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Discussion Starter #1
I've read, never tried, about the O2 sensor spacer trick to fool the ECU into thinking the cat is working properly. I have a Magnaflow system on my car with a high flow cat and I have a P0420 code. My first question is has anyone done this trick and not experienced any problems afterwards? And my second is how will this affect my car during the state mandated emission testing to register my car for new tags? Thanks in advance.
 

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I have had this code before on a CA emissions sentra and it can become a pain. To pass emissions testing, no cel should be illuminated or automatic fail. They also test your evap system by drive cycles, we do that at our work.

To trick the o2 after cat sensor, you need to have it detect CO and O2 based upon voltage readings. If you were to trick the PCM, you would need to get a spak plug anti fouler, then possibly rethread it to fit the o2 and give it just enough to read correct 02 flow. Your code is telling the PCM that your cat converter is basically "toast". Another method I have heard from on here is to get a pcm tune performed to ignore the rear o2. I strongly suggest you just replace the cat and rear o2 together. The 2 alternatives I mentioned to trick it is nothing more than a "band aid" to a deep cut wound. They may come back or cause future issues. From a tech perspective, replace the cat and rear o2 sensor and have the pcm reset of codes.
 

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I understand that the best option is to replace the cat in the least, but I have a full exhaust system and at the time I'm unsure if I can replace the cat or possibly weld another in. If any case I'll have to get another high flow cat and it'll probably not fix the issue. My only concern until I can get it properly fixed, is if I do this, I've heard that on other cars, after doing this mod the car experiences a rougher idle and decreased mileage. Will this also be the case with the cobalt? And if I do this mod and it fixes my problem, if I were to go in for inspection, will they check and find the adapter, causing more problems?
 

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Yeah I believe I do. I bought the car with the light on and with the exhaust.

---------- Post added at 07:51 AM ---------- Previous post was at 07:48 AM ----------

Fact is that I don't know if it even has a cat, but I do know its a full Magnaflow system.
 

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Yes I've been up under the car and I noticed a very small "cat" looking item and what appears to be a resonator. And I can't get ahold of the previous owner.
 

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Discussion Starter #11
On a second look at my cat it might be the same size. Can you replace those cats? And could there be an upgrade from that but in the same size?
 

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Most cat converters are made by NGK out here in Moorseville, NC. I am sure you can weld a new one on, but it wont look pretty without a good welder :)

The previous owner may have installed a ''test pipe'' which is stupid to begin with, you want a cat to pass 50 state emissions for street driven. People myth too much on that cat converters rob HP, which is not true with newer 3 way cats. The only time you don't need a cat is if its for off road racing and your engine is tuned (bigger ports, cammed, fuel system upgrade, higher cylinder compression, and standalone PCM). Drag cars don't use cats cause they run open headers that are specifically designed to dump out properly outside the collector.
 
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