Case IH 2678 (518576.02) - DEC – Transmission Control Unit (TCU): Synchro R1/F2 (F2-R1) Position Sensor Open Circuit

Indicates an "open circuit" condition in the Synchro R1/F2 (also referred to as F2-R1) Position Sensor circuit. The transmission controller monitors this sensor to determine the physical position of the synchronizer responsible for engaging the F2 (Forward 2) and R1 (Reverse 1) gears. An open circuit means the controller has lost the signal from the sensor, typically due to a disconnected plug, a broken wire, or an internal failure of the sensor itself.

• VESTRUM CVX
• Magnum 210
• Magnum 220
• Magnum 235
• Magnum 255
• Magnum 285
• Magnum 340
• Magnum 385

1. 1

   Locate the Synchro F2-R1 position sensor on the top or right-hand side of the transmission case.

2. 2

   Inspect the 3-pin connector (RAC Bosch BDK 2.8 3-way) for pushed-out pins, corrosion, or moisture.

3. 3

   Verify 5V Sensor Supply: Using a multimeter with key ON, check Pin 2 (Green wire, circuit 7525) for a steady 5.0V reference voltage.

4. 4

   Verify Sensor Ground: Check Pin 3 (Black/White wire, circuit 60) for good continuity to ground.

5. 5

   Verify Signal Wire: Check Pin 1 (Blue wire, circuit 7584) for continuity between the pin and the transmission controller.

6. 6

   Ensure the sensor is not physically bound up where it passes through the transmission case, preventing proper synchro engagement.

1. 1

   Park the tractor on a level surface, engage the parking brake, and turn the key to the OFF position.

   Ensure the machine is safely secured before beginning work.

2. 2

   Access the top/right-hand side of the transmission to locate the Synchro F2-R1 position sensor.

   Locate the sensor on the transmission case.

3. 3

   Disconnect the 3-pin wiring harness connector (X-533).

   Unplug the sensor from the main harness.

4. 4

   If the diagnostic checks above confirmed that the 5V supply, ground, and signal wires are intact, the sensor has failed internally (open circuit).

   Confirm internal sensor failure based on prior electrical checks.

5. 5

   Remove the retaining hardware holding the sensor to the transmission case.

   Unbolt the sensor from its mounting location.

6. 6

   Carefully pull the sensor straight out of the transmission housing.

   Remove the old sensor.

7. 7

   Lubricate the O-ring on the new sensor with clean transmission fluid and install it into the transmission case, ensuring the mechanical linkage aligns properly with the synchronizer rail without binding.

   Install the new sensor carefully to avoid binding the mechanical linkage.

8. 8

   Secure the retaining hardware.

   Bolt the new sensor into place.

9. 9

   Reconnect the 3-pin wiring harness.

   Plug the connector back into the sensor.

10. 10

    Turn the key ON, clear the stored fault codes using the tractor's diagnostic display or a service tool, and perform a transmission calibration if required by the operator's manual to relearn the synchro end-stops.

    Clear codes and calibrate the transmission to finalize the repair.