Error 09 on the Bafang E170 / E180 / E181 means “Error with the engine phases.” Most likely cause: a damaged motor cable or a loose motor connector. Try this first: restart the system first.
The motor gets its power through three thick phase wires. This code means one of them, or the motor itself, has a problem. Often it's damage where the cable leaves the motor, or a loose connector. Because these wires carry high current, look but don't test-ride, and leave repairs to a shop.
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.