Case IH 19114 (DTC 28AA) – Engine Control Unit (ECU) / Dosing Control Unit (DCU): DEF/AdBlue tank temperature sensor plausibility min threshold

The engine's monitoring system has detected an implausible reading from the DEF tank temperature sensor, specifically that the reported temperature has fallen below the minimum acceptable threshold. This is an emissions-related fault that can eventually lead to engine power reduction (derating) if left unresolved.

• MAXXUM T4E
• 240 Series Axial-Flow Combines
• Magnum Series Tractors (e.g., 180, 200, 220, 240, 250, 280, 310, 340, 380)
• Steiger 4WD Tractors (e.g., 370, 420, 470, 500)
• Puma Series Tractors (e.g., 150, 165, 185, 200, 220)
• Maxxum Series Tractors (e.g., 115, 125, 135, 145, 150)
• Farmall Series Tractors (e.g., 90C, 110U, 110A, 120A, 130A, 140A)

1. 1

   Read and save the error log, then erase the code to determine if the fault is active or intermittent.

2. 2

   Inspect the sensor wiring harness for loose contacts, chafing, or physical defects.

3. 3

   Check the electrical connector at the DEF tank for corrosion or pushed-out pins.

4. 4

   Test the DEF tank temperature sensor itself to determine if the internal sensor has failed.

1. 1

   Turn off the equipment and disconnect the battery to ensure safety while working on the electrical system.

   Ensure safety while working on the electrical system.

2. 2

   Locate the DEF tank and the DEF Head Unit assembly (the temperature sensor is typically integrated into this unit alongside the level and quality sensors).

   The temperature sensor is typically integrated into this unit alongside the level and quality sensors.

3. 3

   Disconnect the electrical harness from the DEF Head Unit.

4. 4

   If diagnostic checks revealed a wiring issue, repair the damaged section of the harness or replace the connector.

   Perform this step if diagnostic checks revealed a wiring issue.

5. 5

   If the wiring is intact and the sensor is deemed defective, clean the area around the top of the DEF tank to prevent contamination.

   Perform this step if the wiring is intact and the sensor is deemed defective.

6. 6

   Remove the mounting hardware securing the DEF Head Unit/Quality Sensor to the tank and carefully extract the assembly.

7. 7

   Install the replacement DEF Head Unit, ensuring the sealing gasket is properly seated.

   Ensure the sealing gasket is properly seated.

8. 8

   Reconnect the electrical harness and reconnect the battery.

9. 9

   Use a diagnostic tool to clear the fault codes and run the machine to verify that the DEF temperature reads accurately and the engine does not derate.

   Verify that the DEF temperature reads accurately and the engine does not derate.