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Error code reference

Denso Air Conditioner Error Code E01

WMC room thermistor (RTS1) failure

Denso codesDenso air conditioner codes

WMC room thermistor (RTS1) failure — short or open detected.

First step from the service manual

Replace the WMC.

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

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What E01 means on a Denso air conditioner

The E01 error code on a Denso air conditioner indicates a failure in the WMC (Wireless Module Controller) room thermistor, designated RTS1. The control system has detected that the thermistor circuit is either shorted (resistance too low) or open (resistance infinitely high or out of range), meaning the unit can no longer obtain a valid indoor ambient temperature reading. Without accurate room temperature data, the air conditioner cannot regulate operation correctly and will fault out to protect the system.

The RTS1 thermistor is a temperature-sensitive resistor integrated into the WMC assembly. Under normal conditions, its resistance value shifts predictably with changes in ambient temperature, and the control board interprets these resistance changes as temperature readings. When a short occurs, the resistance collapses and the board reads an implausibly low temperature value. When an open occurs, the circuit is broken entirely and no signal is returned. Both conditions trigger E01.

Because the thermistor is embedded within the WMC unit rather than being a separately serviceable component, the prescribed first diagnostic action is full WMC replacement. Technicians should verify the wiring harness and connector between the WMC and the main control board before committing to parts replacement, as a loose or corroded connector can also produce an open-circuit reading that mimics thermistor failure. However, if wiring integrity is confirmed, replacing the WMC assembly is the correct corrective action.

Source: manufacturer service documentation.

Common causes of E01

  1. 01

    Failed WMC room thermistor (RTS1)

    Part replacement

    The thermistor inside the WMC assembly has developed an internal short or open, producing a resistance value outside the acceptable range. This is the most likely cause and requires WMC replacement.

  2. 02

    Loose or disconnected WMC connector

    Wiring / connection

    A connector between the WMC and the main control board that has loosened or partially pulled out can interrupt the thermistor circuit and generate an open-circuit fault. Inspect and reseat all connectors before replacing parts.

  3. 03

    Corroded or damaged wiring harness

    Wiring / connection

    Corrosion, pinching, or physical damage to the wiring between the WMC and the control board can cause intermittent or permanent open-circuit conditions that trigger E01. Inspect the full harness for visible damage.

  4. 04

    Moisture ingress into the WMC

    Part replacement

    Water or condensation entering the WMC housing can cause shorts across the thermistor circuit or corrode internal contacts, producing a shorted or erratic resistance reading. This typically requires WMC replacement.

  5. 05

    Faulty main control board

    Part replacement

    In rare cases, the input circuit on the main control board that reads the RTS1 signal may fail, causing it to incorrectly report a thermistor fault even when the WMC is functioning. This should be considered only after WMC replacement does not resolve the error.

See the test procedure for each cause

Frequently asked questions about E01

What does E01 mean on a Denso air conditioner?
E01 indicates that the WMC room thermistor (RTS1) has been detected as shorted or open by the control system. The thermistor is responsible for measuring indoor ambient temperature, and without a valid reading the unit faults and stops operating. The prescribed repair is replacement of the WMC assembly, though wiring and connectors should be checked first.
Can I fix the E01 error myself on a Denso air conditioner?
Checking and reseating connectors is within the capability of a knowledgeable DIYer, but replacing the WMC assembly involves working with electrical components inside the indoor unit. If you are not comfortable with appliance electrical work, a qualified HVAC technician should perform the repair. Attempting repairs without proper knowledge of the system can cause additional damage or personal injury.
Is it safe to run my Denso air conditioner while E01 is displayed?
No. When E01 is active, the unit has shut down because it cannot obtain a valid room temperature reading. Attempting to force the unit to operate without a functional thermistor can lead to improper temperature control and potential system damage. The fault should be resolved before resuming normal operation.
How much does it cost to repair a Denso E01 error?
Repair costs depend on whether the issue is a simple connector problem or requires a full WMC replacement. Labor charges for a service call typically range from $75 to $150 or more depending on your region. WMC parts costs vary based on the specific Denso model, but budgeting $100 to $300 for parts plus labor is a reasonable starting estimate for a full WMC replacement.
Will resetting my Denso air conditioner clear the E01 error?
A power reset may temporarily clear the E01 code, but if the WMC thermistor (RTS1) is genuinely shorted or open, the fault will return as soon as the unit performs its self-diagnostic routine. Resetting without repairing the underlying hardware issue is not a long-term solution. The root cause must be addressed to permanently clear the error.

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