Oxygen Sensor / Control Before Converter, Checking

Oxygen Sensor And Oxygen Sensor Control Before 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

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

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 HELP
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 Oxygen sensor control status before catalytic converter (display zone 1):
Specification: 1 1 1

If the specification is not obtained:
- Check Heated Oxygen Sensor (HO2S) before catalytic converter. Heated Oxygen Sensor (HO2S) -G39- Before Converter, Checking

Significance of 3 digit number block in display zone 1:







If the specification is obtained:
- Change to display group 32 as follows:
- Press C key.
- Press keys 0, 3 and 2 for "Display group number 32" and confirm entry with Q key.

Indicated on display: (1 to 4 Display zones)

Read Measuring Value Block 32 ->
1 2 3 4

- Check Oxygen sensor learned values at idle speed (additive) in display zone 1.
Specification: -10.0 to 10.0%
- Check Oxygen sensor learned values at part load (multiplicative) in display zone 2.
Specification: -10.0 to 10.0%

If the specification is not obtained: Evaluating display group 32, Display Groups 30 to 46, 99 (Oxygen Sensor Control), Evaluation

If the specification is obtained:

- Change to display group 33 as follows:
VAG 1551: Press key 3
VAG 1552: Press key upper-arrow

Indicated on display: (1 to 4 Display zones)

Read Measuring Value Block 33 ->
1 2 3 4

- Observe Oxygen sensor control in display zone 1. Display must fluctuate at least 2% in the range -10.0 to 10.0%
- Check Oxygen sensor voltage in display zone 2. Voltage must fluctuate at least 20 times per minute in range of 0 to 1.0 V.

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







If the Oxygen sensor control in display zone 1 does not fluctuate as stated:

- Press -> key.
- Press keys 0 and 6 for "End data transfer" function and confirm input with Q key.
- Carry out road test to burn Oxygen sensors clean and repeat check.

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

If the specifications in display zone 1 are not obtained even after a test drive, or the value does not fluctuate by at least 2%:
- Check Oxygen sensor before catalytic converter for aging Oxygen Sensor 1 Aging, Checking

Checking basic voltage







- Remove protective cover -arrows- and separate 4 pin connector (black) to heated oxygen sensor (HO2S) before catalytic converter -G39-.







- Connect multimeter with auxiliary cables from VAG 1594 to measure voltage at contacts 3+4 (connector to engine control module).
- Switch ignition on and measure 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 heated oxygen sensor (HO2S) before catalytic converter -G39-.

Checking Oxygen sensor wiring







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







- Check wiring between test box and 4 pin connector (to control module) for open circuit according to wiring diagram.
Contact 3 + socket 25
Contact 4 + socket 26
Wire resistance: Max. 1.5 Ohm
- Check wiring at connector contacts 3+4 for short circuit to contacts 1+2 using wiring diagram.
Specification: Infinite Ohm

If no wiring malfunction is detected:
- Replace heated oxygen sensor (HO2S) before catalytic converter -G39-.