LG Microwave Humidity Sensor Replacement — When Auto-Cook Gets It Wrong
LG microwaves with Sensor Cook and Sensor Reheat features use a humidity sensor inside the cooking cavity to detect steam levels. As food heats, it releases moisture. The sensor measures the humidity increase and tells the control board when food has reached the appropriate temperature. When this sensor drifts or fails, auto-cook cycles either overcook (sensor reads low humidity) or undercook (sensor reads high humidity prematurely).
How the Humidity Sensor Works
The sensor is a small thermistor or resistive element mounted in the ceiling or wall of the cooking cavity, usually behind a small cover plate. It detects changes in humidity by measuring the temperature differential between the cavity air and the steam rising from food. As humidity increases, the sensor resistance changes, and the control board adjusts cooking time accordingly.
The sensor needs to start from a cool, dry baseline to work correctly. This is why LG recommends waiting at least 1 minute between sensor cook cycles — the cavity needs to cool and the sensor needs to reset.
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Symptoms of Sensor Failure
- Sensor Cook cycles consistently overcook food — the sensor reads low humidity and extends cook time
- Sensor Reheat cycles end too early, food is cold in the center — the sensor reads high humidity prematurely
- The microwave displays a sensor error code — the sensor resistance is out of expected range
- Auto-cook works on some foods but not others — intermittent sensor readings
- Sensor Cook cycle runs the maximum time every time — sensor is not detecting any humidity change
Ruling Out Other Causes
Before replacing the sensor:
- Clean the sensor cover — grease and food splatter on the cover insulate the sensor from steam. Clean the interior of the cooking cavity thoroughly, paying attention to the ceiling area.
- Wait between cycles — running Sensor Cook immediately after a previous cycle means the cavity is already humid. Wait 2-3 minutes.
- Check the vent — if the exhaust fan is running during sensor cooking (on over-the-range models), it pulls steam away from the sensor, confusing the reading. Turn off the vent during sensor cook cycles.
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Appliances involve high voltage (120-240V), pressurized water, gas lines, and chemical refrigerants. Over 400 DIY repair injuries are reported yearly. Our techs are licensed and insured — let them handle the risk.
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Part Numbers and Pricing
| Part | LG Number | Price |
|---|---|---|
| Humidity sensor | 6501KW2002A | $15-$45 |
| Aftermarket sensor | Various | $8-$25 |
| Professional replacement | — | $80-$150 |
Tools Required
- Phillips #2 — for the sensor cover plate inside the cavity and possibly the outer cabinet
- Multimeter (optional) — to test sensor resistance
On many LG models, the sensor is accessible from inside the cooking cavity without opening the cabinet. If the sensor mounts externally (behind the cavity wall), cabinet removal and capacitor discharge are required.
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Replacement Procedure
Unplug the microwave. Locate the sensor inside the cooking cavity — typically behind a small rectangular cover plate on the ceiling or upper wall. Remove the cover plate screws (1-2 Phillips). The sensor is a small component with a wire connector. Disconnect the connector, remove the sensor, install the new one, and replace the cover plate.
If the sensor is mounted externally, you must remove the cabinet and discharge the capacitor to access it. This requires professional expertise due to the high-voltage hazard.
Test by running a Sensor Reheat cycle with a plate of refrigerated food. The microwave should run for 2-4 minutes and the food should come out evenly heated.
Sensor Calibration
After replacing the sensor, run 2-3 sensor cook cycles to allow the control board to calibrate to the new sensor's baseline. The first cycle may overcook or undercook slightly — this is normal as the board learns the new sensor's characteristics.
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Frequently Asked Questions
My LG microwave Sensor Cook always overcooks food. Is the sensor bad?
Clean the cooking cavity first, especially the ceiling area near the sensor. Grease buildup insulates the sensor from steam. If cleaning does not help and you are waiting between cycles, the sensor may need replacement ($15-$45).
Can I use my LG microwave without the sensor?
Yes — manual time and power level settings do not use the sensor. Only Sensor Cook and Sensor Reheat rely on humidity detection. You can cook everything manually.
Does the LG microwave sensor affect defrost mode?
No. Defrost mode uses time and power level calculations based on the weight you enter, not humidity sensing. A failed sensor does not affect defrost performance.
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