Error 21 indicates there is an issue with the amount of voltage or current being supplied to the internal controller and motor.

This can often be resolved by resetting the display, carefully removing the battery, inspecting the terminals, and re-installing the battery gently.

If the issue persists, the cause may be:

  • Internal controller (50%)
  • Motor (30%)
  • Battery (10%)
  • The wire from the motor to the controller (10%) - if it shows signs of damage at connections

Resetting your display to default

This is done from the main screen by holding the middle (Power) and top (+) buttons on your display at the same time. Select reset to default 'yes' and hold the middle button to enter that setting. These steps can be reviewed in our display tutorials:

Access to another bike

If you have access to another bike (with matching specs or components), you can test the motor easily or swap the internal controller, which could expedite the resolution. Check the following article for more info: Advanced troubleshooting steps.


Checking wires and connections 

Please take pictures where requested to share with our support team if necessary. 

This will likely resolve this issue faster. 

If you have checked your connections and reset your display without resolving the issue, please contact our support team for further assistance.