Guys,

Please have a little patience with me. I want to learn how this works. I've gone through plenty of search results but the technical stuff is a little bit above my level. I've had a recurring P0420 code. After talking with Dave B at Southpoint Nissan, he seemed to think my next course of action would be to replace the main cat. But I'm confused since the diagram below doesn't show a main cat. Where exactly is the main cat located on this diagram? Dave suggested that I needed to replace the Y-pipe. How is the Y-pipe related to the cat? Can someone take the time to clarify this for me. Thanks.

 

the "main cat" is labeled "rear cat" on that picture.

the y-pipe has precats. the main cat has to heat up to work. the precats do the job until the main cats heats up.

an aftermarket y-pipe will replace everything in front of the main cat in that pic

 

partially correct, the precats heat the exhaust gasses so that the main cat can do it's job more efficiently...But yes, the main cat is the "rear cat" in the picture and precats are in the y-pipe on the VQ30.

 

arent the exhaust gases already hot?
i thought that the precats were only needed when the car is warming up. after the main cat is heated up, the precats arent needed. thats why when you have a y-pipe, you can pass inspection if the car (and main cat) is warmed up.

 

Yes, the precats allow the cat to reach operating temperature quicker, and you're right about cold start emissions, but I'm pretty sure precats continue to do their job even after the car is warmed up and the precats don't necessarily do the cat's job...

 

If I have to replace the pre-cat because of a 0430 (not 0420 - had that already and fixed with o2 sns), can I replace the entire Y pipe and not spend the cash on another pre-cat? Will I still pass inspecton (PA) where they hook the ems meter to the tail pipe? Anything else I need?

Forgive a stupid question, but when everyone talks about a bad cat related to hte 0430, is that pre-cat or rear (main) cat?

 

Man, this is confusing. I've got the 0420 code and I was under the impression that I had to replace the pre-cat. I thought 0430 was for the main cat. Exactly what O2 sensors did you replace to get rid of 0420?

 

I had the cattman y-pipe with the cattman fastcat which is the catalytic converter, and passed the inspection with no problems.

I'm in houston, texas so I don't know how strict the inspection would be in other places in other states.