Mid-Drive Bikes: How to Troubleshoot Speed Sensor Error 21

Applicable models: AGO e-bike (AGO X, AGO T, AGO Air), CARGO ONE, Longtail Duo
If the display shows Error 21 or a controller speed sensor error, it usually means the speed sensor is malfunctioning. When this happens, motor assistance will stop.

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Here are some simple steps to help you fix the issue:

1. Please check the rear wheel spokes. Ensure the magnet speed sensor is not missing. If it is missing, please contact our support team or your dealer for assistance.

2. - Verify that the sensor is correctly positioned on the spoke. Refer to the picture guide below for visual assistance.
- Pay attention to the distance (10–20 mm) and position of the magnet relative to the speed sensor.
- Align the magnet with the middle of the speed sensor.
- Use the appropriate torque (1.5–2 N.m) to secure the magnet in place.

3. If the issue persists after following the above steps, please reach out to our support team at [e-mail] or your dealer for further help.

WARNING: Refrain from trying to replace or install third - party components on your own, as this may void your warranty. We strongly recommend seeking professional help.