Heated Oxygen Sensor G39, Checking

Heated Oxygen Sensor G39, Checking

Special tools, testers and auxiliary items required
- Multimeter.
- Wiring diagram.

Test requirements
- The Motronic Engine Control Module (ECM) Power Supply Relay 2 J670 OK.
- Fuse SB45 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.
- Ignition switched off.

Test procedure
- Perform a preliminary check to verify the customers complaint. Preliminary Check

Function test
- Perform the function test in Diagnostic Mode 06. Diagnostic Mode 06 - Read Test Results For Specific Diagnostic Functions

If the specified values are not obtained:

Start Diagnosis
- Remove the engine cover with air filter.

If the specified values are not obtained:

Checking primary voltage







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







- Using a multimeter, check the Heated Oxygen Sensor (HO2S) G39 terminals 1 to 5 for voltage.
- Crank the engine.

Specified value: 0.4 to 0.5 Volts

- Switch the ignition off.

If the specified value was not obtained:
- Replace the Heated Oxygen Sensor (HO2S) G39

If the specified value was obtained:

Checking wiring
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.







- Using a Multimeter, check the Heated Oxygen Sensor (HO2S) G39 electrical harness connector terminals to the Motronic Engine Control Module (ECM) J623 electrical harness connector T94 terminals for an open circuit.

Heated Oxygen Sensor (HO2S) Motronic Engine Control Module
G39 electrical harness (ECM) J623 electrical connector
connector terminals T94 terminals or test box sockets
1 60
2 61
5 81
6 82

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, loose or broken terminals.
- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring:
- Erase the 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. 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 not OK:
- Replace the Motronic Engine Control Module (ECM) J623.
- 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. Diagnostic Mode 03 - Read DTC Memory
2. If necessary, erase the DTC memory. Diagnostic Mode 04 - Erase DTC Memory
3. If the DTC memory was erased, generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes

End of Diagnosis