Case IH t50 – Engine Control Unit (ECU) or Instrument Controller: Coolant Temperature Sensor (PHY), Shorted To High Source

The voltage signal coming from the engine coolant temperature sensor is above the normal operating range. This condition is usually caused by a wiring harness problem where the sensor's signal wire is shorted to a positive voltage source (like a 12V supply), or an open circuit (a broken wire or a completely failed sensor).

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• TM120
• TM190

1. 1

   Visually inspect the engine coolant temperature sensor, wiring harness, and electrical connector for visible damage, chafing, corrosion, or loose connections.

2. 2

   Use a multimeter to test the sensor wiring harness for a short to a high voltage source (e.g., 12 volts) or an open circuit/broken ground.

3. 3

   Disconnect the sensor and test its internal resistance with a multimeter to check for an open circuit (infinite resistance) or out-of-spec readings.

4. 4

   Verify the connections at the instrumentation controller/ECU to rule out a controller failure if the sensor and wiring are intact.

1. 1

   Prep the Machine

   Ensure the tractor engine is completely cool and the system is depressurized to prevent severe burns.

2. 2

   Drain Coolant

   Drain a small amount of coolant from the radiator so that the fluid level drops below the sensor port. This prevents coolant from spilling everywhere when the sensor is removed.

3. 3

   Disconnect

   Unplug the electrical connector from the coolant temperature sensor.

4. 4

   Repair Wiring (If Applicable)

   If your diagnostics revealed a short to a high source in the harness, repair or splice the damaged section of the wiring harness.

5. 5

   Remove Sensor

   If the sensor failed the resistance test, use a wrench to carefully unscrew and remove the faulty sensor from the engine block or thermostat housing.

6. 6

   Install New Sensor

   Thread the new OEM coolant temperature sensor into the port. (Apply a liquid thread sealant if the new sensor does not come with pre-applied sealant). Tighten to the manufacturer's torque specification.

7. 7

   Reconnect

   Plug the electrical harness back into the new sensor.

8. 8

   Refill and Test

   Top off the engine coolant to the proper level. Start the tractor, clear the stored fault codes from the ECU, and monitor the dashboard temperature gauge to ensure it reads accurately and the t50 code does not return.