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Error code reference

Denso Air Conditioner Error Code E02

Evaporator inlet air thermistor (RTS2) failure

Denso codesDenso air conditioner codes

Evaporator inlet air thermistor (RTS2) failure — short or open detected.

First step from the service manual

Reconnect the RTS2 thermistor and check the connection, then RESET the controller.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E02 means on a Denso air conditioner

The E02 error code on a Denso air conditioner indicates a fault with the evaporator inlet air thermistor, designated RTS2. This sensor is positioned at the inlet side of the evaporator coil and is responsible for measuring the temperature of the air entering the evaporator. The controller uses this data to regulate refrigerant flow, manage compressor cycling, and protect the system from freezing. When the controller detects either a short circuit or an open circuit condition in the RTS2 circuit, it triggers E02 and typically suspends normal cooling operation to prevent damage.

A short circuit in the RTS2 thermistor means the resistance has dropped far below the expected operating range, often to near zero ohms, causing the controller to read an abnormally high temperature signal. An open circuit means the resistance is effectively infinite, indicating a broken wire, failed thermistor element, or disconnected connector, which causes the controller to read no signal at all. Both conditions are outside the acceptable input range and are treated as sensor failures requiring attention before the unit will resume normal operation.

The first diagnostic step is to inspect and reseat the RTS2 connector, then perform a controller reset. Loose or corroded connector pins are a frequent cause of intermittent or persistent open circuit faults and can sometimes be resolved without part replacement. If the fault returns after reconnection and reset, the thermistor itself or the wiring harness between the sensor and the control board will need further testing with a multimeter to determine whether resistance values fall within the specified range for the measured ambient temperature.

Source: manufacturer service documentation.

Common causes of E02

  1. 01

    Loose or disconnected RTS2 connector

    Wiring / connection

    Vibration or handling during installation or maintenance can cause the RTS2 connector to work loose from its socket on the control board or harness. Reseating the connector and resetting the controller is the recommended first step and resolves the fault in many cases.

  2. 02

    Failed RTS2 thermistor element

    Part replacement

    The thermistor itself can fail internally due to age, moisture intrusion, or physical damage, resulting in either a shorted or open resistance reading. Confirm failure by measuring resistance across the thermistor terminals and comparing against the temperature-to-resistance specification for the RTS2 sensor.

  3. 03

    Damaged or broken wiring harness

    Part replacement

    The wiring between the RTS2 thermistor and the control board can develop open circuits due to pinching, chafing, or rodent damage. Inspect the full length of the harness for visible damage and use a multimeter to check continuity through each conductor.

  4. 04

    Corroded or contaminated connector pins

    Wiring / connection

    Moisture exposure at the RTS2 connector can cause pin corrosion that increases contact resistance enough to mimic an open circuit fault. Inspect the connector for green or white oxidation on the pins and clean or replace the connector as needed.

  5. 05

    Faulty control board input circuit

    Part replacement

    If the RTS2 thermistor and all wiring test within specification but the E02 fault persists, the thermistor input circuit on the control board may be damaged. This is the least common cause and should only be considered after all sensor and wiring checks are completed.

See the test procedure for each cause

Frequently asked questions about E02

What does E02 mean on a Denso air_conditioner?
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.
Can I fix the E02 error myself without calling a technician?
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.
Is it safe to run my Denso air conditioner while the E02 code is active?
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.
How much does it cost to repair an E02 error on a Denso air conditioner?
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.
Will resetting the controller clear the E02 error permanently?
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.

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