LG Refrigerator Error Code 21

Error code 21 on an LG refrigerator indicates a fan motor system abnormality in the CF (compartment freezer) section. This code is triggered when the refrigerator's control board detects a problem with the feedback signal line of the CF compartment fan motor. The feedback signal line is how the motor communicates its actual rotational speed back to the main control board. When this signal is absent, intermittent, or outside the expected parameters, the board logs error 21 and typically shuts down or limits operation of that fan circuit.

There are three primary failure points the code is designed to flag. First, a contact failure on the feedback signal line, meaning a loose connector, corroded pin, or broken wire in the harness that carries the tachometer or Hall sensor signal back to the control board. Second, a missing or broken motor wire, which can occur from physical damage, vibration fatigue, or a manufacturing defect in the wiring harness. Third, an actual defect within the fan motor itself, such as a failed Hall effect sensor inside the motor body, a seized rotor bearing, or damaged motor windings that prevent the motor from spinning and generating a valid feedback signal.

Diagnosis should begin by physically inspecting the CF compartment fan motor wiring harness for any disconnected, corroded, or broken connectors. Verify that the motor wire is fully seated at both the motor and control board ends. If the wiring checks out, observe the fan motor during operation to confirm it is actually spinning. A motor that is not rotating, or rotating erratically, with intact wiring points to a failed motor assembly requiring replacement.