What Shimano says
The battery doesn't recognize the drive unit. (Shown as one flash of the battery's light.)
Shimano's recommended steps
- Use a genuine Shimano battery.
- Check the power cable.
- Contact your distributor or dealer.
Summarized from Shimano STEPS battery user manual (error E025), checked October 23, 2026. Follow the link for Shimano's exact wording.
If it keeps coming back
If the code comes back after one restart, stop using the assist and have the bike checked by a mechanic who works on Shimano systems. Bikes Plus has diagnostic tools for Shimano and most other major motor systems.
Write down the code and what you were doing when it appeared. That saves time at the shop.
Make sure it's a Shimano code
Error numbers mean different things on different systems. This page covers Shimano STEPS and EP e-bike systems. Codes starting with W are warnings, which clear when conditions improve; codes starting with E are errors, which point to a possible fault. Shimano's E-TUBE PROJECT Cyclist app can read the code from the bike.