Heated Oxygen Sensor 1, Checking

Heated Oxygen Sensor 1, Checking

The following procedure is used to diagnose Heated Oxygen Sensor (HO2S) (G39)

• When servicing electrical harness connector terminals for the Heated Oxygen Sensors, use only gold-plated terminals.

Special tools, testers and auxiliary items required

• multimeter

• Wiring diagram.

Test requirements

• The Heated Oxygen Sensor (HO2S) (G39) fuse 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

Checking internal resistance

- Disconnect the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector - 3 -.





- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) terminals 1 to 2 for resistance.

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

If the specification was not obtained:

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

If the specification was obtained:

Checking voltage supply

Switch the ignition on.

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector terminal 1 to the Fuel Pump (FP) Relay (J17) terminal 20/87 for voltage.









Specified value: Battery voltage.

Switch the ignition off.

If the specification was not obtained:

- Check the wiring for a short circuit to each other, Ground (GND), or an Open circuit.

- 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, Removing and Installing ] Engine Control Module, Removing and Installing.

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector to the Engine Control Module (ECM) (J623) electrical harness connector 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 (+), Ground (GND) or an Open circuit.

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

- If necessary, repair the faulty wiring connection.

- 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 ] Readiness Code.

- 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 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 ] Readiness Code.