On-board diagnostics (OBD) is an automotive term referring to a vehicle’s self-diagnostic and reporting capability. 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 on-board vehicle computers. Early versions of OBD would simply illuminate a malfunction indicator light 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.
There are two kinds of on-board diagnostic systems: OBD-I and OBD-II.
OBD-I refers to the first generation OBD systems which were developed throughout the 1980s. These early systems use proprietary connectors, hardware interfaces, and protocols. A mechanic who wanted to access diagnostic information typically had to buy a tool for every different vehicle make. OBD-I scan tools that support multiple protocols are supplied with an array of different adapter cables.
In the early 1990s, Society of Automotive Engineers (SAE) and International Standardization Organization (ISO) issued a set of standards which described the interchange of digital information between ECUs and a diagnostic scan tool. All OBD-II compliant vehicles were required to use a standard diagnostic connector (SAE J1962), and communicate via one of the standard OBD-II communication protocols.
OBD-II was first introduced in model year (MY) 1994 vehicles, and became a requirement for all cars and light trucks starting with MY1996.