I have a Kitchen Aid Undercounter Dishwasher. About 4 years old.
All of a sudden, I have water coming out of the air vent on top of my
counter when the dishwasher drains.
I have checked the traps, the clean out under the sink, the disposal,
and even taken off the air vent hose and made sure it was clear going
to the disposal and going back to the white/clear drain hose coming from
the dishwasher. And the paperwork that was left with the dishwasher
when it was purchased tells me nothing.
Any ideas would be welcomed.
Thanks,
Dan 
This sounds more like a restricted drain than a dishwasher problem. As long as your not oversoaping, I don’t think there’s a problem with the unit. =]
Could be a dirty air gap (not sealing correctly) or it needs replacing.
You could disconnect the drain at the house plumbing and drain it into a pail/
Just be sure to hold it securely and put a towel/rag over the top so it does not splash all over.
then if the drain hose from the air gap to the house drain is clear, the problem will be with the gap itself.