Case IH F-3031-00 - ECU – Engine Control Unit (ECU): DEF (Diesel Exhaust Fluid) / AdBlue tank temperature sensor circuit has failed high

The control module has detected that the voltage signal from the temperature sensor is higher than the expected normal operating range. This condition typically points to an electrical issue such as an open circuit, a disconnected sensor, a damaged wiring harness, or a short to a high-voltage source, rather than a mechanical failure.

• MAGNUM AFS Connect
• Magnum
• Steiger
• Puma
• Maxxum
• Optum
• Axial-Flow 140 series
• Axial-Flow 240 series
• Compact track loaders

1. 1

   Inspect the DEF tank sender unit and its wiring harness for any signs of physical damage, chafing, or corrosion.

2. 2

   Disconnect the sensor connector and check for corroded, bent, or loose pins. Look for moisture or DEF crystallization inside the connector.

3. 3

   Use a multimeter to verify the power supply and ground circuits at the sensor connector to ensure the sensor is receiving the correct voltage from the ECU.

4. 4

   Test the wiring harness between the DEF sender unit and the ECU for continuity and ensure there is no short to a high-voltage source.

5. 5

   Perform a resistance check on the DEF tank temperature sensor pins to confirm if the internal thermistor has failed (open circuit).

6. 6

   Use the CNH Electronic Service Tool (EST) diagnostic software to view live ECU data. If the temperature reading shows an implausibly high or default extreme value, the sensor or circuit is confirmed open.

1. 1

   Power down the machine, remove the key, and disconnect the battery to ensure electrical safety.

   Ensure electrical safety before beginning the repair.

2. 2

   Locate the DEF tank on the machine and identify the DEF sender unit mounted on the top of the tank.

   The DEF temperature sensor is typically integrated into the DEF Sender Unit (also known as the DEF Head Unit).

3. 3

   Carefully disconnect the electrical wiring harness connector from the DEF sender unit.

   Disconnect the electrical connection.

4. 4

   Disconnect the DEF fluid lines attached to the head unit, noting their positions. Cap the lines to prevent contamination.

   Note positions and cap lines to prevent contamination.

5. 5

   Thoroughly clean the area around the sender unit flange to prevent dirt, debris, or crystallized DEF from falling into the tank during removal.

   Clean the flange area thoroughly.

6. 6

   Remove the mounting bolts or unscrew the locking ring securing the sender unit to the DEF tank.

   Unfasten the sender unit.

7. 7

   Carefully lift the old DEF sender unit out of the tank, allowing excess fluid to drain back into the tank.

   Remove the old unit and let fluid drain.

8. 8

   Install the new DEF sender unit into the tank, ensuring that a new mounting seal/O-ring is used to prevent leaks.

   Always ensure the replacement unit includes a new tank mounting seal.

9. 9

   Secure the unit with the mounting bolts or locking ring.

   Fasten the new sender unit.

10. 10

    Reconnect the DEF fluid lines and the electrical harness connector.

    Restore fluid and electrical connections.

11. 11

    Reconnect the battery, turn the ignition to the ON position, and use a diagnostic scan tool to clear the F-3031-00 fault code. Verify that the live DEF temperature reading is now within the normal ambient range.

    Clear the fault code and verify the repair.