OBD is an acronym for "On Board Diagnostics". OBD-I was version 1, OBD-II is version 2.
It is an industry-standard method of communicating with the onboard engine computer. It was created so that ECUs from different manufacturers would have a standardized communication protocol instead of several different proprietary versions.
Sometimes pre-OBD cars (such as 1G DSMs) are referred to as OBD-I cars. This is not accurate, since they use the ALDL interface. 1995 cars might be OBD-I rather than OBD-II, but since most OBD tools support both I and II the difference is usually not important.
There are actually three different possible interfaces within the OBD-II standard: PMW, ISO, and PMZ. [So much for standardization....] All 2G DSM's use the ISO version of the interface, so any diagnostic equipment used must also support the ISO version of OBD-II.
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