Bafang · Speed signal
21 Bafang error code 21
Speed sensor fault
Per manufacturer documentation
Note
Meaning may depend on model, display and firmware – verify with the manual of the exact type.
Possible causes
General, component-based causes – not a manufacturer-specific statement.
- Spoke magnet moved/missing
- Speed sensor gap/cable
- Wheel size setting
Safe test steps
- Does the magnet pass the sensor, gap (manufacturer value, often a few mm).
- Cable damage along the chainstay.
Workshop reference values
- No general documented measurement value – manufacturer service documentation required.
Repair approach
- Align magnet/sensor, repair cable; set wheel size correctly.
Tools needed
- Basic hand tools, insulated screwdrivers
- Digital multimeter (CAT III, fused inputs)
Safety
- Tampering with the speed signal may be illegal and can lock the system.
This information does not replace manufacturer service documentation. Work on batteries and high-voltage parts only with the appropriate expertise.