Thanks. You are right, it is very unlikely that they would all go at once. I replaced all O2 sensors, just to get them over with at the same time. I had a CEL before and the codes pointed to two O2 sensors. I just did all of them at this time to be done with it. This was unrelated to the heater problem. Just wanted to let people know how to fix that. My main problem right now is the 420 and 430 code. I know it is not the O2 sensor because they are new. Must be the cat?
