BUS BAR GP 3978843 - Caterpillar

This diagnostic code is recorded when the PL522 or 523 detects a problem that is internal to the control module. This diagnostic code can only be caused if the ECM for PL522 or 523 is faulty. There are no serviceable parts within the control module.Test Step 1. CHECK THE HARNESS CONNECTIONS.
Disconnect the contacts and clean the contacts of the harness connectors.
Reconnect all harness connectors.
Turn the key start switch to the ON position.
Operate the machine.
Determine if "CID 0254 FMI 12" diagnostic code is present by using Cat ET . Expected Result:The "CID 0254 FMI 12" diagnostic code is present.Results:
OK - The "CID 0254 FMI 12" diagnostic code is present.Repair: The problem has not been corrected. ECM failure is unlikely. Perform this diagnostic test procedure again. If the cause of the diagnostic code is not found, replace the PL522 or 523 ECM. Before replacing the PL522 or 523, contact your Caterpillar Technical Communicator. Refer to Systems Operation, Troubleshooting, Testing and Adjusting , "Electronic Control Module (ECM) - Replace".STOP
NOT OK - The "CID 0254 FMI 12" diagnostic code is not present. The problem does not exist at this time. The initial problem was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.STOP