⚠ Scooter safety first
Segway's P65 handbook lists a recommended rider age of 18–60 years old. Always wear a helmet, and check your local rules for where scooters can be ridden.
Only do the safe checks on this page. Don't open the deck, battery, controller or motor. For anything else, contact Segway-Ninebot support or an authorized service center. About scooter codes on this site
⚠ Stop riding and get it checked This is a battery fault. Stop riding, don't charge it if it's hot, swollen or smells, and never open the deck or battery.
Quick answer
Error 21 on the Segway KickScooter P65 means “BMS communication error.” Most likely cause: a fault inside the battery or its management system (BMS). Try this first: switch off and restart.
Code meanings vary by brand. The same number can mean different things on different displays and controllers. Check your scooter's manual to confirm.
About the Segway KickScooter P65
From the Ninebot KickScooter P65 product handbook (model P65U). source Codes 11 to 13 say "phrase" in Segway's handbook. We kept the wording; it most likely means "phase". source
In plain English
The battery has its own management system that watches its cells, temperature and charging. This code means it found a problem. Never open the battery: contact support.
Step-by-step checklist
Reset
Work from the top. Steps go from free and easy to shop jobs. Switch the scooter off before touching any connector. Tick each step as you go. Your progress is saved on this device.
1 Switch off and restart Free Turn the scooter off, wait 30 seconds, then turn it back on. If the code clears, note what you were doing when it appeared, in case it comes back.
2 Check the outside of the deck (don't open it) Free Look at the outside only. If the deck is swollen or cracked, the charge port is wet or burnt, or it's very hot or smells, don't ride or charge it and contact support. If it smokes, get everyone out and call 911.
3 Write down the code and when it happens Free Take a photo of the display and note when the code appears: at switch-on, when you set off, on hills, in rain or while charging. Support will ask for this.
4 Contact support or a service center Shop job If the code stays after these checks, stop riding and contact the brand's customer support or an authorized service center. Don't open the deck, battery, controller or motor: most scooter batteries and controllers aren't user-serviceable.
⚠ When to stop and get a shop
Electric scooters keep the battery, controller and wiring inside the deck. Don't open the deck, battery or controller: most aren't user-serviceable, and a damaged battery is a fire risk. If these checks don't clear the code, contact the brand's customer support or an authorized service center.
Anything inside the deck, battery, controller or motor is a job for the brand's service center.
Still not fixed?
Pages to try next:
When it's time for a shop: if you've worked through every step and the problem is still there, contact the brand's support or an authorized service center. Bring your notes on when it happens, plus the code.
Words on this page: Controller BMS (battery management system)
Sources
Written and checked by Kazolt against the sources above. Last checked: October 23, 2026. How we write our fixes
Does Error 21 mean something different on your bike? Let us know so we can fix this page.