PF is a fault message indicating that the motor has been drawing more amps than the current limit setting entered into the VFD. To clear this fault, the operator must issue a stop command from the keypad. The grinder will not restart unless the fault condition has been corrected.
The warning message CL is the precursor to PF. When the grinder is operated under a CL warning message for multiple seconds the PF fault will disable the grinder. See CL solution article.