Chrysler Repair: Speedometer Erratic/Trans goes into limp mode, plymouth grand voyager, grand voyager

Question
Roland,  I have a question on a fault on my speedometer in my 96 Plymouth Grand Voyager.  It starts fine but when I get to 30-40 miles per hour and let off the gas the speedometer bounces from 10 to 50 miles per hour.  The Tach doesn't reflect this move.  The transmission then goes into limp home mode (wont get out of 2nd gear).  It clears if I restart the van.  It doesn't do this all the time, seems to happen more on cold mornings.  I tried looking at the codes after this happens (on-off-on-off-on ignition) and get nothing.  I am thinking intermittent speed sensor.  Before I take it in to get looked at, I would like a second opinion.  Thanks

Answer
Hi Ron,
I believe you have the correct diagnosis. The Speed Sensor is necessary for both the speedo and the transmission controller to properly operate. The self-readout feature is not designed to get codes from the transmission system so that is consistent with what you observed. A readout with a plug-in diagnostic box would no doubt give you the speedo fault code, if I am not mistaken.  
The sensor is located on the side of the trans that faces the front of the van, near the very end of the power train and has a light green/white wire and dark blue/black wire. You can replace it yourself and save the labor charges if you wish.
Roland