i have a 08 impala ls that the speedometer acts up when its wet outside, it goes up and down untill i see a 107 mpg message then car cuts off, all that happens while stopped on D, i have swapped the speed sensor on the tranny but i still have that issue

any ideas why?

 

I would get it scanned for any codes that maybe available.

 

i did scan have it scanned but nothing comes up, this thing got me scratching my head

 

WOW, I'm scratching my head too! Does your scanner have the ability to display live data? You could watch the speed on the scanner and see if it goes up and down like on the instrument panel. Maybe try to narrow things down a bit and see if the jumping speed is due to bad incoming data to the cluster.

 

Could be a bad ground, Look for and clean all ground connections, battery and any ground straps.

 

I will check that next, its possible but that still doesn't explain why it only happens when wet
thanks

 

yes live data shows the same thing