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Error code reference

Denso Air Conditioner Error Code E22

Circuit malfunction

Denso codesDenso air conditioner codes

Circuit malfunction — short or open in STI internal current/voltage detection circuit detected.

First step from the service manual

Replace the relay board, then initialize the fan motor.

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

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What E22 means on a Denso air conditioner

Error code E22 on a Denso air conditioner indicates a circuit malfunction in the STI (Smart Technology Interface) internal current and voltage detection circuit. The control system continuously monitors current and voltage levels through this detection circuit to protect compressor and fan motor components from damage caused by irregular electrical conditions. When the system detects either a short circuit or an open circuit condition within this detection path, E22 is triggered and normal operation is suspended to prevent further damage.

The STI detection circuit is integrated into the relay board, which serves as the central switching and monitoring hub for the unit's electrical loads. A short circuit in this path can result from insulation breakdown, moisture ingress, or a failed component on the relay board itself. An open circuit condition typically points to a broken trace, a failed sensing component, or a disconnected internal connector. Both fault types prevent accurate current and voltage readings, which the system treats as a critical protection failure.

The prescribed first diagnostic step is to replace the relay board, followed by initializing the fan motor. Fan motor initialization is required after relay board replacement because the new board must re-establish communication and calibration parameters with the fan motor controller. Skipping the initialization step after board replacement can result in the error persisting or new fault codes appearing, even if the relay board replacement was successful.

Source: manufacturer service documentation.

Common causes of E22

  1. 01

    Failed relay board

    Part replacement

    The relay board contains the STI current and voltage detection circuit. Internal component failure on the board, such as a shorted or open sensing element, is the most direct cause of E22 and is the primary replacement target in the diagnostic procedure.

  2. 02

    Short circuit in detection circuit wiring

    Wiring / connection

    Damaged or pinched wiring between the relay board and connected components can create a short that the STI circuit registers as a fault. Inspect wiring harnesses for visible insulation damage, burn marks, or contact with metal edges.

  3. 03

    Open circuit due to connector separation

    Wiring / connection

    A loose or disconnected internal connector on the relay board circuit path can produce an open circuit condition. Check all connectors seated to the relay board for secure engagement before proceeding to full board replacement.

  4. 04

    Moisture or corrosion on relay board

    Part replacement

    Water ingress or condensation buildup on the relay board can cause shorts between circuit traces or degrade sensing components. Look for corrosion residue, water staining, or oxidized contacts on the board surface.

  5. 05

    Fan motor not initialized after prior repair

    Wiring / connection

    If a relay board was previously replaced without completing the required fan motor initialization sequence, the detection circuit may report a fault due to mismatched calibration data. Performing the initialization procedure may resolve the code without additional parts.

See the test procedure for each cause

Frequently asked questions about E22

What does E22 mean on a Denso air conditioner?
E22 indicates a circuit malfunction in the STI internal current and voltage detection circuit, caused by either a short or an open circuit condition within that path. The STI circuit monitors electrical levels to protect key components during operation. When this monitoring circuit fails, the unit shuts down to prevent damage. The relay board is the primary component involved in this fault.
How do I fix error code E22 on my Denso air conditioner?
The recommended repair procedure starts with replacing the relay board, which houses the STI current and voltage detection circuit. After installing the new relay board, the fan motor must be initialized to allow the new board to establish proper communication and calibration with the motor controller. Skipping the initialization step can cause the error to persist even after a correct board replacement. This repair should be performed by a qualified technician familiar with the unit's electrical systems.
Is it safe to keep running my Denso air conditioner with an E22 error?
No, continuing to operate the unit while E22 is active is not advisable. The error indicates the internal circuit responsible for monitoring current and voltage levels is not functioning correctly, which means the system cannot detect electrical faults that could damage the compressor or fan motor. The unit typically suspends operation automatically when this code appears, which is the intended protective response. Leave the unit off until the fault is diagnosed and repaired.
Will resetting my Denso air conditioner clear error code E22?
A simple power reset is unlikely to permanently clear E22 because the fault points to a hardware failure in the relay board's detection circuit, not a transient software glitch. The error may temporarily disappear after a reset but will return once the unit attempts normal operation and the faulty circuit is active again. Proper resolution requires physical inspection and, in most cases, relay board replacement followed by fan motor initialization.
How much does it cost to repair a Denso air conditioner with error code E22?
Repair costs for E22 vary depending on parts pricing and local labor rates, but you should expect to pay for a replacement relay board plus the technician's time to install it and perform the required fan motor initialization. Relay board components for commercial or mini-split style units typically range from moderately priced to higher cost depending on the specific model. Total repair costs including labor generally fall somewhere in the range of a few hundred dollars, but obtaining a quote specific to your unit model is recommended.

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