CEL came on, but I scanned it without a code...

Like the title says, I was driving normally, and I shifted into fourth or fifth smoothly and the CEL pops on. I take it out of gear and pull into a strip mall, pull out my Diablo and check the code, it says no codes found.

I clear them and baby the car home about an hour ago. Just went out and started it and let it run, and no CEL came on..WTF????