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Error Code P0420


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I just had my exhaust installed a few days ago and havent had any issues until today. My Check engine light came on, So I went to Lexus and the ran a diagnostic on it and came back with a code error P0420 "Catalyst System Efficiency Below Threshold (Bank 1). They are telling me its because of the new exhaust.

I have search on the forum and havent found much help. Does anyone know how to fix this? The cats were removed is this causing the problem?

I have a 2006 IS350

Thanks for anyones help.

Mike

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I just had my exhaust installed a few days ago and havent had any issues until today. My Check engine light came on, So I went to Lexus and the ran a diagnostic on it and came back with a code error P0420 "Catalyst System Efficiency Below Threshold (Bank 1). They are telling me its because of the new exhaust.

I have search on the forum and havent found much help. Does anyone know how to fix this? The cats were removed is this causing the problem?

I have a 2006 IS350

Thanks for anyones help.

Mike

After reading that a few times I realized how obvious the answer is... Bartkat is right.... it thinks that something is wrong with the catalyst converter but you actually removed it... so that's it. Btw, how did Lexus not void your warranty?

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Yup, the CEL will turn on if you remove the primary CATs. Maybe high-flow aftermarkets would help but I don't know for sure.

I heard a rumor about people making some sort of electronic simulator to trick the car into thinking that the CATs are still installed.

However this is very illegal and I would not know anything about perpetrating such violent and hatful acts against our dear Mother Earth. :D

Regards,

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who put the new exhaust in? And how much of the exhaust was replaced? It sounds like you went from the headers back?

GHL Motorsports and they replaced from the "axle back".

And they removed the cats? Somethings not right here. Sorry. If they removed the cats, they put in more than an "axle back" exhaust system. The cats are way further up the line. And any even "semi" knowledgeable tech would know that you can't just delete the cats and put the 02 sensors back in and not throw a cel. The sensors before and after the cats read temp and nox gasses. That information goes right to the ECU and alters timing and a/f ratios to help compensate and maintain emmisions controls. Who is this GHL Motorsports place? Did they talk to you at all about this before they did the work?

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well, at this point, you have two choices, install 02 simulators or put the cats back in. What exhaust system did you put in? Tbh, I would put the cats back in. You not improving the air flow any by just removing those 2 cats. Unless a Mazzuri header is in your future also. Then I would do the sims ans you would need that anyway then. But if your not doing anything else to the exhaust, then I would just put the cats back on then.

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  • 2 weeks later...

I am in Australia and have the same issues. We replaced the whole exhaust system with stainless headers, new mufflers and larger diameter pipe and acheived the increase in performance we were after. We then had the same issue with the VSC light coming on with no cats installed so we then installed high flow cats and unfortunately still the same issue. Installing the original cats will fix the problem but then it will also delete the performance gains acheived by installing the sytem and high flows. The error can be easily reset but lasts for about a day then comes on again.

Woud love an answer to the problem as besides the lights being very annoying when driving, having the VSC work again when my wife is driving would be great. I love it not working though is it is awesome fun to drive sideways!!!

Any advice or help appreciated.

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