LG Refrigerator Error Code R0 ON, R1-R4 OFF

The R0 ON, R1-R4 OFF error code on an LG refrigerator indicates a defrost sensor failure. Specifically, the control board has detected that the defrost sensor circuit is either shorted or open. The defrost sensor is a thermistor that monitors temperature during the defrost cycle, signaling to the control board when the evaporator coils have reached the appropriate temperature to terminate the defrost heater. When this sensor fails or its wiring is compromised, the board cannot accurately manage the defrost cycle, which can lead to ice buildup on the evaporator coils and eventual cooling loss throughout the refrigerator.

An open circuit condition means the electrical path through the sensor or its wiring harness has been broken, resulting in no signal reaching the control board. A short circuit means two conductors that should be electrically isolated are making unintended contact, causing abnormal resistance readings. Both conditions will trigger this fault code. The first diagnostic step is to measure the defrost sensor's resistance with a multimeter and compare it against the expected value for the ambient temperature at the sensor's location. A reading of infinite resistance indicates an open circuit, while a reading near zero ohms indicates a short.

Wiring harness damage is a common contributor to this fault, particularly in areas where the harness is routed near the evaporator coil housing or is exposed to repeated freeze and thaw cycles. Corrosion at the connector terminals, pinched wires, or a failed thermistor element can all produce this error. Because a non-functional defrost sensor disables proper defrost cycle control, addressing this fault promptly is important to prevent compounding cooling problems caused by ice accumulation on the evaporator.