What is OBD1

OBD1 is the standard for On-board diagnostics, which is applied to cars made for the state of California in America from 1988 to control vehicle emissions in that state. All cars marketed for this area had to be OBD1 equipped to detect engine problems and display error codes. Despite being a California state standard, OBD1 can be found on many GM and Ford cars made in the early 1990s. However, unlike the later OBD2 standard, OBD1 was not standardized between car manufacturers. This meant that an OBD1 scan tool often only works for one car make. Also, the error codes themselves are not standardized. For example, a Ford with the same engine problem as a Toyota can display a completely different error code in the OBD1 era.

What the OBD1 connection in the car looks like differs per car manufacturer. At the time, the car manufacturer was allowed to choose what kind of connection they used. There was no universal connection for all car manufacturers and no fixed procedure for reading out a car, or no standard. Many trouble codes in the OBD1 era could be found by analyzing the flashing Check Engine Light by connecting certain pins together in the diagnostic port.