Heated Oxygen Sensors and Sensor Regulation Before Catalytic Converter, Checking

Heated Oxygen Sensors and Sensor Regulation before Catalytic Converter, 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) Engine Electronics Fuse (S282) OK.

• The Oxygen Sensor (O2S) Heater (Z19) and Oxygen Sensor (O2S) 2 Heater (Z28) before catalytic converter OK. Refer to => [ Oxygen Sensors before Catalytic Converter, Checking Heater ] Oxygen Sensors Before Catalytic Converter, Checking Heater.

• The Fuel Pump (FP) Relay (J17) 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.

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:

Procedure for accessing the Heated Oxygen Sensor (HO2S) 2 (G108) electrical harness.

- Remove the left side engine compartment cover - 1 -.





- Remove the coolant expansion tank screw - arrow -.

- Disconnect the electrical connector from the Engine Coolant Level (ECL) Warning Switch (F66) and set aside coolant reservoir with coolant hoses - 1 -and - 2 - connected.





- Disconnect the Heated Oxygen Sensor (HO2S) 2 ( G108) electrical harness connector - 4 -.





Procedure for accessing the Heated Oxygen Sensor (HO2S) (G39) electrical harness.

- Remove the cover on the right side of the engine compartment - 1 -.





- Remove the air intake duct - arrows -.





- Disconnect the Heated Oxygen Sensor (HO2S) (G39 ) electrical harness connector - 1 -.





Checking primary voltage

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) electrical harness connector 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) Refer to Fuel Injection and Ignition Repair Information.

If the specified value was obtained:

Checking wiring

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

- Install the test box. Refer to Fuel Injection and Ignition Repair Information.

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

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

- Using a Multimeter, check the Heated Oxygen Sensor (HO2S) (G39) or the Heated Oxygen Sensor (HO2S) 2 (G108) electrical harness connector terminals to the Motronic 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:

- Replace the Motronic Engine Control Module (ECM) (J623).

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.