Speedometer is stuck on 80 even when iam going 10 mph. some times it reads lower than 80 and sometimes higher but its not functioning

maby the cluster smack the dashborard with your hand while your moving and see if it reads ok

they had a lot speedometer clutster problem, maybe even covered under a warranty, contact the dealer.

sounds like you have a bad ground in your dash where your gauges are located should come out as cluster check for loose wire!

The speed sensor is malfunctioning on the transmission.I would not fix it as a result of the age of the car.Simply use a GPS for a more accurate speed

Need scan tool to see what speed is showing in the body control module. If that speed is correct, then the instrument cluster is bad

Many cars have an error on the speed indicated. 10% sounds quite high, next time you buy tyres go for one size bigger or the next profile up, eg, if you are using 70 series go to 75 or 80. That will sort your problem out and you will get better fuel consumption. You can have the speedo calibrated but I would thing that the cost or effort wonuldn't justify the result.

You need to take your vehicle in and get a calibration done on it. Hope this helps

Passenger side of car on top of the very end of the transaxle...two 10 mm bolts to remove.

There was a recent class action law suit settled with GM for this exact problem. You can google gm speedometer lawsuit and get lots of information. Unforutunately for most people I think the warranty was limited to 7 years and 70,000 miles. Which isn't a lot of miles for most people.

If you car isn't covered by the warranty there is a way to "reset" the speedometer.

You can turn the ignition slowly like you are going to start the engine. There is a very small "dead" space where you will see your guage lights go off.

What you want to do is cycle the ignition switch from off to that dead space. Each time you do it your stuck speedometer will move towards zero about 10 mph. So if its stuck on 40 you will have to cycle it at least 4 times.

At first you will probably actually hit the ignition and the engine will try to start.....just release it and try it again.

I know this because I have a 04 avalanche with 80,0000 miles and it has this problem about twice a month.

I took it in for repairs.