I’m not Rick or any of the other mechanics, but until they come along, I hope I will do.
I don’t think you’ve done much harm to your car. You’ve probably just freaked out the engine monitoring system because it’s noticed a loss of efficiency. Now if you’d put normal gas into an engine designed for E85 (ie. done the opposite), you might have a problem. But in your case, I think it’s ok.
I’d wait for confirmation from one of our mechanic dopers before I visit the dealer, if I were you. It might transpire that you haven’t hurt the car, but they will use it as an excuse to screw you out of your warranty anyway.
Note that the E85 may loosen some of the crap (rust, dirt, etc.) in your fuel system, especially if you have an older car, and burn straight gasoline (as opposed to gasohol) on a regular basis. Replacing the fuel filter may not be such a bad idea – they’re cheap and usually easy to change.
We discussed this issue before, here at the Dope, and The consensus is that filling your tank with E85 once, will not do any damage to your engine. Doing it often will cause problems. Here in Denver, you get some Ethanol with every fill up any way.
As for the reverse, putting regular gas into the tank of a car designed for E85? Well, they call it a “flex-fuel” vehicle for a reason. They allow flexible fuel mixtures, ranging from 0% ethanol (pure gasoline to 85% ethanol (E85).
I judged a science fair yesterday where a student studied the long term effects of E85 on various types of fuel lines (they softened, eventually). It was a great project, even though I think his dad did most of it (by his own admission on the poster board). This was a 6th grader! Dopers, there is hope for the next generation. Maybe.
Thanks to the wonders of the internet, I found this (pdf):
“What happens if I accidentally fuel my gasoline-powered vehicle with E85?
According to the National Ethanol Vehicle Coalition, no problems should occur if you mistakenly fuel once with E85. The “check engine light” may appear due to the higher oxygen content in E85. Long-term use of E85 in gasoline-only vehicles may cause damage because of the incompatibility of high-ethanol blends with parts in gasoline-only engines. Alcohol fuels can be more corrosive than gasoline. Therefore, fuel system parts have been upgraded to be ethanol-compatible. Also, improper use of E85 may compromise performance and emissions. For instructions on how to read a vehicle identification number to determine if your vehicle is E85 compatible, go to www.e85fuel.com/information/vin.php”
To get rid of the check engine light, take the leads off the battery and let your car sit for, oh, I don’t know, 10 minutes or so. Check engine lights usually have nothing to do with the engine going tits up, it’s mostly a system that warns about inefficiency, oxygen sensors, emissions, timing being off, etc. It doesn’t mean “OH NO WE’RE ALL GOING TO CRASH”, even though that’s what I feel like every time I see one.
Another way to make a warning light go away (as practiced by one of my wife’s college classmates on the new Volvo her daddy just bought her) is to put a bandaid over it. Apparently, the oil light was ‘bugging’ her with its constant irritating glow. Not surprisingly, the engine eventually seized up due to lack of oil.