E10 on the Velotric (Discover, Nomad, Summit, Fold, Breeze, Triker, T1, GoMad, Tempo) means “Photosensitive Sensor Abnormality.” Most likely cause: a problem with the light sensor or its wiring. Try this first: turn it off and on again.
Some displays can switch the lights automatically using a light sensor. This code means that sensor, or the light circuit it controls, isn't reporting correctly.
Step-by-step checklist
Work from the top. Steps go from free and easy to shop jobs. Switch the bike off before touching any connector. Tick each step as you go. Your progress is saved on this device.
Parts you might need
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Only buy a part if the free steps didn't fix it. Always match the voltage and connector type to your bike.
Rechargeable bike light set (USB)
The simplest fix if your built-in light has died: a self-powered light that needs no wiring. To replace the built-in light instead, match the voltage your controller supplies (your manual lists it).
When it's time for a shop: if you've worked through every step and the problem is still there, take the bike to an e-bike shop. Bring your notes on when it happens, plus the code.