I'm going to keep this as short as I can.
OBD II was mandated & implemented by 1996. Some mfg.'s started a little sooner.
The purpose of OBD II was, to establish somewhat of a standard for all vehicle mfg.'s.
Also, OBD II is much more sophisticated than OBD I, the idea is to minimize exhaust emissions even more than before.
From a tuning perspective, it is very difficult to " fool " OBD II.
Even some minor changes/faults can trigger the Check Engine Light ( loose gasoline filler cap, etc. ).
Hope this is what you are looking for.
