speed odometer not working

I have a 2004 Impala 54000 miles. My speed odometer is not working properly. It will start working but when I stop it will not go back down to 0. When I begin to go again it will just start where it was. It has went all the way around, and to get it back to 0 I have to keep turning the swith on and off. My odometer is still programing milage though. Any info is greatly appreciated.