There is no light, and as far as I am aware, there's not way to do this using forscan either. To know you have to activate the DPF % and watch it. Regen will start as soon as it hits 100%. You can turn on a manual regen toggle in forscan as well, where you can turn off auto regen if you're getting close to home with say a 95% full dpf, and don't want a regen to start. Ford decided that on these newer diesels, it was best that no one knows when it's doing a regen, for some reason.