LG Heat Pump Error Code t4

The T4 error code indicates a fault in the liquid refrigerant pipe temperature sensor at the condenser outlet. The PCB has detected a voltage signal outside the valid range, either above 4.9V (open circuit, below -50 degrees C) or below 0.4V (short circuit, above 93 degrees C). This typically points to a disconnected connector, a failed thermistor, or a damaged wiring harness. The system halts operation when this fault is active to protect the refrigerant circuit.

The heat pump will generally lock out operation when T4 is active, so continued running may not be possible without clearing the fault first. Attempting to bypass or ignore the error is not advisable, as the condenser outlet sensor provides data the control system relies on for safe refrigerant management. Address the fault before resuming normal operation.

Repair costs vary depending on the root cause. Replacing a thermistor sensor typically involves parts costs in the range of 20 to 80 dollars plus labor, while a wiring harness repair may add additional labor time. If the control PCB requires replacement, total costs can range from 300 to 700 dollars or more depending on the unit and labor rates in your area. Diagnosis by a certified technician is the best way to get an accurate estimate for your specific situation.

A knowledgeable DIYer can perform initial checks such as reseating the sensor connector at the PCB and visually inspecting the wiring for obvious damage. Resistance testing with a multimeter is also straightforward if you have access to the sensor terminals and the correct resistance table. However, if the sensor needs replacement or the PCB is suspected, a qualified HVAC technician is recommended, especially since accessing internal refrigerant system components may require certification.

A power reset may temporarily clear the T4 fault display, but the error will return if the underlying sensor or wiring issue has not been resolved. The PCB continuously monitors the sensor voltage during operation, so any persistent open or short circuit condition will re-trigger the fault shortly after restart. A reset is useful for confirming a repair was successful, but it is not a fix on its own.