Case IH tAD – PCU (Powertrain Control Unit): PCU CAN Bus Off, Shorted To High Source

The Controller Area Network (CAN) bus communication lines connected to the PCU have shut down ("Bus Off") because the system has detected a short circuit to a high voltage source (typically 12V battery power).

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

1. 1

   Inspect the transmission/chassis wiring harness leading to the PCU for visible damage, rubbing, or pinched wires that could expose the CAN bus wires to a 12V power source.

2. 2

   Disconnect the PCU and use a multimeter to test the CAN High and CAN Low pins on the harness side. Check for inappropriate voltage (a short to battery power) with the key ON.

3. 3

   If voltage is present on the CAN lines while the PCU is unplugged, the short is in the wiring harness. If the harness tests clean but the code returns immediately when the PCU is plugged back in, the internal CAN transceiver inside the PCU has failed and is shorting the bus.

1. 1

   Disconnect Power

   Disconnect the tractor's battery before servicing the electrical system or removing modules.

2. 2

   Repair Wiring

   If a short to power was found in the harness during diagnostics, repair the damaged wire section or replace the affected harness segment.

3. 3

   Replace the PCU

   If the wiring is intact and the PCU is internally shorted, remove the faulty Transmission Control Module and install the replacement unit.

4. 4

   Perform Calibration

   Enter the H-Menu (Calibration/Configuration) and perform the transmission calibration (bringing engine speed to 1200 ERPM and following the display prompts) to sync the new controller to the tractor's clutch packs and synchronizers.