What's the best tag to use for questions with a specific CEL (Check Engine Light) code? I've seen various terms for them on other forums and sites.
OBD-II means something specific: it's a (US) government standard that started in 1996. The other terms are the same concept, but more generic. If someone says OBD-I, then I know they are talking about pre-96. If they say OBD/CEL/Error code/etc, it's ambiguous.
Before the standardization in '96, Honda's code for misfire may have been X102, and Ford's code for misfire may have been 0x35. The OBD-II code for random misfire is P0300 whether it is a Ford or Honda.
Usually manufacturers don't want a different engine computer for every country, so I believe OBD-II is known around the world.
I'm not sure how useful OBD-II is as a tag. I suppose someone may want to peruse and answer OBD-II specific questions. The actual code (e.g. P0300) should work well as a tag. Over time, code P0300 may have 100 answers, and a professional could see what all diagnostic steps were taken for a wide range of vehicles for that specific code.
MIL - Malfunction Indicator Lamp is the official acronym to refer to the check engine light.
I cannot find the reference for that right now and will edit the question with it later. It may only be a USA standardization, but I am pretty sure it's international.