Case IH t4C – Engine Control Unit (ECU): Coolant Temperature Sensor, Shorted To Low Source

The signal voltage from the engine coolant temperature sensor has dropped below the minimum acceptable threshold. This condition is typically caused by the sensor's signal wire shorting directly to ground, a failure within the wiring harness, or an internal short inside the sensor itself.

• MXM
• Case IH MXM Series (MXM120, MXM130, MXM140, MXM155, MXM175, MXM190)
• Case IH Magnum and MX Series (e.g., MX215, MX230, MX245)
• Case IH Puma and Maxxum Series
• Case IH Steiger Series

1. 1

   Inspect the coolant temperature sensor connector for moisture, corrosion, or bent pins.

2. 2

   Check the wiring harness leading from the sensor to the ECU. Look for areas where the wire insulation may have rubbed through against the engine block or frame, causing a short to ground.

3. 3

   Disconnect the sensor and use a multimeter to check the signal wire for continuity to ground. If continuity to ground exists while disconnected from the ECU, the harness is shorted.

4. 4

   Measure the internal resistance of the coolant temperature sensor. If it reads as a dead short (0 ohms), the sensor has failed internally.

1. 1

   Turn off the tractor and allow the engine and coolant to cool completely to avoid burn injuries.

2. 2

   Locate the coolant temperature sensor, typically threaded into the engine block or thermostat housing.

3. 3

   Disconnect the electrical harness from the sensor.

4. 4

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

5. 5

   If the sensor is internally shorted, prepare to replace it.

   Drain a small amount of coolant from the radiator petcock to bring the coolant level below the sensor port, preventing excessive spills.

6. 6

   Unthread and remove the faulty coolant temperature sensor.

7. 7

   Install the new sensor and tighten to OEM specifications.

   Ensure any required O-rings or thread sealants are in place.

8. 8

   Reconnect the electrical harness.

9. 9

   Refill the cooling system to the proper level.

10. 10

    Start the engine, allow it to reach operating temperature, and verify that the temperature gauge reads correctly and the t4C fault code has cleared.