KitchenAid upper arm not working

Our Kitchen Aid no longer washes the dishes in the upper rack. We’re assuming the arm has quit working, but could it be something else? Maybe a pump? The dishes on the bottom rack still come clean, although we do get some detergent residue on top of the glasses.

Thanks

I have Kitchenaid KUDMO1t JBLO and the same thing happened. Thinking that the pump wasn’t getting enough water to get up to the top spinner, I removed the lower arm and cleanout out everything I could, but it didn’t help. Had to call for repair man. He replaced the “Chopper Assembly” which includes a screen. Could have done it myself if I could have figured how to remove the “Inlet Protector”. Cost $150.00 total