Speedo / Cruise control out of control

Catman59 · June 13, 2005

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 ??????? I was pulling my boat yesterday.50 its OK , but after that things start to go wild.

GM-Tech · June 13, 2005

Speed sensor or related wiring, but I can't see why it would be okay up to 50 mph.

Catman59 · June 15, 2005

Dealer has it again. Bad computer...........is the cause

Catman59 · June 17, 2005

Well its on its 4th day at the dealership. Not the wiring ,not the computer .Even checked the ring in the transfer case........Now they are headed into ABS.............

GM-Tech · June 17, 2005

Well its on its 4th day at the dealership. Not the wiring ,not the computer .Even checked the ring in the transfer case........Now they are headed into ABS.............

<{POST_SNAPBACK}>

?? ABS is not at all related to the speedometer or cruise control. We've had LOTS of cluster problems (speedo's jumping around, sticking at one speed) but I don't see that affecting the cruise... though I'd need to look at schematics.

Catman59 · June 17, 2005

The verdict is finally in..........Transmission control computer. They tried one out of another truck and it is fine. As a Tech for Cat myself , I know that wiring can do strange things. I also know without the right diagnostic equipment....that you are better off leaving it alone !

GM-Tech · June 17, 2005

I forgot all about the separate TCM for the Allison. Almost zero problems with those.

Catman59 · June 18, 2005

Thats what they said too..............But Its mine and I seem to attract things like that !!!!! I've been a service tech for CAT for 15 years, so I understand troubleshooting too !