What does it mean?
Today, we’re accustomed to seeing the ethanol blends offered by refueling stations across the country. Almost every gallon of gasoline contains at least 10% ethanol (E10), an alcohol derived from corn stock, and most vehicles have no problems using it. Higher ethanol concentrations would be a problem for engines not calibrated to use it. Flex Fuel Vehicles can use up to 85% (E85) ethanol fuel.
Flex-fuel vehicles can use higher concentrations of ethanol, up to 85% (E85), but the engines are designed primarily to run on E10. To extract the most power most efficiently at any given time, the engine control unit (ECM) needs to know how much ethanol is mixed with the gasoline. The fuel composition sensor detects the amount of ethanol in the mix by detecting oxygen content (gasoline has zero oxygen), which can vary from 10-85%.
The ECM can adjust running parameters depending on ethanol content, resulting in smooth and efficient power output. Fuel Composition Sensor measures the oxygen content, directly proportional to the ethanol content, of the fuel. Aside from continually monitoring ethanol content in the fuel, the ECM also monitors the sensor itself for abnormalities in operation.
If the ECM detects a fault in the fuel composition sensor, it will set a diagnostic trouble code (DTC) in memory and illuminate the check engine light (CEL).