08 M8 speedo help

[Colten KM8]

on my 08 M8 the speedo quit working. the RPM and Altitude still come up but it wont show the speed im going. when i start the sled the needle goes to the top of the guage then comes down like it does on all M-series but when im goin across a field or in the mountians it wont show the speed im goin.Anything i can check?

 

[tavis43]

mine did the same turnned out to be a broken wire in the harness, also the dealer said the sensors get dirty and fail.