Initial thought is probably a bad impeller on the circulation pump. Might check first for obstructions to the intake side of the circulation pump. If something has gotten down into that it would cause the same symptom. If that looks clear you'll have to pull the dishwasher out to check the impeller. The Bosch models I'm familiar with have a 5/16" "nut" shape on the center of the impeller accessible from inside the dishwasher at the circulation intake port. You can put a 5/16" socket on an extension to engage with your left hand or a helper and gently rotate it clockwise while watching to see if that turns the fan blades of the circulation motor at the right underside of the dishwaser (need to remove side cover to see this). The impeller is mounted directly to the motor shaft so both should turn as a single unit - any slippage indicates an impeller failure. The impeller threads onto the shaft with normal right hand threads but should only be on hand tight so when turning don't over tighten or turn in the opposite direction so as to loosen it from the shaft. If you do happen to loosen it just tighten it back up by tightening while restricting motor blade movement.