I did have that big hose off when I changed the pump some months ago. I cleaned it out real good. There were a few screws,pennies etc and slime in it. There wasn't a filter though. I'll check it out when I have it off again.Also this machine doesn't have any kind of lcd or digital readout so I don't see how I could see any codes. I guess it's too old. Unfortunately I heard from another that the rear outer tub bearing sounded loud like it's about to go out which sounded serious. Anyway will take a chance with the cheapest pump I could find from a seller with very good ratings and hope it can go for a while longer. Thanks for the advice.
Have you cleaned the filter for the pump, In older Frigidaire's they are in the big hose from tub, to pump. You may have to disassemble to get the front off, to get to pump, (if it has full front.) Some models has a split bottom and you can access the pump from the lower section. Be prepared with a wet vac if inside doing repair.
a weak pump can also be a problem. Runs ok but not at peak Gallons per Hour. Have a high water level over the spin kick in level.
I recently did a filter clean job, and ran a load and the unit would just rotate back and forth like mentioned in post above. I swapped out a unit I had with my customer.
Back at shop the unit did same thing. Then I ran a diagnostic check. Doing this cleared the problem. You HAVe to learn How to read the codes, and do these checks. This may not fix yours but worth a try. Water level and lid switch are the right ballpark, but you again must learn proper testing, and wire checking, including wires that are in connectors, look good but aint.