I believe I had the exact same Check Engine light. It would come on for most of a year once a day then go out, and the dealer couldn't point out exactly what was causing it. Eventually, my fuel sensor relay went out and caused my car not to start or to stop mid-drive periodically as if it was running out of fuel. I dropped a little solder on a small crack on one of the solder joints on the fuel relay. The car started right away. This happend about two weeks ago and I haven't had the Check Engine light come on since and the car has been terrific.

Don't know if this sounds like what you're dealing with but I know my check engine light worried me for a while and it was my relay.