Have a 2017 Sienna that would not move after stop for light. Seemed like transmission would not engage. No malfunction lights but heard grinding noise when finally able to get car to move.

If its a 2017 its under warranty, scheduled a service w/ a toyota service center and let them deal with it.

how to prevent the floor from moving when you have people going to the 3rd row seat?

Hi, had same problem with my Sienna se 2017, stopped for red, when switched to green, pressed gas and would not move, switched to reverse, pressed gas and same thing, no go, had it towed to dealer, no answer yet. There was also no warning lights of any malfunction on the display. What was worst is where I was stuck it was a two lane highway during morning rush hour. Police showed up quickly though.......