P0420

[dickiesmalls]

I have an 06 altima s 4 cylinder with a re manufactured engine and got the P0420 code. I took it to the dealership and they came back about 20 minutes later saying the catalyst, rear 02 sensor and sparks plugs needed to be replaced (all for about $2000). I decided I would order the manifold assembly online for a cheaper price and have someone else that I normally use put it on for cheaper. I am still waiting on the part but the service engine soon light went away. Is it possible that its not bad and all they did was charge me $100 bucks to read the code that I already had without doing any diagnostics? I did drive the car for a week in some higher elevations than where I normally drive it. Could the changes in elevation or altitude mess with the oxygen readings and possibly throw that code?

[MaximA32]

Welcome to NICO! In theory, I suppose a severe change in altitudes could make the car run a bit leaner than it's used to. How many miles have you driven the car since the light went off? How long has the light been off?

[dickiesmalls]

I would say about 300 to 350 miles and the light went off yesterday so it took it about 6 days before it went off.

[dickiesmalls]

And to answer your first question about 50 miles since the light went off.

[DrewH]

I'd say a lot of things are possible. How many miles are on your car?

[dickiesmalls]

It has a little over 138 thousand. I haven't had performance problems, no bad smells everything seems to be running fine.

[DrewH]

I only ask because I don't trust Nissan cats. They have a long history of doing more harm than good. Do you keep this car fairly stock or do you mod it and where you live do they do emissions?

[dickiesmalls]

No its all stock. I use it for coming to and from work with the occasional long distance trip . No we don't have any emissions standards.

[06SE-R]

I would advise and I believe what DrewH is hinting at is to get rid of the OEM cat either completely or add a high flow cat ( relatively easy) . I did on my wife's 2.5 a looooong time ago. It's nice not having to worry about it! I will say on the 02 sensor that it is a possibility. My wife and I recently went to Hawaii on vacation and we rented a 2012 jeep wrangler with a little over 8K on it . one day we went up into the mountains and the damn thing started choking itself out and the CEL came on ( we actually had to stop a few times on the way up) finally make it to our destination and got to talking to some folks and the first thing they pointed the finger at was the 02 sensors and sure enough the whole way back it did the same thing get into town a few miles and it started running fine. I would have never given it a thought truthfully but for me it was the only thing that really made sense and I suppose those who live in Hawaii have the issue figured out lol. I'm not sure where you live etc and I know that some parts of Hawaii is at some points around 12,000-13,000 feet above sea level. My point being is that it is a possibility. Another thing I would look at is if the 02 sensors were replaced when the motor was rebuilt.

[janetsman]

I have had the same issue but on my 3.5se, I replaced the bank 1 cat as well as both the upstream and downstream o2 sensors on bank 1 as well so far so good. Only problem is never drove it enough miles afterward to really check it and went to smog it and it failed. To high of emissions due to being for so long while running to rich. So if I was you pull the o2 sensors and see what they look like, if they are black or dark gray then you need to replace them as well if they are a light gray or white then running to rich. Either replace them or damage cat

[janetsman]

You've also got to remember that just because the cel isn't on that doesnt mean the problem is gone, the ecm will maintain the code until the problem is resolved by either replacing the part and clearing the code with an obd2 reader or driving the car until its gone through all 8 cycles which is generally about 100 miles.