The flex fuel sensor measures and senses the actual amount of ethanol content in the fuel that passes from the gas tank to the engine. This sensor detects the ethanol content by electrical charges and sends information to the ECM. This is applicable to your regal, xts, captiva sport, impala limited and suburban. The fuel flex sensor can easily be located underneath the rear driver side of the vehicle near the fuel tank. Safety measures in replacing the flex fuel sensor should be observed.