How long do O2 sensors last and how do I know they have gone bad? I have a little over 80K on my car and I have noticed my gas mileage has very recently decreased. I realize it might be because of the A/C increase during the summer, but it has never been this bad in the past. Should my car throw a CEL if one has gone bad?

 

If your O2 sensor has gone bad it tends to turn on the check engine light.

 

^ thanks