F51 is an RPS error, but can be caused by several things. First try spinning the basket by hand, make sure it moves freely. If your getting the error immediately upon start up there could be clothing stuck between the tub and basket. Also the rotor could be loose (I have seen this many times on these units). You would need a garbage disposal wrench or allen wrench to tighten. Check these things before tearing it apart or replacing anything.