If it makes you feel any better mine has been doing the same thing for about three months now. On for a couple of days off for a week, on for a day, off for a week again. I took it to the dealer to have it looked at, and they told me something in the charging system gave off a bogus error causing the Check Engine Light to come on. (Idiots) I have noticed that when it rains hard, or when I power wash the car it sometimes comes on after that, but it really seems to be completely random !?!?! I sometimes will disconnect the positive battery cable for about twenty minutes or so then put it back on, I will get a BAS (I think it is) light come on, then it will go away very shortly after start up, and magically the Check Engine Light goes away.

BTW, I was not charged for the test on the car at the dealer, but it was still under warrenty at the time.