Bafang E-Bike Error Code 21: Meaning + Fix Checklist
TL;DR
Error 21 = Speed sensor error.
Official guidance (Bafang): Restart; align spoke magnet 10–20mm; check connector; BESST signal check; update controller; replace sensor; else controller.
Note: Bafang error codes can vary by display/system (UART vs CAN, model families). This page follows Bafang’s official DP C271 display manual wording.
Quick fix (safe DIY first)
- Restart the system.
- Check the magnet is present and passes the sensor at the correct gap (manual notes 10–20 mm).
- Re-seat the speed sensor connector and ensure it isn’t damaged.
- If it persists, a shop can test sensor signal and controller.
60-second checks (what causes repeat codes)
- Power off → on again, then re-check.
- Inspect visible connectors (display/controller/battery area) for loose, wet, corroded, bent pins, or damaged cables.
- If the code appears after rain or washing: dry the bike and avoid pressure washing around the motor/battery mount.
Common causes
- Magnet misalignment/missing.
- Loose sensor connector.
- Sensor failure.
When to stop DIY (go to a shop)
Go to a qualified e-bike shop if:
– The code returns immediately after a restart.
– Assistance cuts in/out while riding (safety issue).
– You see damaged wiring, corrosion, or water intrusion.
– The official fix references dealer tools (e.g., BESST) or component replacement.
Related guides (closed-loop)
- Bafang error codes index: https://jieli-electric.com/bafang-e-bike-error-codes/
- E-bike error codes hub: https://jieli-electric.com/e-bike-error-codes/
- Speed & power thresholds: https://jieli-electric.com/speed-power-thresholds/
- Laws & Safety Hub: https://jieli-electric.com/laws-safety/