So, I have 170,000 miles on my truck, and figured I'd change the original O2 sensors on my truck. I've always been under the impression that I have 2 (1 upstream + 1 downstream). But reading around, I'm starting to wonder if I have 4. Can anyone verify this for me without me having to crawl under the truck?

 

Well, I crawled underneath an discovered I have 2 cats, therefore I have (4) O2 sensors.. I should have done a little more research before asking..

 

2 cats indicate you have a California Emissions vehicle... thus yes you would have 4 o2 sensors.