Diagnostic Trouble Codes
There are three DTC types used by the CAN networks.

Internal error DTCs | The ECUs run internal checks. If one finds that there is an internal ECU problem, it will set an internal error DTC. This indicates that the ECU needs to be replaced.
Loss ofcommunication DTCs | Loss of communication DTCs (and Bus-off DTCs) are set when there is a problem with the communication between ECUs. This could be in the connections, the wiring, or the ECU (as called out in the DTC Troubleshooting).
Signal error DTCs | The ECUs can run diagnosis on some input circuits to determine if that circuits are functioning properly (no opens or shorts). If a circuit falls the diagnostic test, a DTC will set (NOTE: Not all input circuits are tested for errors).