Heated Oxygen Sensor Heater Circuit, Checking

Heated Oxygen Sensor Heater Circuit, Checking

• When servicing electrical harness connector terminals for the Heated Oxygen Sensor (HO2S) (G39), use only gold-plated terminals.

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• The Fuse (S17) OK.

• Battery voltage at least 12.5 volts.

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

• Vehicles with automatic transmission, shift selector lever into position "P" or "N".

• A/C switched off.

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

• Ignition switched off.

Test procedure

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

Start diagnosis

- Remove the engine cover with air filter.

Checking internal resistance





- Disconnect the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector - 2 -.

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) terminals 3 to 4 for resistance.

Specified value: 2.5 to 10.0 ohms (at approx. 20° C)

If the specification was not obtained:

- Replace the Heated Oxygen Sensor (HO2S) (G39).

If the specification was obtained:

Checking voltage supply

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector terminal 3 to Ground (GND) for voltage.









Specified value: Battery voltage.

If the specification was not obtained:

- Check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector terminal 3 to theEngine Component Power Supply Relay (J757) terminal 87 for an open circuit, or a short circuit to Ground (GND).

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

- If necessary, repair the faulty wiring connection.

If the specification was obtained:

Checking Ground (GND) activation

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

- Install the test box.

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 ] Engine Control Module, Replacing.

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T94 for resistance.





Specified value: 1.5 ohms max.

If the specification was not obtained:

- Check the wiring for an open circuit, short circuit to each other, Battery (+), or Ground (GND).

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

- If necessary, repair the faulty wiring connection.

If no malfunction is detected in the wiring and if the voltage supply was OK:

- 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 ] Monitors, Trips, Drive Cycles and Readiness Codes.

- End diagnosis.

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

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

- Assembly is performed in the reverse of the removal.

Final procedures

After repair work, the following work steps must be performed in the mentioned 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.