I have a 2007 Nissan Altima hybrid and I always been puzzled by the computer algorithm that runs the ICU when I can see no need for it. One example is that the engine turns on at 40 mph even if I am coasting downhill. Why? There is certainly no need for engine power in that circumstance. Another example is that the engine runs until a certain engine temperature is reached. I guess that the engineers think that the drivers value passenger heat more than fuel economy. Why is the algorithm not set to turn the engine on only when the battery needs charging or when more power is needed than the battery can supply?