LG Air Conditioner Error Code E257

E257 indicates a fault on the discharge temperature sensor for compressor 2. The control board has detected either a short circuit or an open circuit in the sensor circuit, meaning the temperature reading is outside the valid range. As a safety response, the system limits or stops compressor 2 operation until the fault is corrected.

Running the system with E257 active is not recommended. The discharge temperature sensor for compressor 2 is a protective device, and without valid temperature data the system cannot detect an overheating compressor in time to prevent serious damage. Continued operation under this fault risks compressor failure, which is a costly repair.

Repair costs vary depending on the failed component. A replacement discharge temperature thermistor is generally an inexpensive part, with parts and labor typically ranging from around 80 to 200 dollars for a straightforward sensor swap. If the wiring harness needs replacement the cost is somewhat higher, and PCB replacement is the most expensive scenario, potentially ranging from 300 to 600 dollars or more depending on the unit model and labor rates in your area.

Some causes, such as a loose connector at the PCB, can be addressed by a knowledgeable DIYer who is comfortable working inside the unit with power disconnected. However, measuring sensor resistance accurately, inspecting the wiring harness near a high-pressure compressor line, and diagnosing PCB faults requires tools and experience that typically call for a qualified technician. If you are not confident with electrical diagnostics, professional service is the safer choice.

A power cycle may temporarily clear the displayed code, but if the underlying fault in the sensor, wiring, or connector is still present the error will return once the system restarts and re-checks the sensor circuit. The root cause must be diagnosed and repaired for the code to clear permanently.