Jason Ubertek at K.C.Canary addressed this:
<font color="green"> Short, long, long, short or .--. is indeed the fault code for the mfwd sensor . If you have cruise control it will not function. The flywheel speed sensor is also the same part # as the mfwd sensor. So in my opinion the flywheel speed sensor could possibly fail, Their is an internal wiring problem inside certain speed sensors. Deere has corrected the problem with a fix as fail . This doesnt mean that everybody with e-hydros has to worry, not everybody will experience this. contact your dealer. The kit consist of both the mfwd and flywheel sensors and take about 5 minutes to install. </font>
When I had this, restarting the tractor resoved it.....