LG Air Conditioner Error Code 158

Error code 158 on an LG air conditioner signals that the low pressure sensor on the sub3 outdoor unit is reading as open-circuit or short-circuit. This means the control board cannot get a valid pressure reading from that sensor. The system flags this fault to prevent operating under unknown refrigerant pressure conditions, which could cause compressor damage.

It is not advisable to continue running the unit while this fault is active. The low pressure sensor protects the compressor from operating under low refrigerant pressure conditions, and without a valid sensor reading, the system cannot provide that protection. Continued operation could result in compressor damage, which is a significantly more expensive repair.

A power reset may temporarily clear the fault code, but if the underlying sensor or wiring problem still exists, the code will return once the unit restarts and the PCB re-checks the sensor signal. A reset alone is not a repair. The sensor connection, wiring, and sensor condition must be properly diagnosed and corrected to permanently resolve the fault.

A knowledgeable DIYer can start by checking whether the sensor connector is fully seated at the outdoor unit PCB, which requires no special tools. If the connector is secure and the error persists, diagnosing the sensor and wiring with a multimeter is the next step. However, if the sensor or PCB needs replacement, a certified HVAC technician should handle the repair, especially since the outdoor unit involves refrigerant circuits.

If the issue is just a loose connector, the repair cost may be limited to a service call fee, typically in the range of $75 to $150. Replacing the low pressure sensor itself can cost between $100 and $300 including parts and labor. If the outdoor unit PCB requires replacement, costs can range from $300 to $700 or more depending on the unit model and labor rates in your area.