Computerized Engine Diagnostics

Automobiles manufactured since the early 1980s are equipped with "smart" systems, known as on-board diagnostics. On-board diagnostics, or OBD, systems were developed to help repair technicians identify problems associated with the computerized engine systems of modern vehicles. These systems are made up of various sensors and a computer that communicates its findings to a technician by means of diagnostic trouble codes that are stored in the automobile's computer.

The federal Clean Air Act Amendments of 1990 required all 1996 and newer light duty vehicles to have more advanced OBD systems, known as OBD II. The OBD system monitors vehicle conditions and components that are related to vehicle emissions, such as the catalyst in the catalytic converter, engine misfire, the engine coolant temperature, and the oxygen sensors. Federal law requires some states that do not meet federal air quality standards to implement an emission inspection program to ensure that emissions control equipment is operating correctly.