P0420 (Catalyst System Efficiency Below Threshold (Bank 1))
 

My 2013 FR-S (73k miles; manual transmission) just threw this code for the very first time. I came across another thread on here (https://www.ft86club.com/forums/show...gen)%20sensors.) that discusses the issue but there was no resolution.

If you have dealt with this issue, was the converter the culprit or an O2 sensor? If the former, was "cleaning" it using one of those gas treatments helpful or did you simply have to replace it? Any thoughts on cost? (I'm in SoCal.)

Is you car stock?

I JUST had this code. at first, I cleared it myself, but it came back after 180 miles. I JUST finished installing a replacement oem header (with only 10k miles) that I bought off someone used for cheap who went catless tomei UEL.

The CEL went away right when I started the car up with the new header. Used my scan tool, code is still stored, but light is off. I can manually clear the code, but I want the PCM to make it go away on it's own.

I have 123k miles on my '13.

To my surprised, the previous owner of my car had a stock header on there without all the heatshields on it. He also didn't use original hardware and it seems like he had to weld a stud back on.... and worst of it all, he double gasketed the header to overpipe connection... I'm not sure if that was the curlpit, or the actual cat (the honeycomb looked fine inside), but I'm glad I atleast replaced that junk with a fresh oem header and new OEM subaru gaskets.

I gotta say, reinstalling a stock header is a bitch because of the studs that connect it to the overpipe. With aftermarket it's easier because there are no studs... had to drop the front pipe and disconnect the overpipe to do it.

It's one of those things that if you clear it and go through a drive cycle it might just go away. If it persists you may need to replace a cat or an O2 sensor(s). There is a way to emulate the signal of an O2 sensor with a resistor which is a cheap way of seeing if that is indeed the problem.

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Could be a few things, all a P0420 is cat efficiency. Could be bad cat, bad O2 sensor, or leaking exhaust gasket. I would check for an exhaust leak first, and check the O2 sensor second as a bad stock cat is not common.

This is a good "bad cat" diagnosis video.


https://www.youtube.com/watch?v=wrNtn3MkwG8

Yes, it is completely stock.

I got this too, from the beginning. I have BRZ S '16 with 53,000km. My house mechanic told me maybe we need to exchange the CAT with the manifold as I already let them switch the lambda but to no success.



Does anyone know if a 2018 GT86 Toyota cat with manifold fits for a 2016 BRZ S perfectly? I could get one below 300€ from an online site.



Thanks for the info in advance and best wishes!