B is a selection on the gear lever on the CVT gearbox, I’ve used it on the Carolla and as rox says it uses engine braking and should be selected when going down a steep hill, the type where you see the ‘select low gear now’ sign. I would not think it would give better mpg, probably worse if anything. Don’t DSG gearboxes have this?
Daughters motability car Hyundai Tucson Ultimate self charging hybrid Serenity White Moss Grey interior.
My car SEAT Ibiza SE Tec 1.2 petrol TSI 2017.