If you have an air vent at the top of your sink check that for clogs thats common or take the hose off underneath the sink and take a shop vac to it and make sure the pipe/disposal at the sink isn't clogged. Best way to test it is fill it with water and take your drain pipe from the dishwasher and put it in a bucket and hit cancel drain that'll tell you where the problem is if it's in the hose or at the sink. Also some of those drain hoses have a flap inside the motor connection area that prevents the water from backflowing into the unit. Sometimes those flaps get stuck or actually break off and get clogged in the drain hose. Good luck..........oh and make sure you have 120v at the drain pump while it's running if you don't i'd suspect a main board issue.