Denso Air Conditioner Error Code E05

Error code E05 on a Denso air conditioner indicates a fault with the evaporator pipe inlet thermistor, identified as CTS2. This sensor is mounted at the inlet of the evaporator coil and continuously monitors refrigerant or pipe temperature to help the controller manage cooling cycles, prevent coil icing, and protect the system from operating outside safe temperature boundaries. When the controller detects a signal from CTS2 that falls outside the expected resistance range, it registers the fault as either a short circuit (resistance too low) or an open circuit (resistance too high or no signal at all), and shuts down or restricts operation to protect the system.

The most common triggers for E05 are a loose or disconnected wiring connector at the thermistor, damaged wiring along the harness between the thermistor and the control board, or a failed thermistor element itself. Thermistors are NTC (negative temperature coefficient) components, meaning their resistance decreases as temperature rises. A short circuit typically reads near zero ohms regardless of temperature, while an open circuit reads infinite resistance. Either condition produces a signal the controller cannot interpret as a valid temperature, triggering the fault.

The first diagnostic step is to physically inspect and reseat the CTS2 connector, then perform a controller reset to determine if the fault clears. If E05 returns after the reset, the thermistor wiring and the sensor itself should be tested for continuity and correct resistance values. If the wiring and connector check out, the thermistor likely requires replacement. In some cases, moisture ingress or corrosion at the connector pins can cause intermittent contact issues that mimic a hard sensor failure.