overdrive mystery on 98xj

Last night check engine light came followed by the tranny not shifting to overdrive. No noises, vibrations etc. Later on in the evening, check engine light still on and tranny shifting just fine. Anyone have any ideas? Could be there be a relationship between these two problems?
TIA
Brian

My first thought is a TPS. Because I had a similar problem on an older XJ and it would not shift out of 2nd gear. But thats a long shot. Just a guess.