Ethanol sensors report the concentration of ethanol in your fuel. The sensor is typically installed on the return side of the fuel pressure regulator (i.e., between the fuel pressure regulator and the tank).

Due to variations in fuel system setup, the exact details of the physical installation will vary from one car to the next. So this page doesn't spend much time going over all those different options.

Instead, this page focuses on the theory and software configuration options supported in ECMLink related to running an ethanol sensor.