2017 Mercedes E220 Estate 4matic DRIVING POV/REVIEW // BETTER THAN THE AUDI A6? 

Start stop is disabled if your battery or auxiliary battery is low. Maybe a common situation if you are driving cars for sale that have stood around a while (or have an old aux battery). Also air conditioning has a priority over start stop. Kind Regards Matt

I think the start stop only works when you have the ac off I believe.