error code

ERROR 21: Speed Sensor Error

An Error 21 on your Display indicates an issue with your speed sensor.

There are a lot of bike wheel sizes and types out there, so installation of the speed sensor and magnet can vary based on your specific wheel. Below are steps in order to help you resolve your Error 21 issue!

Steps to resolve:

1) Check the distance between your speed sensor and magnet.

An error 21 is typically a simple fix and is due to improper installation and placement of the magnet in regards to the speed sensor. The magnet must be installed within 1-2mm of the speed sensor. Please reference the Installation Video on our website and follow the steps for installing the speed sensor and magnet within the proper placement.


2) Check the path of travel of your magnet in relation to your speed sensor.

The path of magnet travel must be directly perpendicular to the orientation of the speed sensor in order to properly operate.

3) Check the location of your speed sensor in relation to the rotation of your bike's tire.

Our recommendation is to install the sensor as far away from the center of the wheel as possible in order to help make sure that the magnet path of travel is as perpendicular to the speed as possible. In the image below the X represents where the speed sensor should not be installed (close to the center of the rim) while the green circle shows where the speed sensor should be installed (close to the outside of the rim).

4) Make sure that the Speed Sensor Cable was NOT yanked and pulled out of the Controller housing during installation and/or rough riding.

The speed sensor cables are actually relatively fragile and should not be yanked or pulled on (especially when being installed on bikes that should have speed sensor extensions in order to have the necessary length to function properly). It is not recommended to install these cables under tension as it can result in the cable being pulled from the controller. The only way to fix this would be to replace the entire controller. The speed sensor cable communication connection has narrow holes however if you suspect that the cable may have been pulled too tight during installation or use you can test for voltage from the controller by testing the voltage across the terminals as outlined in the photos below.

5) If you are reading power from the controller at the end of the Speed Sensor Extension cable and none of the other steps above resolved your Error 21 issue then the final step would be replacing the Speed Sensor itself!

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