Safety first: Unplug the Café microwave or switch off the breaker.

Steps to try:

Clean the cavity: Wipe the interior walls and ceiling with a mild detergent solution, then dry thoroughly. Pay attention to any small grill or opening where the humidity sensor is located (often on the upper side wall).
Ventilate: Leave the door open for 30 minutes to allow moisture to evaporate from the sensor area.
Power reset: Restore power and test a non-sensor cycle (e.g., TIME COOK). If F4 only appears on sensor modes, the humidity sensor is suspect.
Connector check: If you can safely remove the top grille and control panel, locate the humidity sensor (small module with 2–3 wires near the cavity) and ensure its connector is firmly seated.
Persistent F4: The humidity sensor module likely needs replacement. This involves removing the outer cover and working near high-voltage components; have a Café service technician perform this repair.

Microwave shows F4 and will not run; may appear intermittently when using sensor cooking modes.

Possible Causes