E-Bike Motor Stuttering (Bafang C961)

In plain English

A hub motor needs all of its power wires and position sensors working to run smoothly. If one is damaged or loose, often at the axle or the motor connector, the motor judders, especially when starting from a stop. It may make a grinding noise even though nothing mechanical is wrong. Loose battery connections can cause a similar pulsing feeling.

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.

1. 1Turn it off and on againFree Switch the display off, wait 30 seconds, then switch it back on. If the code clears, note what you were doing when it appeared, in case it comes back.
2. 2Look over the motor cableFree Follow the cable from the motor along the frame. On hub motors, look closely where it leaves the axle: it often gets pinched when the wheel is removed or crushed when the bike falls. Look for cuts, kinks or bare wire.
3. 3Reseat the batteryFree Switch off and slide or lift the battery out of its mount. Wipe any dirt off the metal contacts on the battery and the mount, then put it back until it clicks and locks.
4. 4Unplug and check the motor connectorEasy Switch off and remove the battery. Follow the motor cable to its plug (often near the rear axle or under the frame). Pull it apart, look for bent or pushed-back pins, water, corrosion or burn marks, let it dry, then push it back together firmly.
5. 5Wiggle-test the wiringEasy Lift the motor wheel off the ground. With the motor running gently at low assist, wiggle each connector and cable one at a time. If the motor cuts out or the code appears, you've found the loose spot. Switch off before reseating it.
6. 6Dry the bike out if it got wetModerate If the problem started after rain or washing, remove the battery and leave the bike somewhere warm and dry for 24 to 48 hours, then test again.
7. 7Have the motor testedShop job If the cable and connector look fine, a shop can test the motor's wiring and sensors. Opening a motor or working on its high-current wires is a shop job.

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.

• Electrical contact cleaner spray

  Cleans dirt and corrosion from connector pins and battery contacts.

  Link coming soon

• Dielectric grease

  A thin coat on connector seals helps keep water out after you clean them.

  Link coming soon

• Motor extension cable

  Replaces a damaged section of motor cable. Must match your connector and pin count.

  Link coming soon