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Error code reference

Mitsubishi Air Conditioner Error Code UF

USB host error

Mitsubishi codesMitsubishi air conditioner codes

USB host error - excessive current flows into the USB A connector.

First step from the service manual

Check if a USB device other than a USB memory device is connected to the USB A connector.

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

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What UF means on a Mitsubishi air conditioner

The UF error code on a Mitsubishi air conditioner indicates a USB host error caused by excessive current flowing into the USB Type-A connector. This connector is designed to accept USB memory devices for data logging, firmware updates, or configuration transfers. When the current draw through the USB port exceeds the threshold the host controller is designed to handle, the unit's protection circuitry triggers this fault and halts operation to prevent damage to the USB host controller circuitry on the main control board.

The most common trigger for this error is connecting an incompatible or power-hungry USB device to the USB-A port. The port is intended exclusively for USB memory sticks or flash drives, which draw minimal current. Devices such as USB hubs, charging accessories, hard drives, or other peripherals can demand far more current than the port is rated to supply. This overcurrent condition is detected by the host controller and immediately flagged as a UF fault.

In some cases, a faulty or damaged USB memory device can also cause excessive current draw even though it appears to be a compatible device. Additionally, if the USB port itself has suffered physical damage or a partial short on the control board, the overcurrent condition may persist even without any device connected. Diagnosing this fault correctly requires first ruling out the connected device before investigating the board-level hardware.

Source: manufacturer service documentation.

Common causes of UF

  1. 01

    Incompatible USB device connected

    Wiring / connection

    Plugging in a USB hub, hard drive, charger, or other high-current device instead of a basic USB flash drive is the most common cause. The port is designed only for low-power USB memory sticks.

  2. 02

    Faulty or damaged USB memory device

    Wiring / connection

    A defective USB flash drive can develop an internal short or malfunction that causes it to draw excessive current even though it looks like a compatible device. Try a different, known-good USB memory stick.

  3. 03

    Damaged USB Type-A port on the control board

    Part replacement

    Physical damage to the USB connector or a solder bridge on the control board can create a persistent overcurrent condition regardless of what is or is not plugged in. Inspect the port for bent pins, debris, or burn marks.

  4. 04

    Failed USB host controller on the main PCB

    Part replacement

    If the USB host controller IC on the main control board has failed internally, it may generate a false overcurrent signal or fail to regulate current properly. This condition persists even after removing all USB devices.

See the test procedure for each cause

Frequently asked questions about UF

What does UF mean on a Mitsubishi air_conditioner?
UF is a USB host error indicating that excessive current is flowing into the USB Type-A connector on the unit. The port is intended only for USB memory devices, and connecting an incompatible or power-hungry device will trigger this fault. The system flags this error to protect the USB host controller circuitry from damage.
How do I fix the UF error on my Mitsubishi air conditioner?
Start by unplugging any device connected to the USB-A port on the unit. If the connected device was not a standard USB flash drive, replacing it with a compatible USB memory stick should resolve the issue. If the error persists after removing all USB devices, the USB port or control board may have sustained damage and will require inspection by a technician.
Will resetting my Mitsubishi air conditioner clear the UF error?
A power reset may temporarily clear the UF fault code, but the error will return if the underlying cause has not been addressed. You must first remove or replace the connected USB device before cycling power. If the fault is caused by a damaged port or control board component, resetting alone will not resolve it.
Is the UF error on a Mitsubishi air conditioner dangerous?
The UF error itself is a protective fault, meaning the unit has already detected the overcurrent condition and stopped it from causing immediate harm. Continuing to operate the unit with a faulty USB device or damaged port connected could risk damage to the control board over time. Addressing the cause promptly is recommended to avoid more costly repairs.
How much does it cost to repair a UF error on a Mitsubishi air conditioner?
If the issue is simply an incompatible USB device, there is no repair cost beyond replacing the USB flash drive, which typically costs between $5 and $20. If the main control board has been damaged and requires replacement, repair costs including parts and labor can range from $300 to $700 or more depending on the unit model and service rates in your area.

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