Case IH tB3 – PCU (Powertrain Control Unit): Vehicle CAN Bus Off, Shorted To High Source

The Controller Area Network (CAN) bus has shut down because one of the communication lines is shorted to a high voltage source (such as the 12V battery supply). When this happens, the network values fall outside expected limits, and the modules can no longer communicate with one another.

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

1. 1

   Measure the resistance across the CAN bus with the key off to ensure the terminating resistors are intact

2. 2

   Inspect the wiring harness for rubbed or chafed areas, particularly under the cab or at bad connectors

3. 3

   Verify that all modules have proper power and ground connections

4. 4

   With the key on, check the voltage of the CAN data buses (a healthy CAN bus typically shows around 2.4V to 2.5V on both the yellow and green data lines)

5. 5

   Disconnect the modules on the network one by one to see which one is shorting the bus to a high source

1. 1

   Visual Inspection

   Start by visually inspecting the entire CAN bus circuit for physical damage. Look for exposed wires that may be shorting directly to a 12V power source.

2. 2

   Module Isolation

   If the wiring harness is intact, disconnect each controller individually. If the instrument cluster or a specific module comes back online after a specific controller is unplugged, that controller (or its immediate connector) is the source of the short.

3. 3

   Repair or Replace

   Repair the shorted wiring harness section, or replace the internally shorted control module.

4. 4

   Clear Codes

   Use a diagnostic service tool to clear the fault codes from the modules and retest the system.

5. 5

   Recalibrate (If Applicable)

   If the microprocessor/PCU was replaced, or if the non-volatile memory was reset, you must perform the Transmission/EDC Calibration Set Up Procedure. The transmission display will likely show an error code (like F24 or 24) indicating that calibration is required.