LG Refrigerator Error Code E 4

E 4 on an LG RSG5B* series refrigerator indicates that the main control board has detected an open or short circuit in the freezer defrost sensor. The defrost sensor monitors freezer temperature during defrost cycles and sends a variable voltage signal back to the PCB. When that signal falls outside the expected 1.0V to 4.5V range at connector CN30 pins 4 and 9, the board triggers the E 4 fault. The refrigerator may continue cooling but defrost operation can be compromised.

The refrigerator may continue to maintain some cooling, but the defrost cycle is likely impaired or non-functional while E 4 is active. Over time, this can cause frost to accumulate on the evaporator coils, which will progressively reduce cooling efficiency and may eventually block airflow entirely. It is best to address the fault promptly to avoid food spoilage or further component damage.

Repair costs vary depending on the failed component. A replacement defrost sensor typically costs between 15 and 50 dollars for the part, with professional labor adding 80 to 150 dollars depending on your area. If the main PCB is the cause, parts alone can range from 100 to 300 dollars or more. Getting a voltage reading at CN30 first helps narrow down the fault and avoids unnecessary part replacements.

A knowledgeable DIYer can handle some steps, such as inspecting the wiring harness, cleaning the CN30 connector, and performing a manual defrost to eliminate ice-related damage as a cause. Voltage testing at CN30 requires a multimeter and basic familiarity with reading electrical circuits. Replacing the defrost sensor is a straightforward part swap for most technicians, but if the main PCB is at fault, professional diagnosis is recommended before purchasing a replacement board.

A power reset by unplugging the unit for a few minutes may temporarily clear the error code display, but it will return if the underlying sensor fault has not been resolved. The main PCB continuously monitors the voltage signal from the defrost sensor, so any open or short circuit condition will trigger E 4 again once the board runs its diagnostic routine. A reset alone is not a fix.