On-board diagnostics

On-board diagnostics (OBD) is a term referring to a vehicle's self-diagnostic and reporting capability. In the United States, this self-diagnostic is a requirement to comply with federal emissions standards^[1] to detect failures that may increase the vehicle tailpipe emissions to more than 150% of the standard to which it was originally certified.^[2]

A primary benefit of this is that OBD systems give the vehicle owner or repair technician access to the status of the various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since its introduction in the early 1980s versions of onboard vehicle computers. Early versions of OBD would simply illuminate a malfunction indicator light (MIL) or "idiot light" if a problem was detected, but would not provide any information as to the nature of the problem. Modern OBD implementations use a standardized digital communications port to provide real-time data in addition to a standardized series of diagnostic trouble codes, or DTCs, which allow a person to rapidly identify and remedy malfunctions within the vehicle.