One problem related to mass air flow sensor has been reported for the 2009 Mercedes Benz C300. The most recently reported issues are listed below.
Ignition switch failed at 92,000 miles. Car was working fine and would not start again once parked. Dash lights & radio turned on, but car would not start. Horn did not work and gears would not shift with key turned on start position. Had to get car towed and cost $1,400 to fix. Aside from this, I have replaced the alternator, car computer, valve cover, and air flow sensor. Catalytic converters also went out, al within a 4 month period.