Microwave stops and displays E04, often when using sensor cooking or auto programs.

Safety: Unplug the microwave before cleaning inside surfaces.

• Clean the cavity thoroughly: Food splatter and grease on the ceiling and side walls can interfere with the Bosch humidity sensor. Wipe the interior with a soft cloth and mild detergent. Avoid spraying cleaner directly into vents or sensor openings.
• Locate and clean sensor area: On many Bosch models, the humidity sensor is behind a small grill or opening on the upper side wall or ceiling. Gently clean around this area with a damp cloth; do not insert objects into the opening.
• Dry completely: Leave the door open for 30 minutes to allow moisture to evaporate.
• Reset power: Plug the unit back in and test a manual time-cook function first. Then test a sensor program with a small load (e.g., reheating a plate of food).

If E04 persists: The humidity sensor or its wiring may be defective, or the control board sensor circuit may have failed. These parts are behind the control panel and require disassembly; contact Bosch service.