It just has whatever kind of diagnostic and electrical systems that Nissan wanted.
OBD-2 is simply the standardization of on board diagnostic controls and engine function in the US, mainly for emmisions control.
Before 1996 there was no standards for the controls of diagnostic systems and so therefore no OBD I. Calling your car that is from before 1996 "OBD I" is common way to associate your ECU type but is not the correct way.
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