Bosch dishwashers are built with flood switches located in the bottom base pan of the dishwasher. The flood switch is connected to a rod that activates a small interlock switch, when water enters the base pan on a Bosch dishwasher a Styrofoam puck lifts the rod activating the flood switch.
When the flood switch is activated the dishwasher will go into a no fill, only drain mode, the drain motor may also run with the door open to the unit, this is a sign there is water in the base pan.
Determining where the water entered the base pan can often times be time consuming. Bosch dishwashers have a more complex wash and dry system, more parts this mean smaller work areas, some parts are in sealed compartments, these require lots of time and effort to access.
You may have to watch the unit through a complete cycle before you can diagnose the error. Some of the more common possibilities include
-Sump fill hose (Cracked/brittle)
-Drain hose(Also check drain hose connection)
-Faulty drain pump seal
-Circ pump housing’
-Main sump seal
Any one of these are a possibility and there are many more, spending an hour watching the unit cycle may be the only way to figure out where the water is coming from.
Note also over sud-sing will also cause the unit to leak water into the drain pan. If you recently filled the dishwashers jet dry dispenser, excess jet dry on the door and surrounding areas could create the dishwasher to flood into the pan.