Since the early 1980s, car manufacturers have used a computer-based PCM (power-train-control module) to control the fuel and ignition system in your car. Tightened emissions standards have forced car makers to put sophisticated pollution-control systems under the PCM's supervision as well. As the PCM system grew in complexity, engineers added onboard diagnostics to help technicians trou-bleshoot malfunctioning engines. Today, onboard computers play such an important role in reducing vehicle emissions that, since the 1994 model year, the US EPA (Environmental Protection Agency) has established requirements for OBD (onboard-diagnostic) systems. The latest system, OBD II, has been standard equipment on US light-duty cars and trucks since the 1996 model year.
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