4) are relevant.
- Control function of oxygen sensor downstream of catalytic converter (bank 1, sensor 2 and bank 2, sensor 2) is not active if there is no engine load.
- First position in 3-position display (heating) fluctuates between 0 and 1.
- Third position in 3-position display (lambda control) fluctuates between 0 and 1.

Explanatory notes on 3-position display in display group 30

NOTE: Only the last three positions on the right in the five-position display (in zones 1 and 3) or the four-position display (in zones 2 and 4) are relevant.

Indicated on VAS 5051:

- Do not continue with test until display in zones -2- and -4- has reached "110" at least once.
- Touch <- key.

Checking oxygen sensor control downstream of catalytic converter

Indicated on VAS 5051:

1 Enter display group
- Use keypad -2- to enter "037" for "Display group number 037" and confirm by touching Q key.

Indicated on VAS 5051:

- Activate basic setting by touching key -A-.
- Check dwell time between oxygen sensor 1 upstream of catalytic converter and oxygen sensor 2 downstream of catalytic converter in display zone 3 and diagnostic result in display zone 4.

Diplay Group 037:

Note on display zone 3:
Oxygen sensor control downstream of catalytic converter is higher-ranking than oxygen sensor control upstream of catalytic converter and acts as setpoint control. It corrects minor oxygen sensor upstream of catalytic converter shifts to rich or lean by holding oxygen sensor control upstream of catalytic converter on upper/lower stop for a certain period (dwell time). If the time is in the positive range (e.g. 50 ms) the mixture is enriched. If the time is in the negative range (e.g. -50 ms) the mixture is leaned.

- Touch <- key.

Indicated on VAS 5051:

1 Enter display group
- Use keypad -2- to enter "038" for "Display group number 38" and confirm by touching Q key.

Indicated on VAS 5051:

Display Group 038:

Note on display zone 3:
oxygen sensor control downstream of catalytic converter is higher-ranking than oxygen sensor control upstream of catalytic converter and acts as setpoint control. It corrects minor oxygen sensor upstream of catalytic converter shifts to rich or lean by holding oxygen sensor control upstream of catalytic converter on upper/lower stop for a certain period (dwell time). If the time is in the positive range (e.g. 50 ms) the mixture is enriched. If the time is in the negative range (e.g. -50 ms) the mixture is leaned.

(Continuation)
If reading does not match specification in display zones 3 or 4:
- Locate leakage air at exhaust or catalytic converter (check screw-type clamps and exhaust for damage).
- Replace relevant oxygen sensor "upstream of" catalytic converter.