Hi everyone, I’m new to the forums so please feel free to give me tips or advice. I have an 08 type s and for most of the duration of me owning the car, it had a p0420 code. I took a long road trip after a few months with that code and two new ones popped up mid trip on the way back home, p0171 & p0174. I installed rv6 high flow cats and two new 02 sensors, one in bank one and the other in bank two. After a couple of weeks, the p0171 code came back, while the other two are gone. Then, after a day or two of say like 20-30 miles of driving it turned off by itself. After a few days of the CEL being off, but still being stored in the permanent code section according to my OBD scanner, I thought I would be safe to install the HPS Cold Air Intake. After the install, there was no CEL in the first start, or second start plus 10 minutes. Once I idled the car for a bit, turned it off, then on again about 20 minutes after installing the intake the p0171 code came back. One mechanic said I have to replace all my 02 sensors, but I can’t help but feel like that isn’t the problem. Thank you if you decide to help!

 

Which o2 sensors did you buy

 

I asked my mechanic, and I believe he said NTK (I asked a week or so ago) but he specified nothing cheap, as only Denso, Bosch, and NTK would do the trick. He also replaced only the affected sensors, another mechanic I used to go to claimed I should replace all four with Denso to get to solve the issue. Would a mechanic with a OBD scanner or a more sophisticated scan tool be able to directly pin point this issue? For more info, I cleared the code 3 days ago and it cane back the following day. Today, I cleared my code again before coming to work, so I’ll also update when the CEL inevitably comes back. After clearing the code I let my car idle for about 10 or so minutes, as I was also letting it warm up for a short drive to work.