Second-generation onboard diagnostics, more commonly known as OBDII, is a sophisticated onboard computer system that was first used on some 1994 and 1995 model vehicles. Since 1996, it is used on all makes and models and cars and light trucks. OBDII uses a network of sensors to monitor operating conditions.
Government agencies mandated the application of OBDII technology to keep tighter reins on vehicle emissions. In addition, OBDII brings about certain standards intended to help streamline the diagnostic process, regardless of the make of vehicle. The system also alerts you with a Malfunction Indicator Lamp (MIL), indicating that the system has detected a problem, which could cause excessive emissions. This light is usually labelled SERVICE ENGINE SOON or CHECK ENGINE. If the light appears, you should have its cause investigated by a professional technician at your earliest opportunity. If the light flashes, the condition is more severe and must be checked out immediately to prevent damage to the catalytic converter.
Perform routine maintenance as recommended in your owner's manual. The onboard computer, otherwise know as the powertrain control module, stores a Diagnostic Trouble Code (DTC) when it detects a problem in one of the monitored circuits. A professional technician can access this information using a scan tool connected to the vehicle's Data Link Connector (DLC). Although many DTCs are sensor-related, it does not necessarily indicate a faulty sensor. There may be problems in that sensor's circuit, or there may be several interrelated problems. Areas of the country with an emissions testing program are placing added value on OBDII checks, where this technology may be used in place of tailpipe testing.