LG Heat Pump Error Code E343

E343 indicates a fault with the SUMP TEMP FIXED 2 sensor in the outdoor unit, triggered by a signal voltage above 4.95V (open circuit, reading below -30°C) or below 0.5V (short circuit, reading above 151°C). The error is only activated when outdoor temperature is above -10°C. It means the control board cannot receive a valid temperature reading from this sensor, so the system stops normal operation to prevent damage.

It is not recommended to attempt to bypass or ignore the E343 error. The SUMP TEMP FIXED 2 sensor provides data the system uses to protect the compressor and manage refrigerant. Operating without a valid sump temperature reading could lead to compressor damage or refrigerant issues. The system is designed to stop operation when this fault is detected, and that safeguard should be respected.

Repair costs vary depending on the root cause. If only a connector needs cleaning and reseating, costs may be limited to a service call fee, typically in the range of $75 to $150. If the NTC thermistor sensor requires replacement, parts and labor combined can range from $150 to $400 or more depending on your region and the specific model. Wiring harness repairs fall somewhere in between depending on the extent of the damage.

Some aspects of diagnosing E343 are accessible to a knowledgeable DIYer, such as visually inspecting the outdoor unit wiring harness and reseating connectors. However, testing sensor resistance, tracing wiring faults inside the unit, and replacing components on a heat pump system typically requires familiarity with refrigerant systems and electrical diagnostics. For most homeowners, a qualified HVAC technician is the safer choice.

A power reset may temporarily clear the E343 error code, but if the underlying sensor or wiring fault is still present, the error will return once the system runs and the outdoor temperature is above -10°C. A reset is useful as part of diagnosing whether the fault is intermittent, but it does not repair a broken sensor, failed thermistor, or damaged wire.