Oxygen Sensor Before Catalytic Converter, Checking

Diagnostic Procedures

Oxygen Sensor before Catalytic Converter, Checking

• Use only gold-plated terminals when servicing terminals in the electrical harness connector of the Heated Oxygen Sensor (HO2S) (G39 ).

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

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

• The Oxygen Sensor (O2S) Heater (Z19) before catalytic converter 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 connections between engine/transmission/chassis OK.

• Exhaust system between catalytic converter and cylinder head properly sealed.

• Coolant Temperature at least 80° C.

Test procedure

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check

Start diagnosis

- Perform the function test in Diagnostic Mode 06.

If specified values are obtained:

- Check for possible intermittent connection or rub through of harness.

- Erase the code. Drive the vehicle and generate the readiness code.

If the specified value was Not obtained:

Checking primary voltage

- Disconnect the Heated Oxygen Sensor (HO2S) (G39 ) electrical harness connector - 1 -.





- Using a multimeter, connect the negative lead to engine ground. Start the engine, and check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector terminals 2, 3, 4 and 6 for voltage.





Specified value: 2.40 V - 4.99 V

- Switch the ignition OFF.

If the specified value was obtained:

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

If the specified value was Not 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) ( J220). Refer to the Repair Information.

- Using a multimeter, check the Heated Oxygen Sensor (HO2S) (G39) electrical harness connector terminals to the Motronic Engine Control Module (ECM) (J220) electrical harness connector T121 terminals for an open circuit.









Specified value: 1.5 ohms Max.

If the specified value was Not obtained:

- Check the wiring for an open, high resistance, short circuit to each other, Battery (+) or Ground.

- 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 and the voltage was Not OK:

- Replace the Motronic Engine Control Module (ECM) (J220). Refer to the Repair Information.

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 Modes 01 - 09.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Monitors, Trips, Drive Cycles and Readiness Codes.