Case IH PAB – PCU (Powertrain Control Unit): PCU CAN Chip, Shorted To High Source

The CAN (Controller Area Network) transceiver chip inside the controller has detected a short to a "high source" (typically 12V battery voltage). This prevents the module from transmitting or receiving valid data across the tractor's CAN bus network, as the communication lines are being overpowered by constant high voltage.

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

1. 1

   Inspect the CAN bus wiring harness connected to the PCU for chafed insulation, pinched wires, or areas where the CAN High or CAN Low wires might be shorting against a 12V power supply wire.

2. 2

   Disconnect the PCU and inspect the connector pins for water ingress, green corrosion, or bent pins that could be bridging a 12V power pin to a CAN communication pin.

3. 3

   With the PCU disconnected and the key in the 'ON' position, use a multimeter to measure the voltage on the CAN bus pins in the harness. A full 12V indicates a harness short; normal voltage (around 2.5V) indicates the short is internal to the PCU's CAN chip.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the battery to prevent electrical spikes.

2. 2

   Resolve Wiring (If Applicable)

   If your diagnostic checks revealed a short in the harness, repair the damaged section of wiring, insulate it properly, and reconnect the PCU. Clear the codes and test.

3. 3

   Replace the PCU (If Internal Failure)

   If the wiring is intact, the PCU itself has suffered an internal hardware failure (shorted CAN chip) and must be replaced. Remove the mounting hardware and swap in the new or remanufactured PCU.

4. 4

   Perform Transmission Calibration

   The service manual explicitly states that a Transmission/EDC Calibration setup procedure is required whenever the microprocessor/controller has been replaced.

5. 5

   Calibration Steps

   Ensure the tractor is on level ground with wheels blocked and shift levers in neutral. Hold the High and Low range buttons and start the engine. ''CAL'' will appear in the transmission display. Release the buttons. Set engine speed to 1200 ERPM. Follow the on-screen prompts to calibrate the clutch packs and synchronizers.