LG Microwave F-5 Error: Humidity sensor fault (Auto Cook sensor failure)
LG microwave error — here’s what you need to know. The F-5 error code on your LG microwave indicates a humidity sensor fault — the steam/moisture sensor used by Auto Cook functions has failed or is reading out of range. This is a Low severity issue. What Does F-5 Mean on an LG Microwave? The […]
~55%
DIY Fixable
From $75
Typical Repair Cost
30 min–1.5 hours
Pro Repair Time
Quick Assessment
Answer to continue safely
Is it safe to keep using?
Maybe. Manual timed cooking is generally unaffected by F-5. However, avoid using Auto Cook or sensor programs until the fault is resolved, as the microwave cannot regulate sensor-mode cycles safely.
Can I reset the code?
Yes. A power-cycle reset combined with cleaning the sensor can resolve F-5 when the cause is grease contamination. A persistent F-5 after cleaning indicates a hardware failure that a reset alone cannot fix.
When to stop immediately?
Stop if you notice: F-5 appears even when using timed (non-sensor) cooking modes, The error returns immediately after cleaning and resetting the unit.
Symptoms You May Notice
Auto Cook and sensor programs refuse to start or end prematurely
Sensor-based cooking modes (e.g., Auto Reheat, Sensor Cook) will not initiate or terminate the cycle early because the control board cannot get a valid humidity reading.
F-5 code displayed when selecting an Auto Cook option
The error appears specifically when a sensor cooking mode is chosen, while manual timed cooking may continue to work normally.
Food is consistently undercooked or overcooked in sensor mode
Before a hard fault, a degrading humidity sensor may cause sensor programs to misjudge moisture levels, resulting in poor cooking results before F-5 is formally displayed.
Inconsistent temperature performance
The microwave runs too hot, too cold, or cycles erratically because the control board receives inaccurate temperature readings from the faulty sensor.
Possible Causes
Grease or food film on the humidity sensor
Cooking residue has built up on the sensor's surface (typically on the cavity ceiling), insulating it and preventing accurate moisture readings.
DIY PossibleFailed humidity sensor element
The sensor element has degraded beyond its usable life due to cumulative heat and moisture exposure and is no longer producing a valid output signal.
Requires ProfessionalWiring or control board fault
A loose connector or damaged wire between the sensor and the main PCB, or a control board input circuit failure, produces an F-5 even when the sensor is functioning.
Requires ProfessionalSafe Checks You Can Do
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1
Clean the cavity ceiling and humidity sensor
With the microwave unplugged, wipe the interior ceiling — where the sensor is located — with a damp cloth followed by a dry cloth. Remove any grease film around the small sensor opening. Avoid abrasive cleaners.
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2
Run a plain water test in manual mode
After cleaning, plug in the unit and run a 1-minute timed (non-sensor) cycle with a cup of water to confirm basic heating operation, then try a sensor program again.
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3
Hard reset
Unplug the microwave for 60 seconds to reset the control board, then restore power and retest the sensor cooking modes.
When to Call a Professional
Contact a qualified technician if:
- Error persists after thorough cavity cleaning and multiple power-cycle resets
- Manual timed cooking also fails, suggesting the fault has spread beyond the sensor circuit
- Visible corrosion or damage around the sensor port on the cavity ceiling
Need Professional Help?
Find qualified technicians in your area for proper diagnostics and repair.
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