Three times now in the last 200 miles my check engine light has come on for about 30 seconds then turned off. Each time was when I was moving at a constant speed and I could feel no difference in the way it ran when the light switched on or off. It feels the same it always has. It might be burning a bit more gas than before but that could just be my imagination.

I'm not quite sure where to start here. As far as I know none of the sensors have been changed in at least the last 80k miles. It currently has 240k miles on the original engine.

Any suggestions?