PF flashing on display

My Frigidaire Dishwasher will run for about 3-4 mins. and then display PF.
So I ran the Service Test by pressing Sanitize and Start/Cancel buttons at the same time. After the test finished the display read Clean with an S under it. So I opened the door and then I closed it, and the Air Dry & Hi-Temp Wash LED’s are blinking and the display is flashing PF. How can I get my dishwasher working correctly again?