Case IH PCB – PCU (Power Control Unit): CAN In PCU, Shorted To High Source

Indicates a critical electrical fault where the Controller Area Network (CAN) bus communication lines going into the PCU are experiencing a short circuit to a high voltage source (typically the 12V battery power). This disrupts the data network, preventing the PCU from communicating properly with other modules on the machine.

• MXM
• Case IH MXM 120
• Case IH MXM 130
• Case IH MXM 135
• Case IH MXM 140
• Case IH MXM 150
• Case IH MXM 155
• Case IH MXM 165
• Case IH MXM 175
• Case IH MXM 180
• Case IH MXM 190
• Case IH MX Series
• Case IH TG Series

1. 1

   Visual Harness Inspection: Trace the CAN bus wiring harness leading to the PCU. Look for chafed insulation, pinched wires, or bare spots where a CAN line might be rubbing against a 12V power wire or a hot terminal.

2. 2

   Connector Inspection: Disconnect the PCU harness and inspect the pins. Look for water ingress, corrosion, or bent pins that could be bridging a power supply pin to a CAN High or CAN Low pin.

3. 3

   Multimeter Voltage Test: With the key ON (and PCU disconnected), probe the CAN lines on the harness side. If you see a full 12V on the CAN lines, the short is in the wiring harness.

4. 4

   Module Isolation: If the harness tests fine, the short may be internal to a module. Disconnect other modules on the CAN bus one by one to see if the short-to-high condition clears. If the short only exists when the PCU is plugged in, the PCU has an internal short.

1. 1

   Disconnect Power

   Turn off the tractor and disconnect the negative battery cable to prevent further electrical damage.

2. 2

   Access the PCU

   Locate the Transmission Control Module / PCU (typically located under the right-hand console or cab floor depending on the exact MXM model).

3. 3

   Repair Wiring (If Applicable)

   If the diagnostic checks revealed a short in the harness, splice and repair the damaged CAN wires using proper heat-shrink connectors, or replace the damaged harness section.

4. 4

   Replace the PCU (If Applicable)

   If the PCU has an internal short, unbolt the module and install the replacement unit.

5. 5

   Reconnect and Clear

   Reconnect the battery. Turn the key switch to the "ON" position and use the Electronic Service Tool (EST) or the tractor's H-Menu to clear the stored fault codes.

6. 6

   Perform Calibration

   If the PCU was replaced, or if non-volatile memory was reset, you must perform the Transmission/EDC Calibration Set Up Procedures. This includes the "H1 Clutch and Synchroniser Calibration". Note: To calibrate, the transmission oil must be at operating temperature. Hold the High and Low range buttons and start the engine until "CAL" appears, set engine speed to 1200 RPM, and follow the on-screen prompts to calibrate the clutches.