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

The Controller Area Network (CAN) transceiver chip inside the module—or the CAN bus wiring network it communicates on—is detecting a short circuit to a high voltage source (such as a 12V battery line or a 5V sensor reference line).

• MXM
• MXM120
• MXM130
• MXM140
• MXM155
• MXM175
• MXM190
• TM115
• TM175
• TM190
• T7030

1. 1

   Inspect the CAN bus wiring harness connected to the PCU for any chafing, melted insulation, or pinch points that could cause the CAN lines to short to battery voltage (12V) or a 5V reference wire

2. 2

   Inspect the PCU harness connectors for bent pins, corrosion, or water ingress, which can bridge power pins to the CAN communication pins

3. 3

   Disconnect the PCU, turn the key ON, and measure the voltage on the CAN High and CAN Low pins on the harness side to a known good ground (if high voltage is present, the harness is shorted to power)

4. 4

   If the harness tests fine and shows no voltage shorts, conclude that the internal CAN transceiver chip inside the PCU has failed

1. 1

   Disconnect Power

   Disconnect the tractor's battery to prevent further electrical damage during the repair.

2. 2

   Access the PCU

   Locate the Powershift Control Unit (typically located in the cab console/armrest area depending on the exact cab configuration).

3. 3

   Repair Wiring

   If your diagnostic checks revealed a harness short, repair the damaged wiring, replace the blown fuses, and reconnect the system.

4. 4

   Replace the PCU

   If the internal chip has failed, remove the defective PCU and install a replacement unit.

5. 5

   Recalibrate the Transmission

   Reconnect the battery. Because the microprocessor has been replaced, the non-volatile memory is reset. You must perform a transmission/EDC calibration (specifically the H1 clutch and synchronizer calibration) using the tractor's onboard H-Menu or an electronic service tool.

6. 6

   Clear Codes

   Clear the inactive fault codes and test drive the tractor to ensure the transmission shifts correctly and the tAB code does not return.