 That's probably what's happening on the vehicle. Most people, if you've got a catalytic converter that has had multiple failures like that, if it's not clogging up but it's turning the light on, they'll just leave it and they'll drive it that way as long as the vehicle is still operating well. But you've got to check engine light, unfortunately. But if it's burning oil, that's what's happening. Now, on the other hand, with the oxygen sensor failing, typically it's the heater that fails in the sensor.