Shimano STEPS error E021: Battery not supported by drive unit
The drive unit recognises that a battery is connected and that the battery meets the basic system handshake, but it has concluded that the battery is not on the supported list for that firmware version. As a result the controller cuts motor assist, walk assist is unavailable and the display shows E021 until the mismatch is cleared. The bike will still roll unpowered, but no electric support is delivered.
| Drive system | Shimano STEPS (E5000, E6100, E7000, E8000, EP6, EP801) |
| Severity | Dealer needed |
| Keep riding? | Do not keep riding |
| Typical cost | If the diagnosis points to a firmware mismatch the dealer charges roughly 40 to 90 EUR for the update and bench time, while a non-supported replacement battery typically runs 500 to 950 EUR depending on capacity. |
Likely causes
- Aftermarket or non-original battery fitted that does not carry Shimano firmware IDs
- Battery firmware version older or newer than the drive unit expects after a software update
- Battery model from a different Shimano generation paired with an incompatible drive unit (for example an E8000 battery on an EP801)
- Replacement battery installed with the wrong part number during a previous service
- Corroded or contaminated contacts on the battery cradle breaking the authentication handshake
How to fix Shimano STEPS error E021
- Switch the system off using the battery power button, not just the display button.
- Wait at least 10 seconds, then switch the battery back on and check whether E021 clears.
- Remove the battery and inspect the contact pins on both the cradle and the battery pack; wipe clean with a dry, lint-free cloth.
- Reseat the battery, making sure it clicks fully home, then power the bike up again.
- Confirm the battery part number against the compatibility chart for your specific drive unit (E5000, E6100, E7000, E8000, EP6 or EP801).
- If E021 returns immediately, the battery is not supported by this drive unit - stop riding on assist and take the bike to the place of purchase or an authorised Shimano dealer for diagnosis.
Warranty: A genuine Shimano battery or drive unit that fails authentication inside the two-year warranty period is normally treated as a manufacturing fault and covered; water ingress, crash damage and pairing with non-original batteries are treated as non-warranty.
Typical cost: If the diagnosis points to a firmware mismatch the dealer charges roughly 40 to 90 EUR for the update and bench time, while a non-supported replacement battery typically runs 500 to 950 EUR depending on capacity.
Frequently asked
Can I reset Shimano error E021?
Yes, start with a full power cycle using the battery power button rather than the display. If E021 comes straight back the battery is genuinely not on the supported list for that drive unit and a reset will not hold.
Is it safe to keep riding with E021 showing?
The bike will roll without power, but motor assist and walk assist are disabled, so hills and heavy loads become much harder. Riding is not recommended beyond the short distance needed to get home or to a dealer.
What does E021 cost to fix and is it under warranty?
A dealer diagnostic and firmware update usually costs 40 to 90 EUR, while a replacement Shimano battery ranges from about 500 to 950 EUR. Genuine Shimano parts that fail inside the two-year warranty window are normally covered, but pairing errors and non-original batteries are not.
Related Shimano STEPS codes
Manuals and video
Official source: si.shimano.com
Not an official Shimano STEPS document. Compiled from workshop experience and public service information; details can differ per system version and bike brand.