LG Refrigerator Error Code R1 R2 R3 R4 (blinking pattern 2)

The R1 R2 R3 R4 blinking pattern 2 error code on an LG refrigerator indicates a fault with the defrost sensor, also referred to as the D sensor. This sensor monitors the temperature of the evaporator during the defrost cycle, signaling the control board when the evaporator has reached the appropriate temperature to terminate defrost. When the sensor circuit is either open or short-circuited, the control board cannot receive valid temperature data and will suspend defrost operation entirely to prevent component damage. Without periodic defrost cycles, the evaporator coil will accumulate frost over time, eventually blocking airflow and causing cooling performance to degrade significantly.

Diagnosing this fault begins at Point B in the sensor circuit, where voltage readings directly indicate the nature of the failure. Under normal operating conditions, the voltage at Point B should fall within the range of 0.5V to 4.5V, varying with evaporator temperature. A reading of 0V at Point B indicates a short-circuit condition in the sensor or its wiring, while a reading of 5V indicates an open circuit, meaning the signal path is broken entirely. Both conditions render the sensor unable to communicate valid data to the control board. Resistance testing of the sensor itself can further confirm whether the component has failed internally or whether the fault lies in the wiring harness or connector leading to it.

Common causes include physical failure of the defrost sensor element, damage to the wiring harness running to the sensor, and corroded or loose connector pins at the sensor plug. In some cases, moisture intrusion into the sensor housing or connector can cause intermittent short-circuit readings. Because the refrigerator will not perform any defrost while this fault is active, technicians should also assess the evaporator for heavy frost accumulation before restoring power after the repair.