Gas cap was loose on RX 400h. Engine light came on. How do I reset the check engine light short of disconnecting the battery after tightening the cap.

I would...tighten the cap. If that is the probem, it will eventually go out.

ok. I reset the gas cap and see what happens. thanks.

Yeah, after so many start cycles if the ecm doesnt detect anything, it will go out. my recommendation is to buy an actron (or similar) code scanner/reader. Not a whole lot of money, and definitely worth it.