Do you know how to check engine codes? If you do, then act as if you were checking on a CEL and see if your D4 light blinks when you are doing it. If it does, write down the sequence. There should be a site somewhere (you can probably google it) that has a listing of Auto Tranny codes. But yeah, your D4 light can act as a CEL for tranny trouble, but I'm not sure that was what it was doing in your case.