Case IH 2566 – UCM: HST inlet (hydro Gport) - pressure too high

The system has detected an abnormally high hydraulic pressure reading at the hydrostatic transmission (HST) inlet, specifically at the G-port. This can be caused by an electrical issue (such as a failed sensor or wiring fault) or a genuine mechanical overpressure condition in the hydraulic circuit.

• Optum
• Puma series
• Puma 130
• Puma 145
• Puma 160
• Puma CVX
• Maxxum CVT
• Magnum CVT

1. 1

   Check for other error codes and resolve those first

2. 2

   Ensure the tractor battery is not connected to an external power supply (such as a jump starter or heavy-duty charger). Disconnect if present and test for normal operation

3. 3

   Start the engine and run it at 2000 RPM. Check the battery voltage on the instrument cluster; if greater than 15 Volts, there is a charging system fault causing overvoltage

4. 4

   Inspect the hydro Gport pressure sensor connector (e.g., X-916) and the UCM connector (e.g., X-955) to ensure they are securely plugged in, undamaged, and pins are tight

5. 5

   Disconnect the sensor connector and check for a +5 Volt reference signal coming from the UCM

6. 6

   If no electrical faults are found, perform a manual hydraulic pressure test on the system to determine if the pressure is actually too high

1. 1

   Resolve Electrical/Voltage Issues

   If the diagnostic checks reveal damaged wiring, loose pins, or a charging system overvoltage, repair the wiring harness or alternator/regulator as needed.

2. 2

   Replace the Sensor

   If the wiring is intact, the 5V reference is present, and the manual pressure test shows normal hydraulic pressure, the sensor itself has failed. Remove and replace the faulty hydro Gport pressure sensor.

3. 3

   Repair the Hydraulic Circuit

   If the manual pressure test confirms the pressure is genuinely too high, inspect the hydraulic circuit for mechanical faults (such as a stuck relief valve or a restriction in the HST inlet line) and repair as necessary.

4. 4

   Clear Code and Test

   Once the root cause has been rectified, clear the error code from the UCM memory and test the tractor's transmission system for normal operation.