Dishwasher is backing up into double sink while running. How can I stop this?

Sounds like you need some liquid plumber, or the roto-rooter guy.

If the drain can take the water as it is pumped out of the dishwasher, there must be something restricting the flow at some point.

I'd try a couple of treatments with Professional Strength Liquid Plumber first, and if that doesn't do the trick, give the plumber a call and let them snake it out for you.

Does the sink drain normally when using it without the dishwasher? Do you have a garbage disposal ? Post back and let me know and we will try to help. GOOD LUCK, AC

The dishwasher is a pump drain so it will drain the washer even if your sink drain line is plugged, which it is. It might be in the garbage disposer or the traps but I'd put money one the lateral line going into the wall after the trap. Disassemble the trap and rod into the lateral, you'll hit a 90 elbow just 2" inside so start with a small 1/4" rod.

Let me add a bit to Bobs post. First off As a repair plumber I have never recommended using harsh chemicals.in your drainage system. Besides they only seem to work in TV commercials and when you try to remove the water you could burn your hands or damage your eyes. You need to snake the horizontal drain in the wall. Remove the "J" bend from the trap and send a snake up inti the wall. (see image). The picture's a lavatory but the idea's the same. Good luck, Tom

Tom and I agree about Liquid plumber and the harsh chemicals being unnecessary but we have our own liquid concoctions that help and won't burn you, they just aren't appropriate for this situation, a 1/4" rod is appropriate.