P0420 (Catalyst System Efficiency Below Threshold (Bank 1)) - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

razman · 03-21-2022, 09:35 PM

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.)

Turdinator · 03-21-2022, 10:21 PM

Quote:

Originally Posted by razman

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?

FSFRS · 03-22-2022, 12:32 AM

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.

p1l0t · 03-22-2022, 10:39 AM

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.

Sent from my SM-G975U using Tapatalk

NoHaveMSG · 03-22-2022, 12:19 PM

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.

blsfrs · 03-22-2022, 01:40 PM

This is a good "bad cat" diagnosis video.

razman · 03-22-2022, 03:16 PM

Quote:

Originally Posted by Turdinator

Is you car stock?

Yes, it is completely stock.

zazashi · 11-07-2022, 07:53 AM

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!

03-21-2022, 09:35 PM	#1
razman Member Join Date: Feb 2018 Drives: 2013 frs Location: Los Angeles Posts: 10 Thanks: 0 Thanked 1 Time in 1 Post Mentioned: 0 Post(s) Tagged: 0 Thread(s)	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.)

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03-22-2022, 12:32 AM	#3
FSFRS Member Join Date: Mar 2022 Drives: '13 FR-S Firestorm Location: Houston Posts: 40 Thanks: 6 Thanked 89 Times in 29 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	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.

03-22-2022, 10:39 AM	#4
p1l0t Senior Member Join Date: Jan 2016 Drives: 2016 Subaru BRZ Hyperblue Location: West Hartford, CT Posts: 8,478 Thanks: 22,741 Thanked 9,438 Times in 4,847 Posts Mentioned: 58 Post(s) Tagged: 1 Thread(s)	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. Sent from my SM-G975U using Tapatalk

03-22-2022, 01:40 PM	#6
blsfrs Senior Member Join Date: Dec 2018 Drives: 2013 frs base Location: central Virginia Posts: 1,441 Thanks: 2,692 Thanked 1,451 Times in 686 Posts Mentioned: 13 Post(s) Tagged: 0 Thread(s)	This is a good "bad cat" diagnosis video.

11-07-2022, 07:53 AM	#8
zazashi Junior Member Join Date: Nov 2022 Drives: 2016 BRZ S Location: Stuttgart Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	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!

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