Denso Air Conditioner Error Code E02

E02 indicates that the Denso controller has detected a short or open circuit fault in the RTS2 evaporator inlet air thermistor. This sensor measures the temperature of air entering the evaporator coil and is critical for safe system operation. When the signal falls outside the acceptable range, the unit logs E02 and interrupts normal cooling to protect the system. The fault requires inspection of the sensor, its connector, and the associated wiring.

Operating the unit while E02 is active is not recommended. The RTS2 thermistor provides temperature data that the controller uses to prevent evaporator freeze-up and manage compressor operation. Without a valid sensor signal, the system cannot protect itself from potentially damaging operating conditions. Keep the unit off until the fault is diagnosed and resolved.

A reset will clear the E02 fault code from the display, but if the underlying problem with the RTS2 thermistor or its wiring still exists, the error will return once the controller re-evaluates the sensor input. A reset is a valid first diagnostic step as directed, but it is not a repair. If the fault comes back after reconnecting the sensor and resetting, further testing of the thermistor and wiring is necessary.

The first step, reconnecting the RTS2 thermistor connector and resetting the controller, is something a knowledgeable homeowner or DIYer can attempt. Turn off the unit, locate the RTS2 sensor connector inside the indoor unit, reseat it firmly, and restore power to reset. If the error returns, further diagnosis requires a multimeter to test thermistor resistance and wiring continuity, which is better suited to someone with electrical troubleshooting experience.

If the fix is simply reseating a loose connector, there may be no parts cost, though you may still pay a service call fee ranging from roughly 75 to 150 dollars depending on your area. Replacing the RTS2 thermistor itself is generally an inexpensive repair, with parts typically ranging from 20 to 80 dollars plus labor. If the control board input circuit is damaged, board replacement is the most expensive outcome and can range from 150 to 400 dollars or more for parts and labor combined.