Code trouble

[fejwe]

I searched on all of this, and while there were people with similar codes, I didn't see the same question twice:

I've been getting P0156 and P0161 repeatedly. I changed the Driver's side back O2 sensor and added MIL eliminators and I'm still getting the code. Does this mean that I somehow broke the new o2? Or should I try to switch them (I have this totally bizarre cobbled-together exhaust, and pulling the passenger side one is a total pain, so I'd like to avoid that). Is there something else going on with the car that would be killing the O2s, like a short or something?

Thanks, and sorry for another code question
T

 

[STAMPEDE3]

Swap the mils from side to side and see if the code follows.
If it does it is the mil.
If it doesn't it is the O2.