G.W.
I had the same problem, but it was a much older dishwasher. The repairman took the drain apart and found a rubber valve from a sippy cup and some broken glass. Guess the glass was from a broken dish, but the valve still amazes me. We don't use that kind of cup, so that thing had been in there since the previous owners had lived there--over 3 years! So, my only advice is to get as deep into the drain as you can without damaging something and see if you have a stray piece of something stuck there. Good luck!