Oxygen Sensor 1 Heater, Checking

Oxygen Sensor 1 Heater, Checking

The following procedure is used to diagnose Oxygen Sensor (O2S) Heater (Z19) for Heated Oxygen Sensor (HO2S) (G39) which is controlled by the Motronic Engine Control Module (ECM) (J623).

• 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

• Heated Oxygen Sensor (HO2S) Circuit Breaker (S73 ) 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 => [ General Diagnosis ] General Diagnosis.

Start diagnosis

- Raise the vehicle.

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





Checking internal resistance

- 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 Heated Oxygen Sensor (HO2S) (G39). Refer to Fuel Injection and Ignition Repair Information.

If the specification was obtained:

Checking voltage supply

Crank the engine.

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector terminal 4 to Ground (GND) for voltage.









Specified value: Battery voltage.

Switch the ignition off.

If the specification was not obtained:

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

- Check the wiring from the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector terminal 4 to the Engine Component Power Supply Relay (J757) socket 2/87 for a short circuit to each other, Ground (GND), or an open circuit.

- 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. 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 1, Removing and Installing ] Engine Control Module 1, Removing and Installing.

- 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 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.

- If necessary, repair the faulty wiring connection.

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

- Replace the Motronic Engine Control Module (ECM) (J623). Refer to => [ Engine Control Module 1, Removing and Installing ] Engine Control Module 1, Removing and Installing.

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.

- End of diagnosis.