Case IH 3965 – Engine Control Unit (ECU) / Electronic Diesel Control (EDC): ECU temperature sensor 2 is too low

The secondary internal temperature sensor located inside the engine control module is reporting a temperature value that falls below the valid operating range, or the sensor's internal circuit is experiencing a low voltage condition (often caused by an internal short or component failure).

• Steiger T4B
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• A8000 / A8800 Sugar Cane Harvesters
• Various Case IH tractors

1. 1

   Check live data using the Case IH Electronic Service Tool (EST) or the in-cab AFS Pro 700 display to monitor the ECU Temperature Sensor 2 reading.

2. 2

   Ensure the ECU is not exposed to extreme freezing conditions that might legitimately trigger a 'too low' reading.

3. 3

   Verify the machine's battery voltage and inspect the main ground connections to the ECU, as poor grounding can skew internal sensor voltage readings.

4. 4

   Disconnect the ECU harnesses and check for moisture, water intrusion, or corrosion on the pins, which can cause internal board shorts.

5. 5

   Perform a key cycle or an emergency re-start to see if the code is an intermittent glitch.

1. 1

   Turn off the machine and disconnect the main battery power

   This prevents electrical arcing.

2. 2

   Locate the Engine Control Unit (ECU)

   The ECU is located on the engine block or mounting bracket.

3. 3

   Unplug the wiring harness connectors from the ECU

   Carefully release the locking levers on the wiring harness connectors and unplug them.

4. 4

   Remove the defective ECU

   Remove the mounting bolts securing the ECU and remove the defective unit.

5. 5

   Install the replacement ECU

   Install the new unit and tighten the mounting hardware.

6. 6

   Reconnect the wiring harnesses

   Ensure the locking levers are fully seated.

7. 7

   Reconnect the battery

8. 8

   Perform dealer programming

   A certified Case IH technician must connect the EST diagnostic laptop to flash the correct engine dataset, write the specific fuel injector codes to the new ECU, and clear any residual codes.