I have had my beloved stylin' minivan into the shop 3 or 4 times because of this "check engine" light on my dashboard.
As tempted as I am to ignore it, I always end up back at the dealer, asking them to check and make sure nothing is amiss.
This time, apparently, my minivan is under the (mistaken) impression that the external temperature is -40 degrees. (shrugs) And furthermore, apparently, this can affect my gas mileage. (shrugs)
So, next week, guess who will be taking her 'baby' back to the shop? (rhetorical)