The Nissan Club banner
1 - 20 of 27 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter · #1 · (Edited)
Hello,

I am working on my niece's 2005 Nissan Altima S 2.5L . She is currently getting codes P0420 and P1273. She already had the front and rear O2 sensors changed and still getting these codes. The last piece changed was the rear O2 sensor. The codes were cleared. The SES light stayed off for a couple days and came back on with codes P0420 and P1273.

I have read many, many posts about code P0420. I would like some confirmation on what I think I understand from these posts.


Let me explain what I take from the posts on code P0420-
  • P0420 relates to the pre-cat located in the exhaust manifold
  • These pre-cats are notorious for failing
  • Failing pre-cats located so close to the engine run a grave risk of having the engine suck in debris from the pre-cat causing premature engine failure, poor mileage, exhaust plugging
  • The only way to check the condition of the pre-cat is to take it off the car and visually check.
  • As long as the pre-cat is on the car I run the risk of pre-cat failure
  • The only long term fix it to eliminate the pre-cat and replace with a header with no pre-cat
  • If the header is installed and there is no pre-cat the air reaching the rear O2 sensor is not as "clean" and will trip the rear O2 sensor
  • The fix for tripping the rear O2 sensor is the O2 sensor spacer
  • Technically, we may be able to eliminate the tripping of the rear O2 sensor by only installing the O2 sensor spacer, but still risk the hazards of a bad pre-cat and premature engine damage

Can someone tell me if I am on the right track? I want to confirm before buying the parts.

Thanks in advance :dunno:
 

·
09 Altima 3.5SE 6MT Sedan
Joined
·
6,365 Posts
Yep, you've clearly done your homework...congrats and thankyou.

The only thing I would add is that I would pull the precat first before ordering any parts. If the cat is deteriorated, then rather than buying new precats, I'd jump straight to buying a new JDM engine (which comes with perfectly good precats). Not going to be that much more $ overall once you factor in labour...but you avoid the whole 'my engine was damaged by catalytic matrix dust, is terminal but I am still in denial, and I just foolishly spent well over a grand on it' misery.

The only other indicator is oil consumption, which by the time you notice...you can jump straight to the new engine and skip checking the precat.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #4 ·
If the cat is deteriorated, then rather than buying new precats, I'd jump straight to buying a new JDM engine (which comes with perfectly good precats). Not going to be that much more $ overall once you factor in labour...
A whole engine? Confused :confused2 What I had read was I could replace the exhaust manifold / precat with a header. The header was about $110 on Amazon. The O2 spacer is cheap. Surely as long as the engine is running OK, no/low oil consumption this would be the cheaper and correct route. Do you agree?
 

·
09 Altima 3.5SE 6MT Sedan
Joined
·
6,365 Posts
Hey, it's your car your choice.

My thinking is that ceramic powder, once introduced into the engine...tends to stick..literally...around for quite some time. This has the effect of mixing a tube of toothpaste into your engine oil...not immediate, not catastrophic, but over time parts will wear much quicker than they should. Think of it as radiation poisoning, you can take a lethal dose and walk away without knowing it, but a couple of days later, blisters, rashes, organ failures, death. So, if there's a chance an appreciable amount of dust has been sucked in, or it's been happening for some time, my recommendation is a good used engine...a la JDM...run you $500-$1000 and includes everything, cats, AC compressor, alternator, everything...and typically with <35Kmi on it.

Why take a chance on a 'lethal dose' engine...when you can effectively start over for another $500 say.
 

·
09 Altima 3.5SE 6MT Sedan
Joined
·
6,365 Posts
double post
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #7 ·
OK. I am asking my niece (via email) if she is using oil. My plan is to recommend the new pre-cat or header if she is not using oil yet. If she is using oil I would recommend she consider one of those engines. They are a good deal.


Reading and digesting all the posts on this subject was difficult at times to put all the pieces together. Thanks for helping me figure it all out.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #8 ·
OK. I am asking my niece (via email) if she is using oil. My plan is to recommend the new pre-cat or header if she is not using oil yet. If she is using oil I would recommend she consider one of those engines. They are a good deal.


Reading and digesting all the posts on this subject was difficult at times to put all the pieces together. Thanks for helping me figure it all out. :wink
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #9 ·
One more thing.

