The Link: http://www.obdii.com/
All cars built since January 1, 1996 have OBD-II systems. Manufacturers started incorporating OBD-II in various models as early as 1994. Some early OBD-II cars were not 100% compliant. OBD-II signals are most often sought in response to a "Check Engine Light" appearing on the dashboard or driveability problems experienced with the vehicle. The data provided by OBD-II can often pinpoint the specific component that has malfunctioned, saving substantial time and cost compared to guess-and-replace repairs.
The service industry calls the Check Engine light on your dash an "MIL" or Malfunction Indicator Light. It shows three different types of signals. Occasional flashes show momentary malfunctions. It stays on if the problem is of a more serious nature, affecting the emissions output or safety of the vehicle. A constantly flashing MIL is a sign of a major problem which can cause serious damage if the engine is not stopped immediately. In all cases a "freeze frame" of all sensor readings at the time is recorded in the central computer of the vehicle.
Because of their investment in the equipment required, most repair shops charge a fee, some-times substantial, to attach the scanning equipment and diagnose problems using the OBD-II system signals. With the introduction of more economical and user friendly scanning devices, it is now practical for almost anyone to access OBD-II signals and use them for their own testing and repairs. (到AUTOZONE 或类似autoparts store,他们免费帮你scan code, 再对照你得shop manual 吧。 ebay经常可以买到很便宜的CD版)