Diagnostic Trouble Code

An electronic signal stored in a vehicle's On-Board Diagnostic (OBD) computer, indicating the presence of a fault. All manufacturers use the same DTC naming standards — for example, a P0171 code means the same thing on a Ford as it does on a Hyundai or BMW. As OBD systems have been around since 1996, most repair technicians have the equipment and training necessary to read diagnostic trouble codes.