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Error code reference

LG Refrigerator Error Code F-defrost sensor open

Freezer area defroster sensor open circuit fault

LG codesLG refrigerator codes

Freezer area defroster sensor open circuit fault - sensor reading suspected to be below -50°C.

First step from the service manual

Check F-defrost sensor resistance and wiring; replace sensor if faulty.

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

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  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
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What F-defrost sensor open means on a LG refrigerator

The F-defrost sensor open error on an LG refrigerator indicates an open circuit fault in the freezer area defrost sensor. This sensor monitors temperature during the defrost cycle to prevent overheating and to confirm that frost has been properly cleared from the evaporator coils. When the refrigerator's control board reads a signal consistent with a temperature below -50°C, it interprets this as an open circuit rather than a valid temperature reading, and triggers the fault code. An open circuit means the electrical signal path through the sensor has been broken entirely.

The defrost sensor is a negative temperature coefficient (NTC) thermistor, meaning its resistance decreases as temperature rises. A properly functioning sensor operates within a predictable resistance range that corresponds to actual freezer temperatures. When the sensor or its wiring develops an open circuit, the control board receives an out-of-range resistance reading, which it maps to a temperature below -50°C. This is a signal integrity failure, not necessarily a true temperature condition inside the freezer compartment.

Common causes include a failed thermistor element inside the sensor, damaged wiring harness connections between the sensor and the control board, or corrosion at the connector pins. Physical damage from ice buildup around the sensor body can also stress and break the internal element or connected wires. Diagnosing this fault requires measuring the sensor's resistance with a multimeter and inspecting the wiring for breaks, corrosion, or loose terminals before concluding the sensor itself needs replacement.

Source: manufacturer service documentation.

Common causes of F-defrost sensor open

  1. 01

    Failed defrost sensor thermistor

    Part replacement

    The thermistor element inside the sensor can fail and create an open circuit, producing a resistance reading that falls outside the valid range. Measuring the sensor's resistance with a multimeter and comparing it to the expected range for the ambient temperature will confirm this failure.

  2. 02

    Broken or damaged wiring harness

    Part replacement

    The wires connecting the defrost sensor to the control board can develop breaks due to ice pressure, repeated freezing and thawing cycles, or physical stress during installation. Visually inspect the harness for cuts, kinks, or frayed insulation and use a multimeter to check continuity along the wire run.

  3. 03

    Corroded or loose connector pins

    Wiring / connection

    The connector terminals between the sensor wiring and the control board can corrode or back out of the connector housing, interrupting the circuit. Disconnecting and closely inspecting the connector for oxidation, bent pins, or loose terminals can identify this issue.

  4. 04

    Ice buildup around the sensor body

    Wiring / connection

    Excessive ice accumulation around the sensor can physically stress the sensor body and its wire connections, causing an internal break. Defrosting the unit manually and then re-testing the sensor resistance will help determine if ice damage has caused a permanent failure.

  5. 05

    Control board communication fault

    Part replacement

    In less common cases, the control board itself may misread an otherwise functional sensor circuit. This should only be considered after the sensor resistance and wiring have been confirmed as good through direct measurement.

See the test procedure for each cause

Frequently asked questions about F-defrost sensor open

What does F-defrost sensor open mean on a LG refrigerator?
This error means the control board has detected an open circuit in the freezer area defrost sensor. The sensor's resistance reading has fallen outside the valid range, which the board interprets as a temperature below -50°C. This typically points to a failed sensor thermistor, a broken wire, or a poor connection in the sensor circuit. The freezer's ability to properly manage defrost cycles may be compromised until the fault is resolved.
Can I fix the F-defrost sensor open error myself?
A knowledgeable DIYer can often diagnose this fault by testing the defrost sensor's resistance with a multimeter and inspecting the wiring harness and connectors for damage or corrosion. If the sensor itself has failed, replacing it is a straightforward repair that involves unplugging the refrigerator, accessing the sensor in the freezer compartment, and swapping in the correct replacement part. If the wiring or control board is involved, the repair becomes more complex and may benefit from professional service.
Is it safe to keep using my LG refrigerator when the F-defrost sensor open error is showing?
The refrigerator may continue to cool in the short term, but without a functioning defrost sensor, the defrost cycle cannot operate correctly. Over time this can lead to excessive frost buildup on the evaporator coils, reduced cooling efficiency, and potential damage to other components. It is best to address the fault promptly rather than continue running the unit with the error active.
How much does it cost to repair the F-defrost sensor open error on an LG refrigerator?
If only the defrost sensor needs replacement, parts typically cost between $15 and $50 depending on the specific model, and a DIY repair involves minimal additional expense. A professional repair, including parts and labor, generally ranges from $100 to $250. If the wiring harness or control board is also involved, costs can be higher.
Will resetting my LG refrigerator clear the F-defrost sensor open error?
A reset may temporarily clear the error code from the display, but the fault will return as long as the underlying problem with the sensor or wiring exists. The control board will detect the open circuit again during its next diagnostic cycle. Resetting the unit without completing a proper repair does not fix the sensor and should not be used as a substitute for diagnosing the root cause.

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