My girlfriends' '98 Ford Escort had the same problem (suprisingly, it also has an electronically-controlled transmission). Here's a quick way to make sure that is the problem. Just disconnect the transmission speed sensor, then start up the car and watch for any additional codes. If no additional codes appear, you can be pretty darn positive it is indeed the part you suspect. However, if unplugging the part in question causes another code to appear, then you know that the part was working, and the cause is something else. Try it out, but this method does take some time to do. Good luck!