90 Grand Prix issue... gauge cluster issue

Hey guys! I’m currently helping a friend fix up his old ladies car so she can have something decent to roll around in. So far we have fixed roughly 90% of all the issues. Theirs just one thing that im not 100% sure about. It’s a 1990 Pontiac Grand Prix 3.1 v6 auto coupe. SE(I think). The issue that im having is the gauge cluster! Everything works on it like normal except the tach and speedo. You can be doing 20ish and the speedo will state your going 120mph! Also it “idles” at 5.5k. I know it doesn’t due to the sound and my scan tool. Any ideas what this issue could be? All fuses are good, no codes. Also when you come to a stop the speedo reads 0mph.


PS: The tach or the speedo always apear to read like 5 times of what the actual speed or rpms are.

Edit: The car runs, drives, and shifts fine also

Sounds like you got it backwards, the rpm is 1200 and the speed is 55mph.
lol

You have a ground issue on the dash I believe. Those cars will do that, check the chassis ground on the PCM to be sure it's not corroded.

If that's not it then try adding a ground on the transmision and see if it'll fluctuate when you tap it to ground by hand.

Forgot to mention that the low gas light is always on. The gas gauge works fine other then the light beign on constantly and the check gauges light is lit up? Still could be a bad ground?