pudhonda

I have one of those notorious flashing "D"s on the console of my 2003 Odyssey. Just to get some preliminary stuff out of the way: I changed the fluid AND the filter last year (or maybe the year after) using Honda fluid. The color and level on the fluid are good and the tranny and engine are running fine without problems. When I turn the engine off and back on the "D" stops flashing. I've seen elsewhere references to computer codes that people are getting with readers, telling them that one of the pressure switches is malfunctioning, and they've fixed the problem simply replacing the switch. Problem is I'm not getting any codes when I scan my computer. Is there a trick of some kind to pulling trany codes? Or do I need a special reader to get at them?

Thanks in advance.