OBD stands for onboard diagnostics and OBD-II is a collection of connection and protocol standards standards for all cars sold since 1996, when the OBD-II specification was made mandatory by the U.S. government.
OBD technology was born out of the Environmental Protection Agency's (EPA) and California Air Resources Board's (CARB) mandate that vehicles equipped with more-sophisticated emissions equipment and better diagnostics systems to monitor that equipment. The agencies wanted to ensure that new vehicles were running as cleanly and efficiently as they could. However, purchasing diagnostics equipment for each of the manufacturers' proprietary vehicle information systems would be prohibitive for third-party garages and testing centers. Thus, the OBD standard (and the subsequent OBD-II revision) was born.
The first part of the OBD-II standard is the connector. The 16-pin female interface connector must be located in the vehicle's cabin within 2 feet of the steering wheel. For most cars, this means in the driver's foot well or just below the steering wheel. Although, the physical connection is always the same in OBD-II-compliant vehicles, not all of the 16 pins are always utilized and the data isn't always sent over those pins in exactly the same manner, so there is some variation within the standard. Specifically, there are five major signaling protocols for vehicles sold in the United States between 1996 and 2008 that can usually be discerned by the configuration of pins used. New legislation has narrowed these five variations down to one, ISO 15765 CAN, for all vehicles sold after 2008, so the OBD-II standard is decidedly more standard from that point forward.
Outside of the US OBD-II standard there are also the European EOBD and EOBD2 standards and the Japanese JOBD standards.
What does it do?
Where the real work of the OBD-II standard takes place is within the data sent over the connection. During normal operation, your vehicle is constantly monitoring a little more than 100 standard Parameter ID (PID) codes. Every vehicle must be capable of sending or receiving these codes over its OBD-II connection. These codes tell the tale of the systems monitored by your vehicle's emissions system, everything from fuel system status to engine and vehicle speed to the status of the vehicle's various O2 sensors. If there is an error with any of these parameters or if a value falls outside of a predetermined safe range, the vehicle will illuminate its Check Engine light.
The vehicle's computer is able to send all of this diagnostic information over the OBD-II connection to a connected diagnostic tool via PID along with special PIDs, known as trouble codes, that detail the issue. There are about 900 possible trouble codes in the OBD-II standard reporting on everything from fuel systems to emissions controls to transmission status.This makes it easy for a mechanic or emissions official to quickly diagnose an issue with a vehicle's engine and emissions equipment without hours of guessing and checking.… Read more