Error 05 on the NIU KQi kick scooters (KQi2, KQi3, KQi3 Max) means “Controller over-temperature.” Most likely cause: the motor or controller got too hot from a long or hard ride. Try this first: let it cool down.
The scooter cuts or limits power when the motor or controller gets too hot. Let it cool down. If it overheats often on normal rides, have it checked.
Step-by-step checklist
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.
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.