Code p0138 and p0161
 

Hey guys, I have a 2005 mustang gt and it’s throwing P0138 and P0161. I bought a o2 sensor and swapped it around first on pass side downstream then driver side downstream. Neither clears the code. Any suggestions?

That's the rear O2 sensor on the driver's side exhaust, first off, so that's your only concern, the rest aren't.

Second, if you've swapped out the O2 and are still getting these codes after replacement and erasing of codes, then the problem turns into wiring, grounds and/or battery/alternator issues. Since the others aren't popping a code, the battery and alternator are likely ok, and what you've gotten is a chafed wire and/or short, with a possibility of a connector/pin issue... and it may be at the computer end, or at the sensor end, or anywhere in between. You'll have to perform wiring diagnostics, which will require a wiring diagram and knowledge about what you should test and see. Tedious work, but that's where you'll need to go. Or have it done. You'll need a shop manual for the car or the online/CD/DVD equivalent.