My speedo and tach along with all the other Randomly Start bouncing Crazy up and down or in circles and where the miles Read it says Error? Any Ideas Other than that the Truck runs Good.. The Truck Used to have Onstar but was removed and the TRanny has been Professionally Replaced... Im trying to sell This Truck but have no idea what would cause everything to Randomly Tweak out. Sometimes it works ok sometimes it Tweaks The Miles Always says ERROR. THanks Everyone

 

Make sure you have a good battery / connection at the terminals. Rid of any corrosion on them as well. You can try to look for problems in your fuse box also. Other than that, I have never had this problem before "on a blazer". Check out the search button on the forum's main page. I'm sure there is a thread there that will help you find your problem. Good Luck!

 

my 1998 blazer / speedo and tach quits , hit a bump lights all come on , they work again ???

 

I've read somewhere that the rear VSS (Vehicle Speed Sensor) could be the issue, at least from what I remember the symptoms sound quite similar.