Case IH U90 – MTA CCM or APH: Wrong PTO twist installed

The tractor's control module monitors the Power Take-Off (PTO) driveline speed and torque using a PTO twist sensor that reads a rotating exciter ring (twist hub). This code triggers when the module detects an incorrect signal pattern, indicating that the wrong PTO twist hub has been installed on the driveline. Specifically, the system is programmed to read a hub that has exactly 4 fingers (tabs/teeth).

• Farmall 40
• Farmall 45
• Farmall 50
• Farmall 115U Pro EP
• Puma 180-260 CVX
• Magnum 210
• Magnum 235-340 (Series 4)

1. 1

   Visual Hub Inspection: Access the PTO twist sensor location and inspect the tone ring/twist hub on the driveline. Count the number of fingers (tabs). The system requires exactly 4 fingers.

2. 2

   Sensor Inspection: Check the PTO twist sensor itself for physical damage, incorrect installation depth (air gap), or debris buildup on the magnetic tip.

3. 3

   Wiring Check: Inspect the 3-pin connector at the PTO twist sensor for corrosion, backed-out pins, or wiring harness damage (shorts to ground or open circuits can sometimes skew the signal, though they usually trigger 312X series codes).

1. 1

   Preparation

   Park the tractor on a level surface, engage the parking brake, turn off the engine, and disconnect the battery.

2. 2

   Access the Sensor

   Locate the PTO twist sensor on the rear PTO driveline housing. Disconnect the 3-pin electrical connector and unbolt the sensor.

3. 3

   Verify the Hub

   Look through the sensor port (or use a borescope) to count the fingers on the twist hub. If it does not have 4 fingers, the hub must be replaced.

4. 4

   Disassemble PTO Housing

   Drain the hydraulic/transmission fluid as necessary. Remove the rear PTO housing/clutch assembly following the specific model's service manual to gain physical access to the PTO driveline shaft.

5. 5

   Replace the Hub

   Remove the incorrect twist hub from the shaft. Install the correct 4-finger PTO twist hub, ensuring it is seated and secured properly.

6. 6

   Reassembly

   Reinstall the PTO housing and refill the fluids to the correct specification.

7. 7

   Sensor Installation

   Reinstall the PTO twist sensor. Ensure the correct air gap is maintained between the sensor tip and the 4 fingers of the new hub. Reconnect the 3-pin wiring harness.

8. 8

   Calibration & Clearing

   Reconnect the battery. Connect the Case IH diagnostic tool (EST) to clear the U90 fault code. Run the tractor and engage the PTO to verify that the twist sensor is reading correctly and the code does not return.