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

The Powertrain Control Unit has taken itself off the Controller Area Network (CAN) bus because it detected a short circuit to a high voltage source (such as a 12V battery line or a 5V sensor reference line) on the CAN communication lines. To protect the network and itself, the module shuts down its CAN communication.

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

1. 1

   Check for companion codes (e.g., tAC, tAE, tAF, tB0, tB1, tB2, tB3) to determine if it is a network-wide wiring issue or an isolated PCU fault

2. 2

   Visually inspect the CAN bus wiring harness leading to the PCU for chafing, melted insulation, or pinched wires

3. 3

   Disconnect the PCU and inspect the connector pins for water ingress, corrosion, or bent pins bridging a power terminal to a CAN terminal

4. 4

   With the battery disconnected, use a multimeter to test the CAN lines at the PCU connector for continuity to power circuits

5. 5

   Verify the CAN bus terminator resistors are intact and reading the correct resistance (typically 60 ohms across the network)

1. 1

   Disconnect Power

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

2. 2

   Isolate the Short

   If your multimeter test reveals a short to a high voltage source on the CAN lines, systematically unplug other modules on the bus to see if the short disappears. If it does, the last unplugged module or its harness branch is the culprit.

3. 3

   Repair Wiring

   If a damaged wire is found, repair the harness by splicing and heat-shrinking the affected area. Ensure the harness is routed away from heat sources and sharp frame edges.

4. 4

   Test the PCU

   If the wiring harness tests perfectly fine and the short is only present when the PCU is plugged in, the internal circuitry of the PCU has failed and is shorting the CAN transceiver to power. The module must be replaced.

5. 5

   Reassembly & Clearing

   Reconnect the harness and battery. Clear the fault codes via the H-Menu diagnostic interface.

6. 6

   Recalibration

   If the PCU was replaced or its non-volatile memory was reset, you MUST perform a Transmission/EDC Calibration. Ensure the tractor is at operating temperature (20–50°C), the parking brake is applied, A/C is off, and all electrical/hydraulic services are deselected before initiating the calibration sequence.