A few weeks back I went to the gas station and they were out of everything but premium gas. So, I got to fill up on premium at the same price as regular. I think the premium may have been 93 octane. Within 2 or 3 trips my previously lighted "Check Engine"light went off. Yay!
Next fill up was with regular gas, and the “Check Engine” light came on again.
A few days ago I filled up with an ethanol blend with a 91 octane rating, vs. 89 normal, and voila! The “Check Engine” light went off again after a few trips.
Correlation, or chance? And if there’s a correlation what sensor: oxygen? (The gas cap was properly secured in all situations.)
Ethanol is somewhat corrosive and can have a detergent effect on the engine. Very high octane gas in Canada (Sunoco 94 in the East, or Mohawk/Husky 94 in the West) are ethanol blends, since ethanol has a higher octane rating than dino juice. I also understand that in Eastern Canada it is common practice to use very poor quality fuel for “regular”, with a dose of ethanol to boost the low octane rating to 89, and this is marked on the pumps, but I’ve never been there. In the west, Husky/Mohawk is the only brand that uses ethanol.
Just because the cap was “secure” does not mean its not related. It could be loose for example. My light comes on everytime ifill up and my cap is always “secure”
We’ve done this before. If you car requires premium fuel, and you run regular, it can cause engine knock and misfire. Modern engine management systems will detect misfire and can and will illuminate the check engine light for a misfire. Modern systems also have the ability to turn out a check engine light if the problem no longer exists.
You did not mention year make or model, so all the above is a wild assed guess.
