I own a 1999 Base Cadillac Deville and I have a problem that has plagued me for 21 years. And no one, including Cadillac has resolved it. At speeds below 60 mph my speedometer is steady AND accurate. However, when I accelerate over 60 mph the speedometer is erratic and vascillates 5-10 mph under and over my actual speed. Of course, this disconnects the cruise control and it is inop until the car is shutdown for a considerable period of time. I've replaced the VSS speed sensor more than once and it currently has the Delco OE sensor installed. A few years ago I replaced the engine and transmission and the persistent problem remained. I occasionally get a PCM CCode of P0503 for a faulty VSS. There are no other symptoms codes. Could my wiring be grounding?
Please help! I've exhausted all ideas...
Thanks!
Ron