Whirlpool washer Cabrio WTW6600SB1

Cabrio F51 Fault (Stored Fault Code F51) The Cabrio's F51 fault code flashes on the washing machine's display when there is a motor rotor position sensor (RPS) failure.
Check for good contact at the control Board and at the RPS. Sometimes disconnecting and reconnecting the RPS plug connection several times will clean off corrosion that may be affecting the contacts.

Here is an earlier Fixya answer addressing the query:

Whirlpool cabrio error code f51 what does it mean

Sensor is item 20 below. Clean it.

It generally means a problem with the water supply. Here is a link to all the codes: Whirlpool Cabrio Washer Fault Codes

If you have to dig into the machine to repair, utube can be helpful:

Cleaning washer filter


Whirlpool Washer Diagnostic Repair F1 Error Code WTW6400SW2

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.

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.

It means you have a control board fault. Call Whirlpool and tell them the fault you are getting and see if it's recalled. There's a good chance. You can install yourself or have and appliance tech do it.

Rich
Western Appliance Repair Meridian

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

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.

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

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.
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speed sensor and a control board

upgrade rps sensor and it will eliminate the problem

Its the Rotor Position Sensor very easy solution!!!chat with me online and ill step you through it save up to $65 (my in-home rate in florida is $75!!!!!!!)