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Error code reference

LG Microwave Error Code C-20

Temperature sensor open or short information code

LG codesLG microwave codes

Temperature sensor open or short information code: temperature sensor value is below 5 or more than 250, oven converts to cancel mode.

First step from the service manual

Check sensor part and connection of sensor housing and PCB's connector.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What C-20 means on a LG microwave

The C-20 error code on an LG microwave indicates a fault condition with the cavity temperature sensor. Specifically, the control system has detected that the temperature sensor is reading a value either below 5 or above 250, which places the reading outside the acceptable operating range. Because this value falls outside the valid threshold window, the microwave interprets the sensor as either open-circuited or short-circuited, and the oven automatically converts to cancel mode to prevent unsafe operation.

The temperature sensor in an LG microwave is a thermistor-based component responsible for monitoring the internal cavity temperature during cooking cycles. When functioning correctly, it produces a resistance value that the PCB translates into a temperature reading within the defined operating range. An open circuit condition, where the sensor or its wiring has failed to maintain continuity, causes the reading to fall below 5. A short circuit condition, where the sensor or wiring has lost insulation integrity, drives the reading above 250. Either scenario triggers the C-20 fault.

The first diagnostic step is to inspect the sensor itself along with the wiring harness connection between the sensor housing and the PCB connector. Loose, corroded, or damaged connector pins are a common culprit, as are physical breaks or shorts in the sensor wiring. If the connector and wiring check out visually and electrically, the sensor component itself should be tested for correct resistance values and replaced if it falls outside specification.

Source: manufacturer service documentation.

Common causes of C-20

  1. 01

    Loose or disconnected sensor connector

    Wiring / connection

    The wiring harness connector between the temperature sensor housing and the PCB can work loose over time due to vibration. A disconnected connector will cause an open-circuit reading, triggering C-20.

  2. 02

    Failed temperature sensor

    Part replacement

    The thermistor inside the sensor component can fail in an open or shorted state, producing a reading outside the valid range of 5 to 250. The sensor must be tested for proper resistance and replaced if defective.

  3. 03

    Damaged sensor wiring harness

    Part replacement

    The wiring between the sensor and the PCB can develop breaks, fraying, or insulation damage, causing either an open or short circuit condition. Inspect the full length of the harness for visible damage.

  4. 04

    Corroded or damaged connector pins

    Wiring / connection

    Moisture or heat exposure can corrode the connector pins at either the sensor housing or the PCB, increasing resistance or breaking continuity. Check both connector ends for corrosion, bent pins, or burnt contacts.

  5. 05

    Faulty PCB

    Part replacement

    If the sensor, wiring, and all connectors test correctly, the PCB may have a defect in the circuit that reads the sensor signal. PCB failure is the least common cause but should be considered after all other components are ruled out.

See the test procedure for each cause

Frequently asked questions about C-20

What does C-20 mean on a LG microwave?
C-20 is a temperature sensor fault code indicating that the sensor reading has fallen outside the acceptable range, specifically below 5 or above 250. This signals an open or short circuit condition in the temperature sensor circuit. When this code appears, the microwave cancels its current operation and will not run until the fault is resolved.
Can I fix the C-20 error myself?
Some causes of C-20, such as a loose connector between the sensor housing and the PCB, can be addressed by a confident DIYer who is comfortable safely disassembling the microwave. However, microwave capacitors store lethal voltage even when unplugged, so the repair requires discharging the capacitor before touching any internal components. If you are not experienced with microwave disassembly and capacitor discharge procedures, professional service is strongly recommended.
Is it safe to use my LG microwave while the C-20 code is showing?
No, you should not attempt to operate the microwave while C-20 is active. The code causes the oven to enter cancel mode specifically to prevent operation without a functioning temperature sensor. Running the microwave without a working temperature sensor could result in overheating or uncontrolled cooking conditions.
Will resetting my LG microwave clear the C-20 error?
Unplugging the microwave for a few minutes may temporarily clear the error code, but C-20 will return as soon as the microwave attempts to use the temperature sensor again if the underlying fault has not been repaired. A reset does not fix a failed sensor, damaged wiring, or a loose connector. Persistent or recurring C-20 codes require physical inspection and repair.
How much does it cost to repair a C-20 error on an LG microwave?
Repair costs vary depending on the cause. If only a connector needs reseating, there may be no parts cost and a modest diagnostic labor fee, typically in the range of $50 to $100. Replacing the temperature sensor itself generally costs between $75 and $175 including parts and labor. PCB replacement, if required, is the most expensive scenario and could range from $150 to $300 or more, at which point evaluating the cost of a new unit may be worthwhile.

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