Safety First: Unplug the microwave. Do not touch high-voltage components when the cover is removed.

Steps:

Locate humidity sensor: On many Frigidaire over-the-range models, the humidity sensor is located behind a small grille or opening inside the cavity, often on the upper left or right side.
Clean sensor area: Gently clean the sensor opening and surrounding area with a soft cloth and mild detergent. Remove any grease or food residue.
Access sensor (if needed): Remove the outer cabinet to access the sensor from the side. Follow the small sensor harness to the control board.
Check wiring: Inspect the harness for damage and ensure connectors are fully seated at both ends.
Replace sensor: If F4 persists, replace the Frigidaire humidity sensor with the correct part for your model.
Control board check: If a new sensor does not clear F4, the main control board may be defective and should be tested/replaced by a technician.

Microwave displays F4 and will not operate.

Possible Causes