Heated Oxygen Sensors G39 and G108, Checking

Heated Oxygen Sensors G39 and G108, Checking

The following procedure is used to diagnose both Heated Oxygen Sensor (HO2S) (G39) and Heated Oxygen Sensor (HO2S) 2 (G108)

• Use only gold-plated terminals when servicing terminals in the electrical harness connectors of the Heated Oxygen Sensor (HO2S) (G39) and Heated Oxygen Sensor (HO2S) 2 (G108).

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• The Heated Oxygen Sensor (HO2S) (G39) and Oxygen Sensor (O2S) 2 Heater (Z28) fuses OK.

• The Oxygen Sensor (O2S) Heater (Z19) and Oxygen Sensor (O2S) 2 Heater (Z28) before catalytic converter OK.

• Battery voltage at least 12.5 volts.

• All electrical consumers such as, lights and rear window defroster, switched off.

• A/C switched off.

• Ground (GND) connections between engine/transmission/chassis OK.

• Exhaust system between catalytic converter and cylinder head properly sealed.

• Coolant Temperature at least 80° C.

Test procedure

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check

Start diagnosis

Function test

- Connect scan tool.

- Start the engine and let it run at idle.

- Select "Diagnostic mode 6: Check test results of components that are not continuously monitored".

- Select "Test-ID 01: Oxygen sensor monitoring before catalytic converter".

- Select "Test-ID 131: Dynamic test".

- Check the specified values at idle.






If specified values are obtained:

- End diagnosis and switch the ignition off.

If the specified values are not obtained:

Checking primary voltage

- Disconnect the black Heated Oxygen Sensor (HO2S) (G39) electrical harness connector - 1 - or the Heated Oxygen Sensor (HO2S) 2 (G108).





- Using a multimeter, check the Heated Oxygen Sensor (HO2S) electrical harness connector - 1 - terminals 1 to 5 for voltage.





Specified value: 0.400 to 0.500 Volts

- Switch the ignition off.

If the specified value was not obtained:

- Replace the Heated Oxygen Sensor (HO2S) (G39) or the Heated Oxygen Sensor (HO2S) 2 (G108).

If the specified value was obtained:

Checking wiring

If the manufacturers test box is being used. Perform the following step.

- Install the Test Box 105 Pin (VAG1598/31).

If the manufacturers test box is not being used. Perform the following step.

- Remove the Engine Control Module (ECM) (J623). Refer to => [ Engine Control Module J623, Replacing ] Engine Control Module J623, Replacing.

- Using a Multimeter, check the Heated Oxygen Sensor (HO2S) (G39) or the Heated Oxygen Sensor (HO2S) 2 (G108) electrical harness connector terminals to the Engine Control Module (ECM) (J623) electrical harness connector T121 terminals for an open circuit.















Specified value: 1.5 ohms Max.

If the specification was not obtained:

- Check the wiring for a short circuit to each other, Battery (+), and Ground (GND).

- Check the electrical harness connector for damage, corrosion, lose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:

- Erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory

- Perform a road test to verify repair.

If the DTC does not return:

Repair complete, Generate readiness code. Refer to => [ Readiness Code Description ] Readiness Code Description.

- End diagnosis.

If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:

- Replace the Engine Control Module (ECM) (J623). Refer to => [ Engine Control Module J623, Replacing ] Engine Control Module J623, Replacing.

- Assembly is performed in the reverse of the removal.

Final procedures

After repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.

End of diagnosis