A malfunctioning appliance can be challenging. So many error codes, what do they mean? I find a good starting point is the owner's manual, it usually has the codes for your washer and what to do next. I also found some information about this code on two appliance web sites. They may be helpful while you wait for the expert answer. I attached the links below. Hope this helps!
The F6 error code indicates a drive motor tachometer error. On something like this you will need to access the motor control board & use a meter to check the tach. In the wiring diagram provided place your meter leads across pins 4 & 5 of the motor with the connector disconnected to check the resistance of the motor tach. You should read approximate 119 ohms. If the motor tach checks good I recommend replacing the motor control board. If the tach checks open you need to check the harness to & from the motor & if the harness is good replace the motor.