LG Freezer Error Code 4

Error code 4 on an LG freezer indicates that the freezer defrost sensor (F-DEF-SENSOR) has been detected as either open or shorted by the main control board. The sensor is a thermistor that monitors temperature during the defrost cycle. The board checks the signal voltage at connector CN30 pins 3 and 8, and if that voltage falls outside the 1.0V to 4.5V operating range, this code is triggered.

Resetting the freezer by unplugging it for a few minutes may temporarily clear the error code, but if the underlying defrost sensor fault is still present, the code will return once the unit restarts and runs its diagnostics. A reset is useful for confirming whether the fault is persistent, but it does not address the root cause.

If only the defrost sensor thermistor needs replacement, repair costs are typically in the range of $50 to $150 including parts and labor. If the issue involves wiring harness repair, the cost may be somewhat higher. Main PCB replacement is the most expensive scenario, generally ranging from $150 to $400 or more depending on the specific unit and service provider.

Technicians and experienced DIYers can diagnose this error by checking the voltage at the main PCB connector CN30 between pins 3 and 8. If the sensor is faulty, replacing the defrost thermistor is a manageable repair involving disconnecting the old sensor and installing a compatible replacement. Wiring harness repairs or main PCB replacement are more involved and may warrant professional service.

Continuing to run the freezer with error code 4 active is not recommended for an extended period. Without a functioning defrost sensor, the defrost cycle may not operate correctly, leading to frost buildup on the evaporator coil. Over time this can restrict airflow and reduce the freezer's ability to maintain safe storage temperatures.