It's the crank sensor!
Join Date: Nov 2007
Location: Central Minnesota
As you mentioned, 97 was the "transition" year where early models could retrieve codes with the key-on, key-off method, but later builds in that year could not. Anything post 97 cannot use that technique.
As mentioned, best bet if you have a code is to get a code reader or a scan tool as the key-on key off method doesn't retrieve the entire 4 digit code that is necessary for best diagnosis.
Hopefully your light/code won't return. If it does, you know what to do. As the check engine light was on, you have "stored codes" to retrieve, regardless of whether the light is still on.
99 Cherokee, 4.0 AW4, NP242
Past Jeeps: 49 Willys, 81 Scrambler, 88 Comanche
Without "data", all you have is an opinion!