So for about a month now i had this p0401 code ... i took it to a mechanic and he suggested to me that i need a new cat ,didn't specifically state which one .... & how could i be able to tell which one is clogged he did say i needed to replace my exhaust manifold b/c it was in very bad condition due to it sitting in snow prior to buying it last yr. ... is this mechanic bsing me or could he be telling the truth b/c he did explain one of my tail pipes has exhaust coming out and the other doesnt....i also did see the manifold and Front cat from looking in ,under the hood and seen it was in bad condition..

i just don't wana drop that amount of money buying a front & or rear cat as well as an exhaust manifold....

Also is it a bad idea to go aftermarket for the exhaust manifold or cats? ?

Which would be best brands ??

 

Are you sure the code was P0401? It is not in any 4th, 5th or 6th gen service manual. There are P0400 & P0403 codes that are EGR related.

The codes for the bank 1 & bank 2 pre-cats are P0420 & P0430 respectively.

 

positive it wasnt the bank 1or 2 cde & when i lookit up it says exhaust gas recirculation insufficient on nissanhelp.com

 

OK, so this is another unlisted code, just like the P16xx codes for NATS.

I don't think your mechanic was correct to say that you need to replace the cats. But since Nissan eliminated the EGR valve in 2001, I am not sure how to go about fixing the problem.