One problem related to crankshaft position sensor has been reported for the 2009 Mercedes Benz GL320. The most recently reported issues are listed below.
Mercedes benz Gl320cdi bluetec> shut off without warning while driving at the speed of 40 mph. Lost power steering and brakes and was nearly struck by another vehicle. An earlier version the 2008 model had the same experience on three occasions. Subsequently traded vehicle in for a 2009 model. Told by dealer part "crank shaft position sensor" is the cause. Part is being ordered from germany and would take at least a week. I suspect the part is in short supply due to frequent occurrences of this issue. A dangerous situation is lurking with this faulty sensor.