Exhaust Manifold Bolt Missing
 

I got a O2 sensor error (on the right side). I bought a pair of AC Delco replacements (just in case the other flaked out). Went to replace the one with the code this morning and found the manifold on that side is missing a bolt.

How likely is that to be the cause of the P code and will replacing that bolt correct the O2 sensor error ?

not likely. Do you have an exhaust leak there? you should replace it anyway

Other than it running a little rough I can't tell. The typical 'ticking' sound with an exhaust leak doesn't appear to be there, but then again it could be open enough that sound isn't obvious.

I'm gonna find a replacement bolt and get that taken care of too.

May not be leaking, but will sooner or later. Good idea to fix it
Cheap also

Any exhaust leaks that are upstream of an oxygen sensor, will cause the sensor to report a lean condition. The PCM will richen the fuel mixture, and your fuel mileage goes right down the toilet. One of the first things that an oxygen sensor DTC flow chart will instruct, is to check for exhaust leaks.

Good thing you found it out a bolt is missing, surely gonna do a mess soon.