Error 24 on the 850C means “Head light sensor error.” 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.
E-bike headlight
Match the light voltage your controller supplies. Your manual lists it.
Link coming soon
Electrical contact cleaner spray
Cleans dirt and corrosion from connector pins and battery contacts.
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 and your error history.