Hi Doc!
You know? If I had to postulate an educated guess, I'd wager that your dishwasher's (DW) drain hose isn't hooked up properly under the sink. When it's not hooked up right, water from the sink will siphon down into the DW making you
think that there's a problem with the DW when in reality the problem is elsewhere. Kinda tricky, huh?
Anyway... I put together some photo's that show the incorrect installation and the correct installation of DW drain hoses. Check it out.
The downward sloping hose allows water from the sink to go to the DW.
The "loop" (actually called a "vacuum break") won't allow water to go to your DW.
Here's a schema of the layout...
So the drain hose from the DW always has to loop upwards to keep gravity from weilding its' wicked hand and drawing water down to the inner most depths of your dishwasher.
So, that's the first thing to check, Doc. (<---- that was my Uncle's name, btw. He owned and operated a microwave repair shop back in the late 70's.) If you find the hose under the sink looks like the first pic, just loosen the clamp, pull as much slack from the DW as you can, form a loop like in pic #2, tighten the clamp (to hold it in place) then tie off the hose to a stationary location (like the hot or cold line feeding your faucet)
There ya go! Fixed! Ain't it cool? How easy was that? What about 20 minutes? Maybe less? All you needed was a 5/16" nutdriver and some tape! Too cool.
Don't forget to rate me, OK? My self esteem is counting on you.
Oh! If you find that the drain is properly installed, let me know. We'll go deeper into the solution, OK?
SG