I'm on a family vacation right now and just drove 800 miles from the Bay Area to Seattle.
On our way through the Grants Pass mountain area in freezing temps, I stopped and filled up with Chevron Supreme. About 15 miles later, I get the CEL as I was using the manual shifter. The only thing that was immediately clear was my computer MPG readings dropped, even going downhill, but the engine power seemed to remain the same.
We weren't in a position to pull over, so I continued driving. After about 30 or so miles, my computer MPG readings seemed to normalize. We stopped in Portland for the night and this morning I took it to Autozone. They pulled a P0101 code, from what I gather this seems to be a MAF issue.
With it being Sunday and the car not in limp mode, I picked up the family at the hotel and decided to make our way to Seattle. But this time the code has cleared after I used about 13 gallons of the fuel from Grants Pass.
Is the CEL going to return? Could the fuel be the culprit? Is this a common issues with the XC90? I've researched this on this and other forums and I've found several instances of people bringing the XC90's in snow regions and getting CEL's, thought that was strange.
On the same note, I drove the tank from the Grants Pass Chevron near empty and filled again. I was averaging about 20mpg, so it doesn't seem the CEL really affected the MPG the computer was reporting. The overall MPG the computer reported was 18.1.