Error 14 on the 850C means “Motor's temperature sensor error.” Most likely cause: a damaged motor cable or connector, or a failed sensor. Try this first: turn it off and on again.
The motor's temperature sensor isn't reporting correctly. Its wires run through the motor cable, so check the cable and connector first. A failed sensor is a shop job.
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.
Motor extension cable
Replaces a damaged section of motor cable. Must match your connector and pin count.
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.