 Try to remember some of the basics of CQC. FlexFuel is just another name for ethanol, right? That's wrong! You can tune for a set percentage of ethanol without having FlexFuel, but if that percentage changes, then you have to change the tune. FlexFuel makes it happen automatically, and considering that E85 from the pump can vary by as much as 15%, and most people don't always use ethanol, FlexFuel means you can use one tune all the time, no matter how much corn juice is or isn't in the car. This is an ethanol content sensor. It measures the exact percentage of ethanol in the fuel. This is a Cobb FlexFuel module for a Subaru. It takes a signal from this and communicates with this. When you install all these in the car, a pro tuner can use custom FlexFuel tables in the tuning software to make a special tune. That tune can react in real time to the amount of ethanol in the fuel, so the tune adjusts itself as you drive. It's like friggin' magic.