I am curious for Prius Gen 4, does the engine actually idle when it is operating with Battery or if the engine is completely shutdown ? I am just curious.
From these simulations, it appears to stop completely due to the nature of a planetary gearset: Toyota Prius - Power Split Device It definitely doesn't run at traffic lights, it's silent.
It is completely off. In some specific situations it might rotate dragged by the wheels or the electric motors without the usage of any fuel.
