Case IH 3812 (DTC 115D) - ECU – Engine Control Unit (ECU): ECU temperature sensor 1 is too high

The Electronic Diesel Control (EDC) system detects that the internal temperature of the Engine Control Unit has exceeded the maximum safe operating limit, often accompanied by an 'SPI Error' pointing to the internal LM71 sensor.

• MAXXUM T4E
• 240 Series Axial-Flow Combines
• Magnum Series Tractors (180, 200, 220, 240, 250, 280, 310, 340, 380)
• Steiger Series Tractors (370, 420, 470, 500, 620)
• Maxxum Tractors
• Puma Tractors
• Vestrum Tractors
• Case IH Wheel Loaders (1021F, 1121F, 721F)
• Crawler Dozers

1. 1

   Sensor Drift Check (Cold Soak): Connect a diagnostic tool with the ignition ON and the engine OFF (after the machine has sat overnight). Check if the ECU temperature reading matches the ambient temperature. If it reads artificially high when cold, the internal sensor has failed.

2. 2

   Operational Monitoring: Monitor the sensor readings during operation. Look for erratic data, such as the temperature reading too high at low engine loads and too low at high engine loads.

3. 3

   Physical Heat Inspection: Inspect the physical mounting location of the Engine ECU. Ensure that it is not being subjected to abnormal external heat (e.g., missing exhaust heat shields) and that ambient cooling airflow is not obstructed by debris or mud.

1. 1

   Resolve external heat issues

   If the ECU is genuinely overheating due to external factors, resolve the heat shielding or airflow issue to clear the fault.

2. 2

   Disconnect battery

   If the internal LM71 sensor has failed (SPI Error), turn off the machine and disconnect the battery to prevent electrical arcing or data corruption.

3. 3

   Locate ECU

   Locate the Engine ECU on the engine block or firewall.

4. 4

   Disconnect wiring harnesses

   Carefully release the locking tabs and disconnect the main wiring harnesses from the ECU.

5. 5

   Remove faulty ECU

   Unbolt the mounting hardware and remove the faulty ECU.

6. 6

   Install replacement ECU

   Install the replacement ECU and secure the mounting hardware.

7. 7

   Reconnect wiring harnesses

   Reconnect the wiring harnesses, ensuring the locking mechanisms are fully seated.

8. 8

   Reconnect battery

   Reconnect the battery.

9. 9

   Reprogram new ECU

   Connect the Case IH Electronic Service Tool (EST). The new ECU must be flashed/reprogrammed with the correct software, parameters, and injector trim codes specific to the machine.

10. 10

    Verify repair

    Clear the inactive fault codes and run the engine to verify the repair.