O2 Sensor Heater Before Catalytic Converter

Heated Oxygen Sensor (HO2S) G39 before catalytic converter, heater circuit checking

Note:
When servicing terminals in harness connector of Heated Oxygen Sensor (HO2S) G39, 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.
- 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.
- 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. Service and Repair

Start diagnosis

- Remove the engine cover with air filter.

Checking internal resistance






Remove the protective cover - arrows - and disconnect the Heated Oxygen Sensor (HO2S) G39 electrical harness connector.






- Using a multimeter, check the Heated Oxygen Sensor (HO2S) G39 terminals 3+4 for an open circuit.

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 is 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 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 the specification was obtained:

Checking Ground (GND) activation

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

- Install the test box Test Box 105 Pin VAG1598/31.

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

- Remove the Motronic Engine Control Module (ECM) J220. Service and Repair






- Using a multimeter , check the Heated Oxygen Sensor (HO2S) G39 electrical harness connector terminal 4 to the Motronic Engine Control Module (ECM) J220 electrical harness connector T121 terminal 5 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 detected in the wiring and if the voltage supply was OK:

- Erase the DTC memory. Diagnostic Mode 4: Reset/Erase Diagnostic Data

- Perform a road test to verify repair.

- If the DTC does not return:

Repair complete, Generate 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 MFI Engine Control Module (ECM) J220. Service and Repair

- Assembly is performed in the reverse of the removal.

Final procedures

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

1. Check the DTC memory.
2. If necessary, erase the DTC memory.
3. If the DTC memory was erased, generate readiness code.

End diagnosis