Iveco 604 – Engine Control Module (ECM) / Engine ECU: Faulty oxygen sensor heater circuit 1

The control module has detected a malfunction in the heater circuit for Sensor 1 (the upstream sensor), typically caused by an open circuit, a short circuit, excessive resistance in the wiring, or a burnt-out heater element inside the sensor itself.

• Iveco Daily
• Iveco Stralis
• Iveco Tector
• Iveco Eurocargo

1. 1

   Inspect the wiring harness and connector leading to Oxygen Sensor 1 for melted wires, corrosion inside the connector pins, or physical damage

2. 2

   Check the vehicle's fuse box for a blown dedicated oxygen sensor heater fuse or relay

3. 3

   Disconnect the sensor, turn the ignition to ON (engine off), and use a multimeter to check the harness side of the connector for 12V power and a solid ground at the heater circuit pins

4. 4

   Using a multimeter, measure the resistance across the heater pins on the oxygen sensor itself to check for an open circuit (infinite resistance/OL) or out-of-spec resistance indicating a failed internal heater element

1. 1

   Preparation

   Disconnect the negative battery terminal. Ensure the exhaust system has cooled down completely to prevent burns.

2. 2

   Locate the Sensor

   Locate Oxygen Sensor 1 (upstream) on the exhaust pipe, typically situated just after the exhaust manifold and before the catalytic converter/DPF.

3. 3

   Disconnect

   Unplug the electrical connector for the oxygen sensor.

4. 4

   Removal

   Use a specialized 22mm offset oxygen sensor socket or a wrench to unscrew the sensor from the exhaust pipe. Tip: If the sensor is seized, apply penetrating oil to the threads and let it sit before attempting to loosen it.

5. 5

   Installation

   Apply a small amount of high-temperature anti-seize compound to the threads of the new sensor (if it doesn't come pre-applied). Do not get any anti-seize on the sensor tip, as this will ruin it.

6. 6

   Tighten

   Thread the new sensor in by hand to prevent cross-threading, then tighten it to the manufacturer's specified torque using the sensor socket.

7. 7

   Reconnect

   Plug the electrical connector back in. Ensure the wiring harness is secured and routed safely away from hot exhaust components.

8. 8

   Clear Codes

   Reconnect the battery, turn the ignition on, and use an OBD/Iveco diagnostic scan tool to clear the 0604 fault code. Start the engine and verify the check engine light remains off.