Case IH 2618 – Instrument Controller (INST) or Transmission Controller (Trans): Transmission oil temperature sensor is open circuit or shorted to power

The control module is detecting that the voltage signal from the transmission oil temperature sensor is too high. This indicates an open circuit (infinite resistance) or that the signal wire has rubbed against a power wire and is receiving direct voltage (shorted to power / B+). The controller cannot monitor the CVT or powershift transmission fluid temperature, which is critical to prevent overheating and hydrostatic damage.

• Steiger T4B
• Magnum Series: MX series, 235–340 (Series 4)
• Steiger Series: 350–600
• Puma Series
• Farmall Series: 95U, 105U, 115U Pro EP, JX Series

1. 1

   Verify active fault codes in the instrument (INST) or transmission controller to confirm the circuit is actively failing.

2. 2

   Visually inspect the transmission oil temperature sensor (near clutch/4WD solenoid valves) and its electrical connector for backed-out pins, corrosion, or water ingress.

3. 3

   Check for an open circuit by disconnecting the sensor and using a multimeter to test continuity between the sensor connector and the corresponding pin on the controller harness.

4. 4

   Check for a short to power by measuring voltage on the signal wire with the sensor disconnected and key ON (should not read full 12V or steady 5V reference).

5. 5

   Test the sensor internally by measuring resistance across its terminals; a reading of 'OL' indicates internal failure.

1. 1

   Preparation

   Park the machine on a level surface, engage the parking brake, and turn off the engine. Allow the transmission oil to cool to a safe temperature.

2. 2

   Clean the Area

   Thoroughly clean the area around the transmission oil temperature sensor on the transmission housing to prevent dirt from entering the hydraulic circuit.

3. 3

   Disconnect

   Unplug the electrical connector from the temperature sensor.

4. 4

   Removal

   Unscrew the faulty sensor from the transmission housing. Note: Have a catch pan ready, as a small amount of transmission fluid may leak out when the sensor is removed.

5. 5

   Installation

   Thread the new OEM transmission oil temperature sensor into the port and tighten to the manufacturer's torque specification.

6. 6

   Reconnection

   Plug the electrical connector back into the new sensor, ensuring the locking tab clicks into place.

7. 7

   Fluid Check

   Check the transmission/hydraulic oil level and top off if any fluid was lost during the swap.

8. 8

   Clear Codes

   Turn the key ON and use the diagnostic interface or armrest display to clear the inactive fault codes from the INST or Transmission controller. Start the tractor and verify the temperature reads correctly without throwing a code.