Do-It-Yourself Story

First, I was quoted $139 plus parts to diagnose and fix the machine. Probably not unfair, but I'm cheap -- so I checked YouTube and there was a very nice diagnostic video there that made me feel quite confident in figuring out what was wrong. I ordered this recommended part (the water-level sensor), which was delivered very fast (~2 days). Then I pulled the machine, turned it off at the breaker, unscrewed two screws holding on the thin metal left-side panel, removed that to expose the water control system, figured out how to use a screwdriver to release the water-level sensor, unplugged it, cleaned it, and replaced it. And ... the machine worked. So I'm keeping this lovely new part as a spare -- and well worth the price, since as several people mentioned, this DW design is very dubious. Machine now works perfectly, and as a bonus, the water level is now correctly maintained (apparently, it was being incorrectly maintained before due to gunk in the sensor) so the dishes are getting washed completely clean instead of sometimes ending up not-quite-clean. Very satisfied customer.