To those of you who have been following along with my salvage title auction G37 adventure, I thank you for not telling me the obvious solution (get rid of the car and find something else). I have been finding solutions to problems one after another so far, and now I am about at my wits end. Recently, I told you all how I had a decent size vacuum leak (which I was able to fix) along with some CEL codes for the downstream heated oxygen sensors. I haven't updated my other post, but I ended up taking my car to a mechanic for a diagnostic ($165) because I was at a loss for what the problem could have been. They tested the sensors themselves, the wiring from the sensors to the battery and ECU, everything was absolutely fine and in good working order. They then asked me for the part number of the O2 sensors I bought (226A0-JA10C), and that's where I realized my fatal mistake. I bought the wrong f*cking sensors. They then told me they can get two Denso heated O2 sensors for $200 a piece + tax, and around $76 for labor. My wallet is now officially empty and I am now starting to tap into my savings. Somebody please kill me

Here is what you all have been waiting for, the glorious list of new codes that showed up after driving to college and back:
- P0137
- P0139
- P0157
- P0159

I don't even know how to begin asking for suggestions. My old P0037 and P0057 codes, which were caused by having the wrong sensors installed, no longer show up but have been replaced with those codes after installing OEM quality sensors. If I take my car back, they most definitely will charge me for another diagnostic and labor to fix this $hit, I'm not even sure if they have a warranty on those sensors they installed. If someone has ever delt with these codes and successfully rectified the issue, please let me know what I can do in my situation before taking my car back to the mechanic and having a nice chat with him.

UPDATE 1: So I took my car back to the mechanic and had him examine the sensors that he installed (for free) and they found, again, that the sensors were working properly. They decided to tear down the car to expose the body harness to do a physical examination on it. What they found, while following Infiniti's wiring diagrams, was that the previous owner(s) did several repairs in multiple areas. They found wires that were installed backwards (pins in the wrong places). They ended up disconnecting what they could and reconnecting them to factory spec but after doing so, they got a timing solenoid code. They examined the timing solenoid I had and replaced it. Same problem. The car starts but it doesn't stay running for long with the wires connected properly. Now the shop is becoming as confused and depressed as I am since they had me pay for 3 hours labor and now they are keeping it over the weekend. At this point, I probably have already lost my mind since my reaction to this all is laughter :/

This is a long shot, but does anyone here have the slightest idea why connecting wires on the body harness backwards would fix any sort of issue on any vehicle? As I said earlier, connecting everything as Infiniti recommends is causing my car not to stay running. Any idea, or even a heartwarming post that won't help me with the car's issue but will give me the emotional support I need, will be immensely appreciated.

 

Once you get some money back into your wallet. Invest in a good OBD BT reader and Pro versions of Torque/OBD fusion.
This way you can monitor what your sensors are doing and further diagnose.
It's possible you have an exhaust leak/bad cat that gave you the initial issues and it's why the new sensors did not fix anything.
Leave the car without power for some time and repeat the searching for the codes, it's possible it will require a couple of drive cycles for them to go away.

Wiring has been "confirmed" to be in working order
Sensors are OEM denso brand new

You've confirmed the biggest issues/faults already. The remainder is to find out what are they actually doing and compare notes.

 

What do you mean by initial issues? Do you mean the four new codes that recently showed up?
Wouldn't a bad cat throw a P0420? And if it was a bad cat, wouldn't it only affect one of my sensors and not both at the same time (I'm not saying it isn't possible, more like it is highly unlikely that both cats are bad and throwing bank 1 and 2 codes simultaneously)? And my car did have several large exhaust leaks between the cats and the mufflers (loose bolts, very bad and worn out gaskets, etc.) but I repaired them over a month ago. It would be weird for problems related to exhaust leaks to show up after repairing the leak rather than before repairing them.
Also, replacing the sensors did fix the old codes (previously heater circuit low, banks 1 and 2), but now the new codes are confusing me (currently O2 sensor low voltage and slow response, banks 1 and 2). If the problem lies somewhere within my vehicle, wouldn't I have had these four new codes on my old sensors that I replaced, along with the heater low circuit codes?

In any case, thanks for the response