ge nautilus wont drain common question

Hello,
I have a ge nautilus dishwasher that wont drain. It runs fine otherwise- water pumps strong and all sprayers work during wash. As I slowly turn the dial to find drain times i see the drain switch, arm, lever thing underneath quickly try to drain but it immediately disengages. If i manually push it it drains quickly. but not on its own??? Ive read many similar threads, Ive done some extensive and successful appliance repairs before so a little advice and I should be fine.
Thanks so much!! - Sparky