First let me say hello this is my first post. I have a 2001 with a 4 cyl and the check engine light came on today. I bought a code reader and the code that came up is po135. Could someone please help and tell me whitch one of the 2 o2 sensors this is? thanks for any help you can give.

 

That's the first one on the exhaust manifold in the engine bay, it's about $70.00 from autozone and usually pretty easy to replace if it's bad...

 

Thanks for the help