DTC or the Diagnostic Trouble Codes are specific codes used by manufacturers to diagnose certain problems in a vehicle. These are the codes OBD-II scan tools identify and communicate with technicians to help them pinpoint the exact areas of your vehicle's issues. The DTC can be accessed using FORScan. In a video by hackfreehvac, he showed how to diagnose a bad transmission on a Ford E Series van by checking the DTC using FORScan.