Here is your parts breakdown
Model HDA1100Z04WH

First thing to check is the solenoid (left side front) on the pump module.
Make sure it is returning to home position, there should be a spring which does this.
Solenoid up is wash, solenoid down is pump out. It runs a flapper valve which redirects the water.
IF OK then I would check the flapper valve itself. Often they have a black rubber seal in the center, this may be missing. Also check this area for debris, anything that might hold the valve partially open. You will have to remove the spray arm assy some just unscrew and have a bolt inside that has to be undone. Other just unscrew (could be reverse thread), also may have a clip at the bottom which has to be released. See below link.

While you are at it you might as well remove the filter cover and check for debris and stuff wound around the chopper. Take note how the plastic piece under the filter goes in and mark it, put it in wrong and the chopper will eat it up.

Next would be the piston nut at the back of the machine, accessible from inside.

http://www.applianceaid.com/dishwash.html