LG Air Conditioner Error Code 42

Error code 42 on an LG air conditioner indicates a fault with the outdoor unit's low pressure sensor. The control board has detected either an open circuit or a short circuit in the sensor signal line. This causes the system to shut down to prevent compressor damage. The issue may be as simple as a loose connector or as involved as a failed sensor or damaged wiring.

No. Error code 42 will typically prevent the unit from operating as a built-in protection measure, and you should not attempt to override this shutdown. The low pressure sensor protects the compressor from running under abnormal refrigerant conditions that could cause permanent damage. Operating the system without a functioning low pressure sensor removes that protection entirely.

Repair costs depend on what component has failed. If the fix is simply reseating a loose connector, the cost is limited to a service call fee, typically in the range of $75 to $150. Replacing the low pressure sensor generally costs between $100 and $300 including parts and labor. If the outdoor PCB requires replacement, costs can rise to the $300 to $600 range or higher depending on the unit model.

A homeowner can safely check that the sensor connector is properly plugged into the PCB in the outdoor unit and inspect the visible wiring for obvious damage. However, further diagnosis requires understanding electrical circuits and working around refrigerant components, which is best left to a qualified technician. Replacing the low pressure sensor or PCB also requires accessing refrigerant lines in some configurations, which may require EPA certification.

A power reset may temporarily clear the error code, but it will return if the underlying sensor fault is still present. Because error code 42 indicates a hardware condition such as an open or short circuit, the fault will persist until the wiring, connector, or sensor is repaired or replaced. Relying on resets without addressing the root cause risks eventual compressor damage.