Iveco 03F8 – Engine Control Unit (ECU): Exhaust gas temperature sensor circuit fault after filter

Indicates an electrical issue (such as an open circuit, short to ground, or short to voltage) or a complete internal failure of the Exhaust Gas Temperature (EGT) sensor located downstream of the Diesel Particulate Filter (DPF). When this circuit fails, the engine control unit cannot accurately monitor the exhaust temperatures required to safely manage DPF regeneration cycles.

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

1. 1

   Use a diagnostic scan tool to read the live data for the downstream EGT sensor. A failed circuit or unplugged sensor will often default to an implausible extreme negative value (e.g., -40°C or lower).

2. 2

   Visually locate the sensor downstream of the DPF. Ensure you are testing the EGT sensor and not the NOx sensor or particulate sensor, which are also located in the rear exhaust section.

3. 3

   Disconnect the sensor and check the chassis-side wiring harness for proper reference voltage (typically 5V supplied by the ECU) and ground.

4. 4

   Inspect the wiring harness for chafing, melting, or corrosion, which are common near the high-heat environment of the DPF.

1. 1

   Preparation

   Ensure the vehicle is turned off, the battery is disconnected, and the exhaust system has completely cooled down to prevent severe burns.

2. 2

   Disconnection

   Locate the EGT sensor downstream of the DPF. Disconnect the sensor's electrical connector from the wiring harness.

3. 3

   Removal

   Carefully unscrew the faulty sensor from the exhaust pipe. Note: Because these sensors are subjected to extreme heat, they often seize. Penetrating oil may be required.

4. 4

   Preparation of New Sensor

   Lubricate the threads of the new EGT sensor with a high-temperature anti-seize compound (synthetic grease) to prevent future seizing. Ensure no grease gets onto the sensor probe itself.

5. 5

   Installation

   Thread the new sensor into the exhaust pipe by hand to prevent cross-threading, then tighten it to the manufacturer's specified torque.

6. 6

   Reconnection

   Route the sensor cable safely away from direct heat sources and reconnect it to the engine wiring harness.

7. 7

   Clear Codes

   Reconnect the battery, turn the ignition on, and use a diagnostic scan tool to clear the 03F8 fault code from the Engine ECU. Start the engine and verify that the live temperature data is now reading plausibly.