The OBD-II protocol along with a Computer Area Network (CAN) protocol is still in effect as of this writing (October, 2013). This protocol, when adopted in 1996 was another giant step forward for the aftermarket auto industry because one scantool could be used to service ANY car that rolled into the shop. This protocol now specifies that all cars and light trucks will communicate with the same OBD-II scan tool.
In North America the protocol is called OBD-II. In 1996 OBD-II was adopted by every car manufacturer who sells vehicles in North America and the European NATO countries. This means, for example, a Subaru scan tool will only work on a Subaru. The car manufacturers outside of North America adopted brand specific diagnostic protocols. This was a big step forward for aftermarket repair shops who work on many different brands of vehicles. This protocol allowed all vehicles in the USA & Canada to use the same scan tool to diagnose the vehicle.
The North American Auto Industry and SAE (Society of Automotive Engineers) adopted a standard fault code protocol, connector configuration and ECM software protocol in the early 1980's and called it OBD-I (On Board Diagnostics, level 1). The aftermarket soon started selling "code readers" that could also read and erase the fault codes stored on the ECM. Again, assembly plant technicians and dealer technicians could plug in a OEM scan tool and diagnose the vehicle. When a particular engine control failure occurred, the appropriate code was stored in the memory of the ECM. Every type of engine and transmission control failure that could be created in the test lab was assigned a fault code. If any of the signals the ECM should be receiving suddenly stop transmitting or are out of an acceptable range, the ECM loges a fault event and assigns a specific code to the type of failure encountered. It received information from the powertrain from sensors that monitored the engine while it was running. The electronic control module electronically controlled vital parts of the engine and transmission through the adjustment of actuators and solenoids. On early vehicles built in the 1980's, by plugging in the scan tool connector to a connector located under the vehicle's dashboard, the scan tool could communicate with the vehicle electronic control module. Just after GM started using in-house scan tools, most other manufacturers followed suit and developed their own scanners and software that resided in the vehicle electronic control module (ECM). A particular fault might be "no signal from the crankshaft position sensor".
The fault code was a short series of numbers and letters (P1021) that corresponded to a fault mode within the engine or transmission. The basis of early electronic vehicle powertrain diagnostics strategy was the fault code. The automotive industry continually improved the scan tool every year and then required dealership technicians to use scan tools to diagnose problems within the powertrain. These scan tools generally used a blinking light ofraudible sound to alert the user to a problem. These scan tools were developed to assist the GM technicians and engineers in the factory to diagnose engine related problems with cars just assembled on the assembly line. Automotive OBD-I Diagnostic ScanTools were developed in the 1970's by technicians at General Motors Corporation.