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Error code reference

LG Refrigerator Error Code F-DEF-SENSOR

F compartment defrosting sensor error

LG codesLG refrigerator codes

F compartment defrosting sensor error: electric wire cut, short-circuit, contact failure, or sensor housing missing; displayed when sensor temperature is not lower than 122°F nor higher than -58°F.

First step from the service manual

Check the voltage between Main PCB CN 30 No. 4 ↔ 7 to see if it is between 4.5V and 1.0V.

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

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What F-DEF-SENSOR means on a LG refrigerator

The F-DEF-SENSOR error on an LG refrigerator indicates a fault with the defrost sensor located in the F compartment (freezer). This sensor monitors temperatures during the defrost cycle to prevent the heater from running too long or too short. The control board triggers this code when the sensor reports a temperature outside the valid range, specifically when the reading is not lower than 122°F and not higher than -58°F. In practical terms, the board is seeing a signal that falls outside what a functioning sensor would ever report under normal operating conditions.

The error is caused by one of four conditions: an open circuit in the sensor wiring (broken wire), a short circuit, a loose or corroded connector causing contact failure, or the sensor housing being missing or improperly seated. Each of these conditions corrupts the resistance-based signal the sensor sends to the Main PCB. The first diagnostic step is to measure the voltage between pins 4 and 7 on connector CN 30 of the Main PCB. A reading between 1.0V and 4.5V indicates the wiring and board side are intact, pointing suspicion toward the sensor itself. A reading outside that range suggests a wiring fault or board issue.

Because the defrost sensor directly governs when the defrost heater shuts off, a failed sensor can lead to two secondary problems: frost accumulation from an incomplete defrost cycle, or potential overheating of the evaporator coils if the heater runs unchecked. Addressing this error promptly is important to protect both the evaporator assembly and the food stored in the compartment.

Source: manufacturer service documentation.

Common causes of F-DEF-SENSOR

  1. 01

    Open circuit or broken sensor wire

    Part replacement

    A broken wire in the sensor harness cuts the signal entirely, causing the board to read an out-of-range value. Check the wiring from the sensor back to CN 30 on the Main PCB for any visible breaks or damage.

  2. 02

    Loose or corroded connector at CN 30

    Wiring / connection

    Contact failure at the connector between the sensor harness and the Main PCB is a common cause. Inspect pins 4 and 7 of CN 30 for corrosion, bent pins, or a loose fit and reseat the connector firmly.

  3. 03

    Failed defrost sensor

    Part replacement

    The sensor itself can fail internally due to age or moisture exposure, causing it to report resistance values outside the acceptable range. If the wiring checks out and the voltage at CN 30 is abnormal, the sensor should be replaced.

  4. 04

    Short circuit in sensor wiring

    Part replacement

    A short in the harness can pull the voltage reading at CN 30 outside the 1.0V to 4.5V window. Look for pinched or chafed wiring, especially near any ice-prone areas in the freezer compartment.

  5. 05

    Missing or improperly seated sensor housing

    Wiring / connection

    If the sensor is not properly clipped into its housing bracket, it may not make reliable contact or may read ambient air rather than the evaporator temperature. Verify the sensor is fully seated in its correct mounting location.

See the test procedure for each cause

Frequently asked questions about F-DEF-SENSOR

What does F-DEF-SENSOR mean on a LG refrigerator?
The F-DEF-SENSOR code means the refrigerator has detected a fault with the defrost sensor in the freezer compartment. The sensor is reading a temperature outside the valid range, specifically not below 122°F and not above -58°F, which signals to the control board that something is wrong. The cause is typically a broken wire, short circuit, connector failure, or missing sensor housing. The first step in diagnosing it is checking the voltage at pins 4 and 7 of connector CN 30 on the Main PCB.
Can I fix the F-DEF-SENSOR error myself?
Some causes of this error are DIY-friendly, such as reseating a loose connector at CN 30 on the Main PCB or checking for obvious wiring damage. If the sensor itself has failed, replacing it requires accessing the freezer evaporator area, which involves removing shelves, panels, and sometimes ice buildup. Technicians with basic electrical testing skills and a multimeter can usually trace this fault with the voltage check at CN 30 as the starting point.
Is it safe to keep using my refrigerator while this error is showing?
Continued use with an active F-DEF-SENSOR error carries some risk. Without a working defrost sensor, the freezer may accumulate excessive frost or, depending on the failure mode, the defrost heater may not shut off at the correct time. Either condition can eventually lead to cooling problems or damage to the evaporator. It is best to address the error promptly rather than leaving the unit running indefinitely in a faulted state.
How much does it cost to repair the F-DEF-SENSOR error on an LG refrigerator?
If only the defrost sensor needs to be replaced, parts typically cost between $15 and $50 depending on the specific model. Labor from an appliance technician generally adds $80 to $150 or more depending on your location and the complexity of accessing the evaporator. If the Main PCB is found to be the cause, board replacement costs significantly more, often ranging from $150 to $350 for parts alone.
Will resetting the refrigerator clear the F-DEF-SENSOR error?
A power reset may temporarily clear the error code from the display, but it will return if the underlying fault is still present. The sensor or wiring issue must be physically diagnosed and corrected before the code will stay cleared. Using a reset as a diagnostic step can be useful to confirm whether the fault is intermittent, but it is not a repair.

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