I'm sure there is someone out there that is experiencing or has had this issue... I was driving home from a cruise last night and was on the highway and decided to activate the cruise control (not working). A few minutes later I noticed my speedo froze. when I slowed down and stopped it returned to 0. Starting driving again it went to 20, froze, then bounced up to 40 and stayed there. I know I was doing at least 60. No change again until I stopped. Any ideas where to start?

 

Okay... what does what? 25074709 (black box) is speed control and 25071437 (yellow box) is speed control buffer? The speedo on my 89' GTA auto is not working correctly, sticks at 20, 40, 60... sometimes just bounces. This all started after my cruise control stopped working. Not sure what box does what.

 

Hi GEmrsn, Yes you've got it right, the black box is the cruise control and the yellow box is the VSS buffer. I think two quick checks I'd do would be to run it with only the VSS buffer, leave the cruise module unplugged, and see if the speedometer still acts up. If yes, you should search out the procedure for checking the VSS signal coming from the transmission (good time to get a genuine GM Field Service Manual for your car). If the VSS pulses coming from the transmission are good, it very well could be that your VSS buffer has malfunctioned, but I'll bet there are further tests in the FSM* for that as well.

FSM* = genuine GM , not "Haynes", not "Chiltons", the real deal service manual from GM.....

 

Thanks, OrangeBird. I'll get into it this weekend and let you know what I can find out. I have an extra of each and a new sending unit for the tranny...

 

That's great that you've got the FSM, I'll be watching to see what you find