Frigidaire · Microwave Moderate

F4 — Humidity sensor fault

F4 indicates the humidity (steam) sensor used for Sensor Cook cycles is open, shorted, or out of calibration. Manual time-cook cycles may still work; sensor cooking will fail.

Keep using it?
Yes, with caution
DIY difficulty
Moderate
Verified against
frigidaire.com ↗

How to fix it

  1. Unplug for 5 minutes to clear the fault.
  2. Locate the humidity sensor (usually in the exhaust duct) per the tech sheet.
  3. Inspect for grease buildup; clean the sensor face gently with isopropyl alcohol.
  4. Reseat the harness connector at sensor and board.
  5. Run a Sensor Cook cycle — if F4 returns, replace the humidity sensor.
  6. If a new sensor still throws F4, replace the control board.

Why it happens

Typical signs: F4 displayed when starting Sensor Cook / Auto Reheat · Popcorn / Reheat ends almost immediately or never ends · Manual cook still works

  • Failed humidity / steam sensor Grease film or age has killed the sensor element.
  • Disconnected sensor harness Connector worked loose at the sensor or control board.
  • Blocked exhaust path Steam cannot reach the sensor, so it never sees humidity.

Parts you may need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

  • Frigidaire microwave humidity sensor Common replacement
    Amazon →

More Frigidaire microwave codes

Child Lock 'Lock' / 'L' — Child lock engaged Cooling Fan 'Cooling Fan' / Fan-runs-after-cooking — Vent fan stuck on Demo 'Demo' / 'd' — Showroom demo mode on door 'door' message — Door not fully closed F1 F1 — Control board / thermistor open F2 F2 — Keypad / Control Board Input Fault

All Frigidaire codes → All microwave codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: frigidaire.com.