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Error 21

Xiaomi Electric Scooter

Severity:

Source: OnlyErrorCodes.com — Every error code. One place.

Xiaomi Scooter Error 21 — What It Means & How to Fix

What Does This Error Mean?

Xiaomi scooter Error 21 indicates a main controller (ESC) fault. The scooter will typically refuse to accelerate. Start with a full power cycle and firmware update — if the error persists, the controller board likely needs replacement.

Affected Models

  • Xiaomi Mi Electric Scooter
  • Xiaomi Mi Scooter Pro
  • Xiaomi Mi Scooter Pro 2
  • Xiaomi Mi Scooter 3
  • Xiaomi Mi Scooter 4 Pro

Common Causes

  • Firmware corruption in the motor controller (ESC)
  • Overheating of the ESC after extended high-speed riding
  • Water ingress into the controller housing causing a short circuit
  • Hall sensor fault in the motor — controller cannot read motor position
  • Physical damage to the ESC board from a drop or impact

How to Fix It

  1. Perform a full power cycle.

    Hold the power button for 5 seconds to fully shut down the scooter. Wait 60 seconds, then power back on. A transient ESC firmware glitch can cause Error 21 and a cold restart often clears it.

  2. Check for recent water exposure.

    Xiaomi scooters have limited ingress protection. If the scooter was ridden in rain or through puddles, water may have reached the ESC. Remove the deck panel screws and allow the interior to dry for 48 hours with the scooter stored in a warm, dry place.

  3. Update the firmware.

    Connect to the Mi Home app and navigate to the scooter's firmware update section. Install the latest available firmware. Firmware updates can fix ESC communication bugs that trigger Error 21.

  4. Allow the scooter to cool completely.

    If Error 21 appeared after extended riding at high speed, the ESC may have thermal-throttled and triggered the fault. Leave the scooter off in a cool, shaded area for 30 minutes and retry.

  5. Inspect the motor connector.

    On the underside of the scooter, trace the motor cable to the controller housing. Check that the connector is fully seated. A partially disconnected motor connector causes the controller to report an error because it cannot read Hall sensor signals.

When to Call a Professional

If Error 21 persists after a firmware update and full power cycle, the ESC board needs professional diagnosis or replacement. Take the scooter to a Xiaomi service center.