Re: 92 Accord Transmission Won't shift
If D4 light is always on...even in park...that's your signal for a tranny prob. From what I understand, the speed sensor only affects downshifting. I'm willing to bet that it's a bad TCU. They're known for leaking capacitators. Try disconnecting your battery or pulling your radio/backup fuse for a few minutes. If that helps (would only be temporarily) it's your TCU.
As poorman mentioned...jumping your connector should make the D4 light flash...counting will give you the related trouble code(s). If you do some research there's also a couple of checks you can do while driving and shutting off the car over a certain speed to see if that temporarily fixes the prob, but I can't quite recall the actual procedure and that sounds kinda shady to me personally. Good luck.