Segway GT1/GT2 error code 21: Rear motor Hall sensor

What does this code mean?

No signal from the rear motor's position sensor.

Which models show it?

Segway SuperScooter GT1 and GT2

Safe checks you can do yourself

1. Switch the scooter off, wait 10 seconds and switch it on again; if the code stays, note it down.
2. Don't open the deck, battery or controller, and don't unplug cables yourself.

If the code stays after these checks, stop using the scooter and open a service request.