Lennox Air Conditioner Error Code E601

E601 indicates that the outdoor unit has been cycled off due to low temperature protection. This activates when the outdoor ambient temperature reaches or drops to -4°F (-20°C). It is a built-in protective function designed to prevent compressor damage in extreme cold. The unit will restart automatically when temperatures rise above the threshold.

Yes, the system is functioning as intended when E601 appears during extreme cold. The lockout is protective and prevents compressor damage. You should not attempt to override or bypass this protection, as running the compressor below -4°F can result in oil and refrigerant issues that cause permanent compressor failure.

If the error is caused by actual low outdoor temperatures, there is no repair cost involved. If a faulty outdoor ambient temperature sensor is to blame, sensor replacement parts and labor typically range from around $75 to $250 depending on the specific model and local labor rates. Control board replacement, if required, can range from $300 to $700 or more including parts and labor.

If outdoor temperatures are genuinely at or below -4°F, no repair is needed and the unit will recover on its own. If the error appears when temperatures are clearly above that threshold, the outdoor temperature sensor or its wiring circuit should be inspected. Sensor replacement and control board diagnosis are tasks best handled by a qualified HVAC technician.

A manual reset will not resolve E601 if outdoor temperatures remain at or below -4°F, because the control board will re-trigger the lockout immediately. The error will clear on its own once ambient temperatures rise above the low temperature cutoff point. If the code persists in warmer conditions, a sensor or wiring issue should be investigated.