LG Refrigerator Error Code Sd E

The Sd E error code on an LG refrigerator indicates a communication failure between the Micom (microcomputer controller) on the Display PCB and the Micom on the Ice Maker Sub PCB. These two boards exchange data continuously to coordinate ice making functions, and the Sd E code triggers when that communication link breaks down or becomes unreliable. The error points specifically to the serial communication pathway between the two controllers rather than a fault in the ice making mechanism itself.

The most likely root causes involve the physical communication circuit connecting the two boards. Poor or intermittent connections at the wiring harness are frequently responsible, as vibration and thermal cycling over time can cause connectors to loosen or corrode. The error can also originate from a failure in the transmitter and receiver transistors (Tx/Rx) on either board, which are the components responsible for sending and receiving the serial data signals between the Display PCB and the Sub PCB.

Diagnosis begins with inspecting connector CON102 on the relevant board and measuring voltage at pins 3 through 5 and pins 3 through 9. A healthy communication line will show a voltage that fluctuates between these thresholds rather than holding steady at 0V or 5V. A reading stuck at 0V suggests an open circuit or a failed transmitter, while a reading locked at 5V can indicate a short or a receiver transistor fault. Based on these readings, the technician can determine whether the issue is a harness problem or a PCB component failure.