Sensor and Control Check

Heated Oxygen Sensor (HO2S) And Oxygen Sensor Control After Three Way Catalytic Converter (TWC), Checking

NOTE: The oxygen sensor before catalytic converter (bank 1, sensor 1) regulates to Lambda 1. If this oxygen sensor is damaged, e.g. due to soiling or overheating, the regulation value may have shifted. Deviations from Lambda 1 are detected by the oxygen sensor after catalytic converter (bank 1, sensor 2). If it recognizes the deviations downward or upward, it influences the regulation before catalytic converter, generally increasing or decreasing it respectively.

Special Tools and Equipment

- VAG1526A
- VAG1594A
- VAG1598/31
- VAG1788/10 RPM adjuster
- VAS5051 with VAG5051/1

Test requirements:
- Exhaust system free of leaks.
- Coolant Temperature at least 80 °C.

Test sequence
- Connect VAS5051 tester and select vehicle system "01 - Engine electronics". Engine must run at idle for this.

- Install VAG1788/10 RPM adjuster on the accelerator pedal and raise the engine speed to 2600 RPM.

Test requirement:
- Engine running at 2600 RPM.

Display on VAS5051:
- In selection -1-, click on the diagnostic function "04 - Basic setting".

Display on VAS5051:
1 - Enter display group Max. input value = 255
- Select function "030" in button field -2- for "display group number 030" and press Q button to confirm input.

Display on VAS5051:
- Check specified value in display field -2-.

NOTE: "Oxygen sensor status" indicates status of oxygen sensor control and oxygen sensors.

Display Group 030:

Significance Of 3 Digit Indications In Display Group 030:

Display on VAS5051:
- Do not continue test until indication in display field -2- has reached "110" at least once.

Checking oxygen sensor control after catalytic converter

Test requirement:
- Engine continues to run at 2600 RPM.
- Click on <- button

Display on VAS5051:
1 - Enter display group Max. input value = 255
- Select function "037" in button field -2- for "display group number 037" and press -Q- button to confirm input.

Display on VAS5051:
- Check oxygen sensor voltage in display field -2-.
- Check oxygen sensor correction value in display field -3- and diagnostic result in display field -4-.

Display Group 037:

Evaluation display group 037

Evaluation Display Group 037:

Continuation
If specified value in display field 3 and 4 is not obtained:
- Road test vehicle in order to free oxygen sensor of possible residue and repeat test.

If specified value in display field 3 and 4 is not obtained, even after road test:
- Replace Heated Oxygen Sensor (HO2S) -G39-.

NOTE: If oxygen sensor voltage is OK and oxygen sensor correction value is still above 0.02 ms, even after a road test, this suggests aging of an oxygen sensor before catalytic converter.

Checking primary voltage

- Disconnect 4-pin harness connector -1- (brown) to Oxygen Sensor (O2S) behind Three Way Catalytic Converter (TWC) -G130-.

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.

- Connect multimeter between terminal 3 and 4 for voltage measurement.
- Switch ignition on.
- Specification: 0.400 to 0.500 V
- Switch ignition off.

If specified value is not obtained:
- Check oxygen sensor wiring.

If specified value is obtained:
- Replace Oxygen Sensor (O2S) behind Three Way Catalytic Converter (TWC) -G130-.

Checking oxygen sensor wires

- Check the following wire connections for open circuit.

Harness connector VAG1598/31 test box
Terminal Socket

3 68
4 69

- Repair open circuit if necessary
- Check wires to each other for short circuit

If wire connection is OK:
- Replace Engine Control Module (ECM)