Is a car really sufficient cover from any grenade?

A flash-bang grenade is thrown in a parking lot. Somewhere else, in another identical parking lot, a fragmentation grenade is thrown. Can someone use a car as cover to completely avoid the effects of either explosion?

How does cover works in the case of a car used as cover? The rules say that a grenade doesn’t affect someone in cover unless it breaks the cover, and I cannot imagine the flash-bang grenade breaking the car — but at the same time, can the car really protect you from it? Similarly, I can’t imagine a car being fully destroyed by just a fragmentation grenade, so is it safe cover in that case?