Honda-tech has a post on checking the tranny and engine codes. Hope this helps. http://www.honda-tech.com/zerothread?id=962851&uid=999378256&dir=1&postid=11122854 This site looks like it's just about right, with pictures and everything :) http://www.dhost.info/accordinfo/howto/cel.html
When the light comes on, your car has stored a trouble code. I would have the codes extracted(PEP BOYS/AUTO ZONE) to determine the problem.Sometimes it can be minor, but there can be 30+ different codes.