I also had the F28 error code and I finally figured out that there was a tiny amount of corrosion on the metal leads in the end of the wiring harness for the 3 blue wires that connect from the CCU to the MCU I popped the 3 blue wires wiring harness out of the MCU, sanded lightly on the metal leads in the harness, popped it back in and the washer works great again!