View Here : What Is Flex Fuel
FHS: Vehicle Fuel Gasoline E85 (FlexFuel Truck) i believe the code is LC9 in the glovebox That was the RPO code for the all aluminum 5.3 engine in the GMT-900 trucks 2007-2013.
Flex Fuel - E-85 Ethanol. The most common of all fuels today is a 10% mixture of ethanol with 90% gasoline. The benefits of a Flex Fuel vehicle is that the fuel control systems in Flex Fuel vehicles adapts on the fly to whatever mixture of fuel is in currently the tank.