# P0420 Catalyst System Efficiency Below Threshold Bank 1



## 2006altima (Sep 30, 2009)

```
http://helpforcars.net/obd_codes/p0420_nissan.html
```
I have this code on my 06 Altima. I was told at local shop that its no big deal just to run it. Machanic told me If I took it to the dealer they would tell me I had to replace the catylic converter which is part of the manifold or something and it would be like $1,000 just for the part. 

Do any of you have any experience with this and have a answer for a fix or any suggestions? Thanks a million!!!


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## 2006altima (Sep 30, 2009)

Well I replace the plugs as they needed it really bad 179,000 miles on them. I showed that this could throw catalyst code also. I reset the codes so hopefully this fixed all my problems. Thanks!


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## TubaDawg21 (Oct 23, 2012)

So did replacing the spark plugs fix it?


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## 2006altima (Sep 30, 2009)

No unfortunately it didn't. The light still goes off and on at times.


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## smj999smj (Jan 1, 2006)

Is this an I-4 or a V6?


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## 2006altima (Sep 30, 2009)

2.5 4 cylinder


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## TubaDawg21 (Oct 23, 2012)

I had this same p0420 code. My horse power went down. My gas mileage decreased. My engine would cut off and on.

I changed the front O2 sensor. After replacing the O2 sensor, this went back to normal. So I assume the oxygen sensor did need to change.

Then my SES light was still on. This time I got a different code (forgot which one it was), so I replaced the crankshaft sensor, which is what the code suggested. 

Nothing has changed after the replacement of the crankshaft sensor (other than a lighter wallet). 

Yesterday I added SeaFoam to the gas(5/8 of can) and oil (3/8 of can). I drove the car roughly 50 miles. Then I changed the oil last night.

So far after driving roughly another 50 miles, it is driving like normal and gas mileage seems to be right. And most importantly NO SES LIGHT.

So maybe I just got some bad gas and now I am good. Maybe none of this is helping. But I thought I would share with you what I have done. And as of now, I don't have an SES light.


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## 2006altima (Sep 30, 2009)

Nothing out of the ordinary with this car just the SES light is all. I was under the impression not to ever add any additives to engine or gas in my 2006 Altima.


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## smj999smj (Jan 1, 2006)

The exhaust manifold/catalytic converter assy. MSRP's for $547.33...not $1000. You can get it for $413+shipping from 1st AAA Nissan Parts Store. Rockauto.com has Dorman manifold/converters for $294 (Fed emissions) and $364 (CA emissions).


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## 2006altima (Sep 30, 2009)

smj999smj said:


> The exhaust manifold/catalytic converter assy. MSRP's for $547.33...not $1000. You can get it for $413+shipping from 1st AAA Nissan Parts Store. Rockauto.com has Dorman manifold/converters for $294 (Fed emissions) and $364 (CA emissions).


Thanks for the info. I'm sure the $1000 is with installation at a dealer.


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## FriendlyNismoTech (Oct 28, 2012)

2006altima said:


> Thanks for the info. I'm sure the $1000 is with installation at a dealer.


Do a fairly simple check, remove the heatshield over the manifold, it's 4 10mm bolts. Look for a yellow dusting on the manifold itself, if you find it then your catalytic converter has cracked and the catalyst is breaking up. This doesnt sound bad except I've had more than one customer with engine failure becaust they decided the catalytic converter wasnt important enough to replace. The catalyst back feeds into the combustion chamber, scores the cylinder walls and ruins the rings. I'm not sure what mechanic told you to "just drive with it" but he is not a person I'd allow to service my vehicles. Your dealership can perform an SRT on the catalytic converter to check if it's performing properly, it's a part of the older Consult II scan tool.


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## 2006altima (Sep 30, 2009)

About how much does this SRT test cost? I would rather be safe than sorry. The car now has almost 200,000 miles on it but its still like a new car. Its started using oil maybe 1qt between changes 3,000 miles changes.


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## 2006altima (Sep 30, 2009)

Ok I just called local Nissan which is 100 miles away. Service Tech told me up front is a $95 diagnosis fee which will go towards the cost of the repair if we decide for them to fix the problem. He also said around $700 for the part and he said anytime a converter is the problem looking at around $1,000 labor. Also he said the O2 should probably be replaced. This is just ridiculous how can they expect people to afford this type of thing. They want $229 to do a tranny service for Christ sake its drain and fill just like a oil change. If anyone has another solution for this please give me info cause I just cant afford this. Thanks for you guys help.


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## rogoman (Dec 16, 2004)

Before condemning the CAT, check on these other possible causes:

- Exhaust pipe leaks
- Intake air leaks
- Fuel injector(s)
- Fuel injector leaks
- Spark plug(s)
- Improper ignition timing


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## 2006altima (Sep 30, 2009)

Ok Thanks. I will show this to my mechanic. I really honestly don't know much about it. I figure it might be the cat with almost 200,000 on it. But maybe not.


