While OBD started life as a simple diagnostic tool for checking emissions, today's OBD-II is much more sophisticated. Again, its a matter of adopting standards so thing can 'speak' the same digital language. All computers contains a UART chip to manage the serial ports, and to send and receive the data in and out over these ports. This is a computer component that handles asynchronous serial communication. Signaling between the OBD-II connector and the various computer systems in the MINi are by way of a UART, pronounced u-art, and short for universal asynchronous receiver-transmitter. This protocol has a data rate of 10.4 kbaud, and is similar to a standard RS-232 connection.
If the vehicle has automatic transmission there is also connection to the Gearbox Interface Unit. On the MINI, the connection is a part of the D-Bus and has direct connections via this bus into the Engine Control Module, the Anti-Locking Brake System, the Electro-Hydraulic Steering, the Automatic Stability Control module and the Dynamic Stability Control system if fitted. Here is a diagram of all of the possible pin-outs on a generic OBD connector. Each of these define the communications protocol, or the type of data signals that carry the information on the OBD connector. A high level view of the field is as follows: GM cars and light trucks use SAE J1850 using variable pulse width modulation or VPWM, Chrysler, all European - including MINI - and most Asian vehicles use ISO 9141 protocols and Fords use SAE J1850 pulse width modulation PWM. Still not completely common across all types, OBD-II has three different communications protocols. Later, OBD-II added another layer of connectivity between the vehicle's on-board computer and peripheral test equipment for fault location and analysis. So between the SAE and CARB and the automobile manufacturers, a standard was adopted that provided a common connector on all vehicles and a set of standardized tests that could be run to make certain that the vehicle was meeting the manufacturer's standards. Starting in 1996, all cars sold in California had to provide some basic engine diagnostics to make certain that they met the ever increasing demands of the California Air Resources Board or CARB standards. About this time the Society of Automotive Engineers recommended a standard connector and a number of standardized test signals.
In the late 80's, with California pushing hard for some standardization of emission controls, the preliminary OBD standard was adopted by manufacturers to make sure that vehicles' emission were not exceeding guidelines established to meet the Clean Air Act. The On board Diagnostics, or OBD, is yet another computer system built into all vehicles since the late 80s to assist in the monitoring of the engines performance in the interest of emissions monitoring.
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