[ovekvam]

Our F20 has manual transmission and dynamic cruise control. If I go downhill, and select a gear that just keeps the speed constant, the fuel consumption gauge shows zero. Fuel is cut, and the engine is just pumping air to spend the energy from the rear wheels.

If I engage the cruise control at this speed, the car is still going downhill at the same speed, but now the fuel consumption gauge is showing something like 5 L/100 km. That means the car is braking and applying throttle at the same time. Seems like a very stupid algorithm to me.

It also confirms my experience that if you want to keep the fuel consumption low, you need to stay off the cruise control. It also applies to much power going over crests, and brakes too much at the bottom of the hills.