odd tach and speedometer

my grandmothers '06 Buick LeSabre has started having problems with the tach and speedometer. only 37k miles on it. the tach does not display correctly, and the speedometer is not accurate and sometimes does not work at all. any suggestions?

Verify make and model, the Lesabre ended in 2005. Regardless, if your car is a 2006 Buick, check your local dealer for warranty. The 2006 model year had an extended bumper to bumper warranty. If your car is the 2005 or older series then your warranty would be expired. GM dealers have the ability to do a "sweep test" which can reset your instrument cluster and determine if the instrument cluster needs to be replaced or not. If so, there are remanufactured clusters available from various manufacturers.