Case IH 3967 (DTC 275D) - ECU – Engine Control Unit (ECU): ECU temperature sensor voltage is lower than expected.

The physical signal from the Engine Control Unit's internal temperature sensor (LM71 chip sensor) has fallen below the minimum allowable limit. This can cause the engine to under-fuel, mis-time, or shorten the glow phase.

• MAXXUM T4E
• 7240
• 8240
• 9240
• A8000
• A8800
• Steiger
• Magnum
• Farmall

1. 1

   Check ambient temperature to ensure the machine is not operating in extreme, abnormal freezing conditions that might push the sensor below its physical threshold.

2. 2

   Inspect power and ground circuits for severe voltage drops or bad grounds to the ECU. Check the main battery voltage, ECU power supply relays, and all chassis/engine block grounds.

3. 3

   Inspect the ECU harness for corrosion, water intrusion, or damaged pins at the main ECU connectors.

4. 4

   Use the Electronic Service Tool (EST) to clear the code and retest. If the code returns immediately upon key-on, the internal sensor has failed.

1. 1

   Turn off the machine and disconnect the main battery power

   Turn off the machine and disconnect the main battery power to prevent electrical arcing.

2. 2

   Locate the Engine Control Unit (ECU)

   Locate the Engine Control Unit (ECU) mounted on the side of the engine block.

3. 3

   Unplug the main wiring harness connectors

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

4. 4

   Remove the mounting bolts

   Remove the mounting bolts securing the ECU to the engine block vibration isolators.

5. 5

   Install the new ECU

   Install the new ECU and torque the mounting bolts to factory specifications.

6. 6

   Reconnect the wiring harnesses

   Reconnect the wiring harnesses, ensuring the locking levers click fully into place.

7. 7

   Reconnect battery power

   Reconnect battery power.

8. 8

   Program the new ECU

   A certified Case IH technician must connect the Electronic Service Tool (EST) to flash the blank ECU with the correct engine dataset and injector calibration codes for your specific machine.