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Oxygen Sensor / Control After Converter, Checking



Oxygen Sensor And Oxygen Sensor Control After Three Way Catalytic (TWC) Converter, Checking

Special tools and equipment
- VAG 1551 Scan Tool or VAG 1552 with cable VAG 1551/3
- Test box VAG 1598/22
- Hand multimeter VAG 1526 or multimeter VAG 1715
- Adapter set VAG 1594
- Wiring diagram







- VAG 1788/10 Engine speed adjuster

Check conditions
- Exhaust system between catalytic converter and cylinder head must be free of leaks
- Coolant temperature must be at least 80 degree C, display group 04, display zone 3.

Functional check
- Connect VAG 1551 Scan Tool ((VAG 1552). Start engine and select "Address word" 01 of engine control module. When doing this engine must be running at idle speed. (Connecting scan tool and selecting engine control module [1][2][3]Connecting VAG Scan Tool 1551/1552).

Indicated on display

Rapid data transfer HELP
Select function XX

- Press keys 0 and 8 for function "Read Measuring Value Block" and confirm entry with Q key.

Indicated on display

Read Measuring Value Block
Input display group number XXX

- Press keys 0, 3 and 4 for "Display group number 34" and confirm entry with Q key.

Indicated on display: (1 to 4 = Display zones)

Read Measuring Value Block 34 ->
1 2 3 4

- Set an engine speed of 2200 to 2800 RPM with speed regulator VAG 1788/10:
- Maintain engine speed at 2200 to 2800 RPM until catalytic converter temperature in display zone 2 exceeds 352 degree C.

NOTE: This process can take a few minutes.

- Press C key.

Indicated on display

Read Measuring Value Block
Input display group number XXX

- Press keys 0, 3 and 0 for "Display group number 30" and confirm entry with Q key.

Indicated on display: (1 to 4 = Display zones)

Read Measuring Value Block 30 ->
1 2 3 4

- Check the operating condition of the Oxygen sensor control after catalytic converter (display zone 2):
Specification: 111

NOTE: The bits in display zone 2 will not be set to 1 until the catalytic converter temperature has risen to above 352 degree C ( display group 34, display zone 2).

Significance of 3 digit number block in display zone 2:







Change to display group 37 as follows:
- Press C key.
- Press keys 0, 3 and 7 for "Display group number 37" and confirm entry with Q key.

Indicated on display: (1 to 4 = Display zones)

Read Measuring Value Block 37 ->
1 2 3 4

- Check dwell period of Oxygen sensor control before catalytic converter in display zone 3:
Specification: 0 to 200 ms
- Check result of diagnosis in display zone 4:
Specification: B1-P2 OK

NOTE: The Oxygen sensor control after catalytic converter is master of the Oxygen sensor control before catalytic converter and serves as a corrective regulation.







It corrects slight movements of the mixture (e.g. towards rich) by the Oxygen sensor before catalytic converter in that it holds the Oxygen sensor control at the upper or lower point for a certain period (dwell period). If the period is in the positive range (e.g. 50 ms), the mixture is moved towards rich. If the period is in the negative range (e.g. -50 ms) the mixture is moved towards lean.
- Check Oxygen sensor voltage in display zone 2:
Specification: 0 to 1 V (can fluctuate slightly)

If the display in display zone 2 remains constantly at a value:
- Continue check according to following table.







If B1-P2 OK appears in display zone 4 and the value displayed in display zone 3 is above 200 ms:
- Check exhaust system for leaks.

If B1-P2 n.OK appears in display zone 4 and the value displayed in display zone 3 is above 1200 ms:
- Press -> key.
- Press keys 0 and 6 for function "End Output" and confirm entry with Q key.
- Switch ignition off.
- Carry out a test drive to remove possible residue on Oxygen sensor and repeat check.

Observe the valid safety precautions when carrying out a road test Technician Safety Information.

If the specifications are again not attained:
- Replace Oxygen Sensor (O2S) behind three way catalytic converter (TWC) -G130-.

NOTE: If the Oxygen sensor voltage is OK and the delay period for the Oxygen sensor control after catalytic converter is still above 1200 ms even after a test drive, this points to an aged Oxygen sensor before catalytic converter.

Checking basic voltage







- Remove protective cover -arrows- and separate 4-pin connector (brown) to Oxygen Sensor (O2S) behind three way catalytic converter (TWC) -G130-.







- Connect multimeter with auxiliary cables from VAG 1594 to measure voltage at contacts 3 + 4 (connector to Motronic control module).
- Start engine and measure the basic voltage.
Specification: 0.40 to 0.50 V
- Switch ignition off.

If the specification is not obtained:
- Check Oxygen sensor wiring

If the specification is obtained:
- Replace Oxygen sensor 2 -G130-.

Checking Oxygen sensor wiring, Oxygen sensor 2






- Connect test box VAG 1598/22 to control module wiring harness.







- Check wiring for open circuit between test box and 4 pin connector to Motronic control module using wiring diagram.
Contact 3 + socket 51
Contact 4 + socket 52
Wire resistance: Max. 1.5 Ohm
- Additionally check wiring at 4 pin connector for short to one another.
Contact 4+socket 51, specification: Infinite Ohm

If no wiring malfunction is detected:
- Replace engine control module.
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