Case IH tC9 – PCU (Power Control Unit): PTO Twist Speed Sensor Over Voltage

The controller is receiving a voltage signal from the PTO twist speed sensor that exceeds the normal operating range, typically indicating a short to a high-voltage source in the sensor's circuit.

• MXM
• MXM 120
• MXM 130
• MXM 140
• MXM 155
• MXM 175
• MXM 190
• Maxxum
• Puma

1. 1

   Check for related codes that might point to a broader harness issue or calibration loss (e.g., U50, U58, U59, TC7)

2. 2

   Inspect the wiring harness between the PTO twist speed sensor and the PCU for chafed wires, melted insulation, or pinched harnesses

3. 3

   Disconnect the sensor and check the connector pins for corrosion, moisture, or debris that could bridge the power and signal terminals

1. 1

   Isolate the Short

   Disconnect the PTO twist speed sensor. Use a multimeter to check the voltage on the signal wire of the machine-side harness with the key ON. If it reads high voltage (e.g., 12V) with the sensor unplugged, the short is in the wiring harness.

2. 2

   Repair Wiring

   If a short to power is found in the harness, repair the damaged section of the wire or replace the affected harness segment.

3. 3

   Replace the Sensor

   If the wiring harness tests good (no short to power on the signal wire), the internal circuitry of the PTO twist speed sensor has likely failed and shorted internally. Remove and replace the sensor.

4. 4

   Recalibrate

   After repairing the wiring or replacing the sensor, you must perform the electronic calibration procedure (often referred to as the H8 procedure, where the default calibration value is set to 3999).