Speedometer Failure

Hi Pontiac owners, Pls help me to retify my Pontiac Grandprix LE 90. I'm facing some problems with it. First of all the speedometer and the engine t/p/m meter runs faster then the reality. Where can I search for this to retify the failure. Please let me know what to start with. Got some more to ask about other things. I been own this vehicle since it was new.

Pontiac Grand Prix! Please Help me!
I got problems with the Dashboard meters. The meters run faster than the car. Where can I retify the fault or what shall I do. I own this car since 1990. One owner since it was new. I'm from Sweden. I got some other failure as well to ask. Pls asnwer this first!
Thanks Nic.

To start it would help to post the transmission you have and engine size.

You should have a 4 speed autotransaxle TH440-T4 aka 4T60 GM RPO code ME9. Check the SPID data label to verify.

So are you saying your speedometer is out of calibration. How far is it off? By how many miles or kph? Are the wheels and tires stock size?

The signal for the speedometer is taken off the vehicle speed sensor - VSS.

Also, is 4th gear - overdrive working?