Microwave displays F4 and will not run, often associated with sensor cooking functions.

Safety first: Unplug the microwave before removing the cabinet. Avoid contact with the high-voltage capacitor and magnetron area.

• Power reset: Unplug for 5–10 minutes, then reconnect and test. If F4 reappears immediately, proceed to inspection.
• Access the sensor: Remove the outer cabinet. Locate the sensor on the cavity wall or top, usually a small probe or plastic-encased device with two wires.
• Check connections: Ensure the sensor plug is fully seated on both the sensor and control board ends. Look for corrosion or loose pins.
• Inspect wiring: Follow the harness and look for breaks, burns, or pinched sections where the cabinet may have cut the wire.
• Replace sensor: If wiring is intact but F4 persists, replace the cavity temperature/humidity sensor.
• Control board diagnosis: If a new sensor and good wiring still give F4, the main control board is likely faulty and should be replaced by a professional.