My check engine light is on and has been for a while now. My "at work son" checked it and said it was the 02 sensor and not to worry. I had my catalytic converter go out last year and was told at the shop that ethanol was very bad for your car motor. I've been buying 100% gas ever since. I live in a very small town with only 3 gas stations and they all have the option of 100% gas. It usually costs about 40 cents more than ethanol. I also get better gas mileage with 100% gas.