Dear Sir:

This a common problem.
The main reason is worn belt in the deck. The electronic control every movement from the treadmill.

When the time, the worn cause many friction between belt vs deck, and the electronic design help the machine to shut down.... The reason for friction Enough is for lack of maintenance, specific for Lubricanting.
See the block diagram that I did for easy troubleshooting.
sincerely. God bless you.

ernesto a cuadra
managua, nicaragua. c.a.