Would loose oxygen sensors cause PO171, PO174?
Both rear ones come loose regularly, and I retighten them regularly. I've checked and no pcv leaks, maf is clean, recent tune up, and fuel injectors cleaned.
Thanks.

 

No, only exhaust leaks before or at the front sensors would cause lean codes.

 

What do the codes tell you?
It's not the sensors that are the problem. They are only detecting it as the only way the system has to report the issue.
Description usually tells you 'lean'.
This means excess air passing through the motor for some reason, maybe like an air leak in the intake tract!
It can be from a lack of sufficient fuel but 99% of the time is not.
Good luck.

 

An exhaust leak before the front O2 can also trip a lean code.

 

You have to REGULARLY tighten the o2 sensors? I have never heard of such a thing. Do I need to get out more? Those sensors are usually seized in there. Are the exhaust bung threads damaged? Are the sensor threads damaged?

 

Yeah, I've never heard of a loose O2 sensor either.