My discharge would not empty after a wash cycle and I always had gross gray water left in the bottom approx 3" deep?
After doing the obvious things of checking the simp for garbage, and checking that the discharge hose wasn't blocked, I removed my discharge pump ( not too hard to do) and tested. My pump which did run and turn the impeller. However, the pump evidently had weakened with time and weakened and could no longer pump the waste water up hill to the "T" connection under the sink.
A new $65 pump remedied the situation and saved me from buying a new $600 dishwasher! The install of the new pump took approximately 1 hour. The only tools required were some screwdrivers to remove the door panel (for working room) and the valance at the bottom of the machhine and remove a hose clamp; everything else came apart with locking plastic tabs.