My niece told me last night the care is not using oil. So the car is running fine, minus the light on the dashboard. She doesn't have a ton of money, so I was not surprised she decided to go the route of the header and rear O2 sensor spacer.

On the rear O2 sensor spacer on these 2005 Altimas- Do I need to get the one with a 90 degree bend or is there enough clearance for a straight one?
 

·
Registered User
Joined
·
600 Posts
P0420 , o2 spacer , header mod!

One more thing.

My niece told me last night the care is not using oil. So the car is running fine, minus the light on the dashboard. She doesn't have a ton of money, so I was not surprised she decided to go the route of the header and rear O2 sensor spacer.

On the rear O2 sensor spacer on these 2005 Altimas- Do I need to get the one with a 90 degree bend or is there enough clearance for a straight one?
Good to hear not burning through oil , that's good!

Basic straight style spacer does the trick , fits fine in the midpipe o2 bung, she will be set when matched with a header. I have some options!

Thank you,

Mark
 

·
Registered
Joined
·
443 Posts
A whole engine? Confused :confused2 What I had read was I could replace the exhaust manifold / precat with a header. The header was about $110 on Amazon. The O2 spacer is cheap. Surely as long as the engine is running OK, no/low oil consumption this would be the cheaper and correct route. Do you agree?
Yes, as long as the engine is in good general condition and not burning oil, replacing the stock exhaust manifold with a header is a good route to take. Many folks have done this with good results. The O2 spacer is needed to fool the ECU.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #12 ·
The parts are ordered. Thanks for the confirmation, Rogoman.
 

·
never take it to the shop
Joined
·
1,621 Posts
So there is no oem replacement cat that will not destroy your engine? I haven't had any issues with the rockauto cat. I am in virginia no way in the world I am going to put on a header now they have mobile emissions so even if you pass 3 mos ago they can get you at any time.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #14 ·
Folks- May need a little more help. Installed the header and rear O2 sensor spacer. Notable performance improvement. We cleared the codes, but the light came on again. Only one code this time; P1273.

Any tips for this one?
 

·
Registered
Joined
·
443 Posts
Folks- May need a little more help. Installed the header and rear O2 sensor spacer. Notable performance improvement. We cleared the codes, but the light came on again. Only one code this time; P1273.

Any tips for this one?
At this point, you might want to check the following:

● Fuel pressure may be incorrect. Tee in a fuel pressure gauge at the inlet to the fuel rail. The spec at idle is: 51 psi
● Intake system vacuum leaks. To check the intake system for a vacuum leak, attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #16 ·
The P1273 code was present before doing the header and O2 sensor spacer. So although the P0420 is gone this remains. Could there be any correlation between the work I did installing the header and this code? Kinda doubt it, but one site mentioned it could be related to an exhaust manifold leak.

Anywho- I can setup to check the items you have mentioned. Thank you.

Could you please explain what code P1273 is related to (in layman's terms)?
 

·
09 Altima 3.5SE 6MT Sedan
Joined
·
6,365 Posts
So, at least on my VQ, there are two O2 sensors...the first is the air/fuel sensor aka upstream (which is causing the P1273) and the second or downstream is monitoring the cat efficiency. You only put spacers on the downstream sensor...if you put them on the upstream, or damaged it during the work, then you'll throw P1273's (which is the ECU's way of saying, 'Hey, I'm messing with the air fuel ratios based on the MAF sensor inputs, but my exhaust ratios aren't changing like I'd expect') In short, it doesn't believe the reading coming back from the upstream AF O2 sensor.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #18 ·
The computer does not believe the reading coming back from the upstream O2 sensor. It had been replaced (not by me) a month or so before installing the header. I was careful with it in transferring it to the header. I never thought about installing a spacer on that one. Only the downstream sensor. So, I could have a bad upstream O2 sensor or issues with the other items you mentioned. I will try to isolate.
 

·
09 Altima 3.5SE 6MT Sedan
Joined
·
6,365 Posts
Also check to make sure the correct part number was installed. Upstream and downstream have different part numbers as well, so are not interchangeable.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #20 ·
I am not sure how they could have installed the wrong part number upstream vs downstream. They each have a different type of electrical connection.
 
1 - 20 of 27 Posts
Top