The F51 fault code on your Cabrio washer indicates that the control board is not sensing the proper drive motor spin. To clear the fault code, press the Pause/Cancel button.
First, I recommend checking the issues discussed in the attached link:
In addition to the above tips, check the installation of the drain line. Make sure that the drain hose is not stuck way down the stand pipe. This can cause siphoning of fill water which will inhibit proper motor rotation.
Check to see if the wash basket spins freely. If it does not, you may have an item of clothing stuck between the outer tub and the inner basket. This restriction in rotation will also cause an F51 fault code.
If these tips do not help you resolve the F51 problem, then you probably have a component failure. Possible failures include: wire harness or wire connection problem between the machine control and the RPS sensor (Rotor Position Sensor), a failed RPS sensor, a failed drive motor, and a failed machine control board. You will probably need a technician to diagnose and repair one of these component failures in your washer.