Aventon error 21: Speed sensor error
Aventon e-bikes with Bafang hub motor (Pace, Level, Aventure, Sinch, Soltera) and Aventon colour or LCD displayFix at homeRide with caution
No wheel speed signal reaches the controller. Speed reads 0 and assist cuts out or is limited. On Aventon bikes the sensor sits on the chainstay with a spoke magnet on the rear wheel, and the magnet moving is the usual cause.
Likely causes
- Spoke magnet moved or too far from the sensor
- Sensor misaligned or cable loose
- Water in the connector
- Faulty sensor
How to fix Aventon error 21
- Align the magnet 2-5 mm from the sensor; tighten it
- Check the sensor connector; dry and re-seat
- Spin the wheel with the display on to confirm speed registers
- Replace the sensor and magnet
Go to a dealer if: Go to a dealer if a new sensor still gives 21.
Warranty: Aventon gives a 2-year limited warranty on frame, motor, battery and electronics through its dealer network; open a ticket with Aventon support before replacing parts.
Typical cost: Sensor and magnet about USD 15-25; usually free.
Warranty: Aventon gives a 2-year limited warranty on frame, motor, battery and electronics through its dealer network; open a ticket with Aventon support before replacing parts.
Typical cost: Sensor and magnet about USD 15-25; usually free.
Still stuck? Take a photo of the display and show it to a local e-bike workshop. Bring the bike's system name (e.g. Bosch Performance Line CX) and the exact code; that saves diagnostic time and money.
Frequently asked
How do I reset Aventon error 21?
Fix the magnet gap and power cycle.
Can I keep riding?
Yes, with limited assist.
Warranty?
A moved magnet is not a defect; a failed sensor is covered.
Related Aventon codes
Not an official Aventon document. Compiled from workshop experience and public service information; details can differ per system version and bike brand.