An oxygen sensor failed and many warning lights came on, most unrelated to what turned out to be the problem. This happened in a rural area and the car became sluggish to drive, but I managed to get to a mechanic who advised me that there are four of these damn things on the car. He said they're designed to improve fuel efficiency. I don't care about fuel efficiency, and now I fear the others may eventually fail, with a corresponding high cost to replace.