Microwave displays F4 and will not start or stops mid-cycle.

Safety: Unplug the microwave before removing any covers or panels.

• Clean the interior: Wipe down the oven cavity, especially near the humidity sensor opening (often on the upper side wall or ceiling). Remove grease and food residue that may coat the sensor.
• Allow to dry: If the error appeared after heavy steaming, leave the door open and let the unit dry for several hours.
• Access the humidity sensor: Remove the outer cover or interior trim to locate the small sensor module connected by a wire harness near the cavity wall.
• Inspect connections: Check the sensor plug and wiring for looseness, corrosion, or damage. Reseat the connector firmly.
• Replace sensor: If cleaning and reseating do not clear F4, replace the humidity/steam sensor with a Kenmore-compatible part.

Because the humidity sensor ties into control logic, if a new sensor does not resolve the issue, the main control board may also need replacement by a professional.