OBD2 is the second generation of On-Board Diagnostic system. All cars manufactured and sold in the U.S. in 1996 and later have 16-pins connector under the dash. (the locations of the connector is different, depending on models, makes and years) This connector is called Data Link Connector or DLC. DLC connects to a vehicle’s computer that is monitoring condition of the car by collecting sensor readings from sensors. And It is also controlling fuel economy, emission system, even acceleration and brake system. When one or more sensor’s reading exceeds the limit of its specification, vehicle’s computer warn you by turning on a yellow light in an instrument panel. This light is called Malfunction Indicator Light or MIL. In some cars, the light says Check Engine or Service Engine Soon in the instrument panel, people usually call it Check Engine Light. So, what is OBD2 different from OBD1?
First generation of On-Board Diagnostic system (OBD-I) also have MIL. But all it can do is turn on MIL and warn you that something is wrong with your car. It cannot detect a failure on an evaporative system or a catalytic converter. OBD2 can detect more system failures than OBD-I can do. OBD2 system can show you what system is faulty and readings of all sensors through scan tools. To get these information, you need a OBD2 scan tool that connects to DLC and then vehicles computer.
Modern cars are getting more and more computer-controlled machinery, haveing less physical parts controlled by you. Thus, OBD2 diagnostics is very important and critical in auto repair industry.