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Discussion Starter #1
Hi all
My 05 Altima 2.5s 320k miles.
Flexpipe went under engine and precat had a crack somewhere where the pipes weld to the cat.
So I decided to replace the header pipe and put 2 new sensors and new flexpipe.
Everything went pretty good except now the check engine light has come on with the 420 code for catalyst efficiency.
I did the same on my 03 but put non foulers on the o2 sensors and it was perfect.
This car has some differences though. The b1s1 is not a o2 sensor, but rather a air/fuel ratio sensor and the head is too fat so it bottoms out in the non fouler before it is tight.
The B1S2 is in the pipe under the car right by the flex rather than on the header pipe like my 03.
Can someone who has done this on a 05+ successfully please tell me where you put the non fouler(s) if used and if there was any 420 code.
On the bright side this car is quiet, has nice tone, and noticeable improvement in power and shifting. Best this car has ever ran
 

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An O2 sensor and air/fuel sensor are the same thing. You don't put the non-fouler on S1, you do it to S2, the second one. Likely the exhaust crack leaked enough to cover up the 420 code and now it shows with no leaks.
 

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Discussion Starter #3 (Edited)
The 420 is caused because I deleted the precat.
So you are saying non fouler has to go in pipe under car at B1S2
So I just swapped in a non fouler on the downstream sensor. Close but it fit.
The B1S1 is a different type of sensor, In theory same concept but the head is bigger and shaped different.
Fingers crossed that the light stays out now. I go about 20 miles and it pops on.
Thank you for the response.
Have you done yours or one?
 

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Don't have to, you want delayed action on the second sensor but absolutely not on the first as it messes up your fuel calculations.
 

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I've got headers on my 05, and NO CATS at all, also no codes. [no non fouler/spacers either]

I used oem equivalent 02 sensors from Rock Auto on the front, and the old Nissan sensors at the rear.
 

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Discussion Starter #6
Well I drove it all day today.
All monitors cleared, no engine light. Yay. Thank you.
As for the other member running with no cats you got lucky. It may catch it someday.
 

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X2, I don't see how it's possible if the system uses the same comparison data method the other OEMs do. You should need some voltage moderating method on the second ones to work.
 
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