Heated Oxygen Sensor Heater Circuit, Checking

Heated Oxygen Sensor Heater Circuit, Checking

• When servicing terminals in the electrical 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 Engine Component Power Supply Relay (J757) OK.

• Fuse (SB9) 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. 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 - arrow -.





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





Specified value: 0 to 20.0 ohms max. (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

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

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

- Remove the Motronic Engine Control Module (ECM) (J220). Refer to => [ Engine Control Module ] Engine Control Module.

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector terminal 3 to the Motronic Engine Control Module (ECM) (J220) electrical harness connector T94 terminal 51 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:

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

- 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) (J220). Refer to => [ Engine Control Module ] Engine Control Module.

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

Final procedures

After the 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.