Shimano STEPS Error Code E021 (Unsupported Battery): Meaning + What to Do
TL;DR
E021 = Battery conforms to system standards but is not supported by the system.
Official next step: Consult an agency/dealer (some manuals also note restarting).
Quick fix (safe DIY first)
- Restart the system (battery power switch/button).
- Confirm you’re using a supported Shimano STEPS battery for your drive unit generation.
- If the battery was recently replaced/borrowed, swap back to the original battery if possible.
60-second checks (the things that cause repeat codes)
- Did this start right after installing a different battery or after service?
- Is the battery genuine and intended for your STEPS system family?
What usually causes E021
- Loose or intermittent connectors (battery mount, motor harness, display/switch).
- Water/corrosion at contacts after rain/washing.
- Firmware/compatibility mismatch after service or a component swap.
- In some cases, an internal sensor or control-unit fault that needs dealer diagnostics.
When to stop DIY (go to a Shimano STEPS dealer)
Go to a dealer if:
– The code returns immediately after a clean restart.
– Assistance cuts in/out while riding (safety issue).
– You see damaged wiring, bent pins, corrosion, or water intrusion.
– The official remedy for the code is “consult an agency/dealer.”
Don’t do this
- Don’t force ‘compatibility’ with adapters—battery/DU pairing is safety-critical.
Related guides (closed-loop)
- Shimano STEPS error codes index: https://jieli-electric.com/shimano-steps-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/