LG Refrigerator Error Code R2 R4 ON

The R2 R4 ON error code on an LG refrigerator indicates an open or short circuit condition in one or both of the defrost sensors. These sensors are thermistors positioned within the evaporator section of the refrigerator and freezer compartments. Their job is to monitor evaporator coil temperature during and after the defrost cycle, signaling the control board when the coil has reached the target temperature so the heater shuts off. When the control board detects that a sensor's resistance reading falls outside the expected range, either infinitely high due to an open circuit or near zero due to a short, it triggers this error.

An open circuit condition typically means the thermistor element has failed internally or the wiring harness has a break somewhere along the circuit. A short circuit means the sensor leads or wiring have made unintended contact with each other or with a ground point. Both conditions prevent the control board from receiving accurate temperature data, which can cause the defrost cycle to run too long, not run at all, or halt mid-cycle. This leads to frost accumulation on the evaporator coils and eventually reduced cooling performance throughout the refrigerator.

Diagnosing this code requires checking each defrost sensor individually. A technician should disconnect each sensor from the wiring harness and measure its resistance with a multimeter. A properly functioning thermistor will show a resistance value within the expected range for the current ambient temperature. Infinite resistance confirms an open circuit and a faulty sensor. Near-zero resistance confirms a short. Wiring between the sensor and the control board should also be inspected for pinching, corrosion, or damage before replacing any components.