Originally Posted by Asahi
There were revisions to OBD2 as well. OBD2a existed until 1998 and then OBD2b came out. Obviously whatever changes came out were small enough to do be a different version. But ti did warrant new wiring harnesses.
Those are designations relating to changes Honda made to its wiring and really have nothing to do with the actual on board diagnostics of the car. There's no US DOT requirement for OBD-IIa or b or any of that stuff. That doesn't mean that carmakers can't change their wiring specs, it's just that the current diagnostic spec as required by the gov't is still OBD-II.