On-board Diagnostics

On-board diagnostics, or OBD, is an automotive term referring to a vehicle's self-diagnostic and reporting capability. OBD systems give the vehicle owner or a repair technician access to state of health information for various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since the introduction in the early 1980s of on-board vehicle computers, which made OBD possible. Early instances of OBD would simply illuminate a malfunction indicator light, or MIL, 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 one to rapidly identify and remedy malfunctions within the vehicle.

Read more about On-board Diagnostics:  History, OBD-II Signal Protocols, OBD Applications, Security Issues

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On-board Diagnostics - Security Issues
... There have been reports of thieves using specialist OBD reprogramming devices to enable them to steal cars without the use of a key ... The primary causes of this vulnerability lie in the tendency for vehicle manufacturers to extend the bus for purposes other than those for which it was designed, and the lack of authentication and authorization in the OBD specifications, which instead rely largely on security through obscurity ...