Got Qubie back from the dealership. No more check engine light. Brand new oxygen sensor (and the gratifying thing is it’s exactly the one I thought it was supposed to be, so if I had replaced it on my own it likely would have solved the issues, too… yay).
Have to give props to Lafayette Ford in Fayetteville. They treated me kindly, corrected the problem, and treated Qubie well. That’s really all I can ask for, unless you include “I wish they were 60 miles closer.”
Photo is of Qubie out in my work parking lot. Figure I’d drive her directly in rather than trade cars to save time. Always fun driving her around :).