Oxygen Sensor Heaters Before Catalytic Converter, Checking

Oxygen Sensor Heaters Before Catalytic Converter, Checking

This procedure is used to check Oxygen Sensor (O2S) Heater Z19 or Oxygen Sensor (O2S) Heater Z28.

NOTE: When servicing terminals in harness connector of Heated Oxygen Sensors (HO2S) , 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 Heated Oxygen Sensor (HO2S) 2 G108 fuse 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. General Diagnosis

Start diagnosis







- Disconnect the Oxygen Sensor (O2S) Heater Z19 electrical harness connector - 1 -.

To disconnect the Oxygen Sensor (O2S) Heater -Z28- , perform the following steps:







- Remove the screw - arrow - retaining the coolant reservoir.
- Disconnect the Engine Coolant Level (ECL) Warning Switch F66 electrical connector from the bottom of the coolant reservoir and set aside the coolant reservoir with the coolant hoses - 1 - and - 2 - connected.







- Disconnect the Oxygen Sensor (O2S) Heater -Z28- electrical harness connector - 2 -.

Checking internal resistance







- Using a multimeter , check the Heated Oxygen Sensor (HO2S) terminals 3 to 5 for resistance.

Specified value: 2.5 to 10.0 Ohms (at approx. 20 degrees C)

If the specification was not obtained:
- Replace the faulty Heated Oxygen Sensor (HO2S) before the catalytic converter.

If the specification was obtained:

Checking voltage supply

Switch the ignition on.

- Using a multimeter , check the Heated Oxygen Sensor (HO2S) electrical harness connector terminal 5 to the Engine Component Power Supply Relay J757 terminal 2/87 for voltage.

Heated Oxygen Sensor (HO2S) Engine Component Power Supply Relay
electrical harness connector J757 electrical harness connector
terminal terminal
5 2

Switch the ignition off.

Specified value: Battery voltage.

If the specification was not obtained:
- Check the wiring for a short circuit to each other, Ground (GND), or an open circuit.
- 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 Engine Control Module (ECM) J623.







- Using a multimeter , check the Oxygen Sensor (O2S) Heater electrical harness connector terminal to the Engine Control Module (ECM) J623 electrical harness connector T94 for an open circuit.

Oxygen Sensor (O2S) Heater Engine Control Module (ECM) J623
Z19 electrical harness electrical connector T94 terminal
connector terminal or test box socket
3 51

Oxygen Sensor (O2S) Heater Engine Control Module (ECM) J623
Z28 electrical harness electrical connector T94 terminal
connector terminal or test box socket
3 73

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 Engine Control Module (ECM) J623.

Assembly is performed in reverse order of removal, note the following:

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.