LG Heat Pump Error Code E407

E407 indicates a fault in the PWM discharge temperature sensor circuit on the outdoor unit. The control board has detected a sensor voltage above 4.95V, indicating an open circuit, or below 0.5V, indicating a short circuit. This error is only triggered when the outdoor temperature is above -10°C. The system stops compressor operation to prevent damage until the fault is resolved.

The system is designed to halt compressor operation when E407 is active, which means running the unit in its degraded state without the discharge temperature being monitored creates risk of compressor overheating or damage. It is not recommended to attempt to override or bypass this fault. The unit should be kept off until the sensor fault is diagnosed and repaired.

Repair costs vary depending on the root cause. If only a connector re-seating or terminal cleaning is needed, a service call fee in the range of $75 to $150 may be the only cost. Replacing the discharge temperature sensor typically adds $50 to $150 in parts. If the outdoor PCB requires replacement, total costs including labor can range from $300 to $700 or more depending on the model and regional labor rates.

Some causes of E407, such as a disconnected sensor connector, can be addressed by a careful homeowner who is comfortable working around the outdoor unit with the power off. However, measuring thermistor resistance and inspecting wiring harnesses for damage requires a multimeter and basic electrical knowledge. Replacing a faulty sensor or PCB is best handled by a qualified technician, especially since the refrigerant circuit and high-voltage components are located in the same outdoor cabinet.

A power reset may temporarily clear the error code from the display, but E407 will return if the underlying sensor or wiring fault has not been corrected. Because the fault is tied to a measurable electrical condition in the sensor circuit, the board will detect it again as soon as the system attempts to operate. A reset alone is not a repair.