I have my emissions light on my dash lit and am looking to replace the o2 sensor, however I have no idea whether it's the upstream or downstream one. Any suggestions on how to check? I was kind of tempted to just replace upstream and hope for the best, but any help would be great. I guess also, any ...

I have the emissions light on as well however I don't have a rough idle or stalling out of any kind. The emissions light is due to your o2 sensors not working (or maybe detecting some problem, but I think then the check engine light goes on). Either way, you can run a car with a faulty o2 sensor, ju...