LG Air Conditioner Error Code E251

E251 indicates a condenser temperature sensor error or compressor discharge temperature sensor error. The control board has detected a voltage signal from one of these sensors that is either above 4.9V (corresponding to approximately -50°C) or below 0.4V (corresponding to approximately 93°C). Both thresholds are outside the valid operating range, so the unit shuts down to protect itself. The most common fix is replacing the faulty sensor after powering the system off completely.

No. The condenser and compressor discharge temperature sensors exist specifically to protect the compressor and refrigerant circuit from overheating or operating outside safe parameters. Running the unit while these sensors are reporting invalid data removes an important layer of protection and could lead to compressor damage. The unit should remain off until the fault is diagnosed and the sensor is repaired or replaced.

Repair costs vary depending on which sensor is faulty and local labor rates. A replacement temperature sensor part typically costs in the range of $15 to $60 depending on the specific unit model. With professional labor included, total repair costs generally fall somewhere between $100 and $300. If the fault has caused secondary damage to the control board, costs will be higher.

Checking for disconnected or corroded sensor connectors is a task many experienced DIYers can handle safely after the unit is fully powered off. However, identifying which specific sensor has failed, testing resistance values, and replacing components inside the outdoor unit typically requires familiarity with HVAC electrical systems. If you are not comfortable working around electrical components in an outdoor unit, contacting a licensed HVAC technician is the safer option.

A power reset may temporarily clear the error code from the display, but the fault will return as soon as the control board reads the sensor signal again and detects it is still outside the valid voltage range. A reset does not fix the underlying hardware problem. The sensor, wiring, and connectors must be inspected and any defective component must be replaced before the error will clear permanently.