Case IH t4B – Engine Control Unit (ECU): Coolant Temperature Sensor, Open Circuit Or Current Below Normal Range

The control module is detecting infinite resistance (an open circuit) or a current draw that is lower than the expected operating threshold on the coolant temperature sensor circuit. This is typically caused by a disconnected sensor plug, a broken wire in the harness, or a sensor that has failed internally.

• MXM
• MXM Series
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190
• Puma
• Magnum

1. 1

   Visually inspect the wiring harness leading to the engine coolant temperature sensor for disconnected plugs, chafed wires, or corrosion inside the connector pins.

2. 2

   Disconnect the sensor and measure its internal resistance across the pins using a multimeter (20 C = 4200 ohms, 40 C = 900 ohms, 60 C = 780 ohms, 80 C = 500 ohms, 100 C = 280 ohms). If the sensor reads open/infinite resistance, it is defective.

3. 3

   If the sensor tests within specification, check the wiring harness for continuity between the sensor connector and the ECU to isolate a broken wire.

1. 1

   Cool Down

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

2. 2

   Locate and Disconnect

   Locate the coolant temperature sensor on the engine block or thermostat housing. Disconnect the electrical wiring harness.

3. 3

   Remove Sensor

   Unthread the faulty sensor. Have a catch pan ready to collect any coolant that escapes from the port.

4. 4

   Install New Sensor

   Thread the new OEM coolant temperature sensor into the port. According to the NEF Engine Service Manual, if it is an M14 threaded sensor, torque it to 17 - 23 Nm (12.5 - 17.0 lb ft).

5. 5

   Reconnect

   Plug the electrical connector back into the sensor, ensuring it clicks and locks into place.

6. 6

   Refill Coolant

   Top off the engine coolant reservoir to replace any fluid lost during the swap.

7. 7

   Clear and Test

   Turn the ignition on, clear the stored t4B fault code from the diagnostic menu, and run the engine to verify the temperature gauge operates correctly and the code does not return.