Speedometer Gone Wild !!!!!!

[Catman59]

Hi Guys.........I have been lurking here for a while and thought Id join up now that I have a problem to discuss. I have an 01 2500HD with 8.1 and Allison. I noticed the last time I drove it that the cruise was real jumpy and acting up. It was late and dark , I kicked it off and it started back up and worked fine. Tonite I hit the cruise and it went wild , I also noticed the speedo was smooth to about 40 and cruise was OK. As soon as I got to 55 the speedo started moving from 40 -70 and jumping wildly. Then the ABS light came on , followed by the brake light. Nothing in the message center. I stopped and reset the key and it was OK to about 40 then went nuts again. Any help PLEASE ???????

[Haulin' 8.1]

Replace the rear wheel speed sensor, it's on top of the axle housing.

 

Vernon

[Catman59]

Its been at GM shop all day. No codes , only 1 was mass air sensor. I put an aftermarket one on and when I started it , I forgot to plug it in , so that was the code. Speed sensor was OK. It is very intermittant and they cant even get it to do it very often . It seems to be a cruise problem. There is a communication problem from cruise module to throttle body. Im going to use it tomorrow.......pull the boat and see what happens.

[working on it]

I have been lurking around here as well, and my first problem (disregarding the always present intermediate shaft wobble) to report is also the speedo. Last week, at 48k miles, I was driving home after a really long day, not paying full attention, and started passing everything in sight. I was accelerating to 55, but by the time I had reached 40 mph I knew to look at the tach...much too high a reading. I slowed to match traffic and made a mental note to compare mph/rpm readings when home. When parked the gauge needle was about 1/2" below 0.The mileage traveled did not vary from normal though.I forget what they were now, but the mph readings I jotted down showed that the speedometer was reading 80% low. The next morning I checked for loose connections etc., found none, climbed in and went around the block (5 miles). Same thing. But when I turned the key to off, the speedo needle went to zero. Another trip around the block; everything was back to normal.However, during the last few days it has occurred three more times.And, twice, the speedo head itself started growling like there was a bad cable driven gear inside.Seems that the driven gear inside the head is slipping).I called the dealer and they will repair/replace the head.(And while it's in there, the hydroboost check-up,the tail gate cables, and the intermediate steering shaft done as well....).