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Error code reference

LG Refrigerator Error Code F-DEF-SEN

Freezer defrost sensor failure detected by self-diagnosis.

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Freezer defrost sensor failure detected by self-diagnosis.

First step from the service manual

Check resistance at CN30 No.4 ↔ No.7; 0Ω indicates short failure, ∞Ω indicates open failure.

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

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What F-DEF-SEN means on a LG refrigerator

The F-DEF-SEN error code on an LG refrigerator indicates that the freezer defrost sensor has failed the unit's self-diagnostic check. The defrost sensor is a thermistor responsible for monitoring freezer temperature during the defrost cycle, signaling the control board when the evaporator has reached the appropriate temperature to terminate defrost. When this sensor fails or its circuit is compromised, the refrigerator cannot safely manage the defrost cycle, which can lead to ice buildup on the evaporator coil and eventual cooling loss throughout the unit.

Diagnosis begins at connector CN30 on the control board, specifically between pins No.4 and No.7, which carry the sensor signal circuit. A resistance reading of 0 ohms at these pins indicates a short circuit failure, meaning the sensor wiring or the sensor itself has an internal short. A resistance reading of infinity (open circuit) indicates a broken wire, disconnected connector, or a failed thermistor element that has lost continuity. Normal thermistor resistance will fall within a finite range that varies with temperature, so any reading at either extreme points to a definitive circuit fault rather than a calibration issue.

The most common root causes include a defective thermistor, damaged wiring harness leads between the sensor and the CN30 connector, or a corroded connector. Physical damage from ice accumulation around the evaporator area can also stress the sensor wiring over time, causing an intermittent or permanent open circuit. In less common cases, the control board itself may have a fault at the CN30 input, though this should only be considered after the sensor and wiring have been ruled out.

Source: manufacturer service documentation.

Common causes of F-DEF-SEN

  1. 01

    Failed defrost sensor thermistor

    Part replacement

    The thermistor element inside the defrost sensor can fail open or short internally. Resistance measured between CN30 pins No.4 and No.7 will read either 0 ohms (short) or infinity (open) instead of a finite value.

  2. 02

    Damaged or broken wiring harness

    Part replacement

    Wires running from the defrost sensor to the CN30 connector can develop breaks or shorts due to ice buildup, freezer door flexing, or physical abrasion over time. Inspect the harness for visible cuts, kinks, or frost damage along its entire length.

  3. 03

    Corroded or loose CN30 connector

    Wiring / connection

    Moisture intrusion into the CN30 connector can cause corrosion at pins No.4 or No.7, increasing resistance to infinity or causing intermittent contact. Disconnect and inspect the connector for oxidation, bent pins, or debris.

  4. 04

    Ice accumulation shorting or stressing the sensor

    Wiring / connection

    Excessive ice formation around the evaporator can physically damage the sensor body or clamp down on the wiring, causing a short or open condition. A full manual defrost should be performed before testing to eliminate ice as a contributing factor.

  5. 05

    Faulty control board at CN30 input

    Part replacement

    If the sensor and wiring both test correctly, the control board may have an internal fault at the CN30 sensor input circuit. This is the least likely cause and should only be diagnosed after all other components are confirmed good.

See the test procedure for each cause

Frequently asked questions about F-DEF-SEN

What does F-DEF-SEN mean on a LG refrigerator?
F-DEF-SEN means the refrigerator's self-diagnostic system has detected a failure in the freezer defrost sensor circuit. The defrost sensor is a thermistor that monitors evaporator temperature during the defrost cycle and signals the control board when defrost should stop. The error is confirmed by checking resistance at connector CN30 between pins No.4 and No.7, where a reading of 0 ohms indicates a short and a reading of infinity indicates an open circuit.
Can I fix the F-DEF-SEN error myself?
A knowledgeable DIYer with a multimeter can diagnose this code by testing resistance at CN30 pins No.4 and No.7 after unplugging the refrigerator. If the wiring harness shows visible damage or the connector is corroded, those repairs are relatively straightforward. Replacing the defrost sensor thermistor is also a common DIY repair, but if the control board is determined to be at fault, professional service is recommended.
Is it safe to keep using my LG refrigerator with the F-DEF-SEN error?
Continued use is not recommended for an extended period. Without a functioning defrost sensor, the refrigerator cannot properly control the defrost cycle, which can lead to ice buildup on the evaporator coil and gradual loss of cooling performance in both the freezer and fresh food compartments. Food safety may be at risk if temperatures rise beyond safe storage levels.
How much does it cost to repair the F-DEF-SEN error on an LG refrigerator?
If only the defrost sensor thermistor needs replacement, parts typically range from around 15 to 50 dollars depending on the specific model. Professional labor to diagnose and replace the sensor generally adds 100 to 200 dollars. If the control board is the cause, parts and labor costs can range from 200 to 500 dollars or more.
Will resetting my LG refrigerator clear the F-DEF-SEN error code?
A power reset may temporarily clear the error code from the display, but the code will return if the underlying sensor or wiring fault is not repaired. Because this error is generated by the refrigerator's self-diagnostic system detecting a measurable circuit fault, the root cause must be corrected before the error will clear permanently.

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