LG Heat Pump Error Code G4

The G4 code on an LG heat pump indicates that the oil temperature sensor on the compressor sump has likely separated or lost contact with the compressor. The system monitors for at least a 2°C temperature change during the first 30 minutes after startup, and if that change is not detected, it flags a G4 fault. This is a protective diagnostic to ensure the compressor's oil temperature is being accurately monitored.

Running the unit while G4 is active is not recommended. The oil temperature sensor protects the compressor by monitoring lubrication conditions, and operating without accurate sensor data removes a key safeguard against compressor damage. Continued operation could risk expensive compressor failure if an actual lubrication issue goes undetected.

If the repair only involves reseating the sensor, labor costs may be modest, typically in the range of $75 to $150 depending on your technician's rates. If the sensor itself needs replacement, parts and labor combined can range from $150 to $400 or more. A full compressor-related repair would cost significantly more, which is why addressing G4 promptly is important.

Start by locating the oil temperature sensor on the compressor sump and checking whether it has come loose or detached. If it has separated, reseat it firmly against the compressor body and secure it properly. If the sensor is physically intact and properly mounted but the error persists, the sensor itself or its wiring harness may need to be tested or replaced.

Resetting the unit may temporarily clear the fault code, but G4 will return if the underlying sensor issue is not resolved. Because the fault is triggered by a thermal response check during startup, the system will re-detect the problem within the first 30 minutes of the next compressor run cycle if the sensor is still not properly seated.