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## FriendlyNismoTech (Oct 28, 2012)

I think you misunderstood the advisor. The total cost should be around $1000 for parts and labor. Non techs cant access techline, but if you were to call they would tell you even though the service manual indicates everything else that post aboves says are possibilities, it will be 99%of the time the converter. I had an Armada today that had a 420 and 430 code. When I disassembled the system I found that Bank 2 converter and post o2 converter were completely empty, the majorit of bank 1 converter had blown out and was clogged in the post o2 converter. I spent an hour cleaning out the muffler to get all of the honeycomb out. However, if you want to have the other stuff verified have someone hook it up and monitor the A/F Alphas, and the ST/LT fuel trims. If these numbers are normal then you can bet on your converter being shot. 

If you want to check something yourself, pull the heatshield off the manifold, this is also the converter for your vehicle. Inspected for yellow dust, and listen for exhaust blow. The QR25 is known for cracking them where the manifold welds to the converter on the backside near the block. I replace at least 2 a month under the 8/80k emissions warranty.


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## 2006altima (Sep 30, 2009)

Ok Thanks for the info. Greatly appreciated.


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## 2006altima (Sep 30, 2009)

*Part to Fix*


```
http://www.trademotion.com/parts/2006/NISSAN/ALTIMA/S/?siteid=214143&vehicleid=1432235&section=EXHAUST%20SYSTEM
```
So is this the part needed to replace the Converter/Manifold? The second one down Federal Emissions? I live in Arkansas and will never go to California. Plus the #2 gasket I would assume. And a front pipe seal?

Wow for these 3 parts shipped its $636.42 plus have to pay labor for someone to do it. It may be just as good to go to the dealer and pay the $1000 for parts and labor.

RockAuto seems alot cheaper but unsure of exact parts I need there.


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## 2006altima (Sep 30, 2009)

I emailed Rock Auto and this is what they sent back. Will someone please verify that this is correct? I will order if its my problem. Suppose to be going to my mechanic tonight to diagnose. Thanks.


```
http://www.rockauto.com/catalog/raframecatalog.php?cartid=44d02e4670f46da89d7d359f1d87b0a7
```
Click Shopping Cart Tab in top right corner to view items.


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## 2006altima (Sep 30, 2009)

Turns out gonna be going tomorrow evening to see the Mechanic.


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## FriendlyNismoTech (Oct 28, 2012)

You need 1,2, & 7. The manifold, and upper and lower gasket. The lower is actually called a bearing. Going to California has nothing to do with California emission. Vehicles sold in California have a different set of emissions they much abide by. So those cars have different exhaust systems.


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## 2006altima (Sep 30, 2009)

FriendlyNismoTech said:


> You need 1,2, & 7. The manifold, and upper and lower gasket. The lower is actually called a bearing. Going to California has nothing to do with California emission. Vehicles sold in California have a different set of emissions they much abide by. So those cars have different exhaust systems.


Ok but what about the link in post #19 the rock auto parts? Click on that then go over to shopping cart tab and the parts are in the cart. Will you look at them and check to see if there right? Its what rock auto sent me back that I need. Its much cheaper than the OEM Nissan site. Thanks again.


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## FriendlyNismoTech (Oct 28, 2012)

Yes those are the right parts, don't worry about the heat shield bolts. They're standard M6x1.00, Just get them in 1" with a lock washer and washer.


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## 2006altima (Sep 30, 2009)

*Thank you very much for your help and info.*


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## FriendlyNismoTech (Oct 28, 2012)

You're very welcome, there is a support bracket on the bottom of the cat that bolts to the block. Likely yours is broke. Have it repaired if you can or get a new one. If you leave it off you can actually damage the cat through torque rotation. Have a happy thanksgiving.


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## 2006altima (Sep 30, 2009)

```
http://www.ebay.com/itm/300818027868?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
```
Hey I hate to bug you again but I found this on ebay and was wondering if it would be ok to use it? Comes with Manifold/Converter and all gaskets and hardware to install. Please read it and let me know. Almost cant resist for $249 shiped to my front door. Thanks again!!


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## FriendlyNismoTech (Oct 28, 2012)

2006altima said:


> ```
> http://www.ebay.com/itm/300818027868?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
> ```
> Hey I hate to bug you again but I found this on ebay and was wondering if it would be ok to use it? Comes with Manifold/Converter and all gaskets and hardware to install. Please read it and let me know. Almost cant resist for $249 shiped to my front door. Thanks again!!


Yes that will work as long as you're positive you don't have a California emissions car.


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## 2006altima (Sep 30, 2009)

How to I find this out about the California emissions?


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## FriendlyNismoTech (Oct 28, 2012)

Easiest way I can think of is to look underneath and see if it has a 3rd O2 sensor after the secondary cat.


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## 2006altima (Sep 30, 2009)

Ok I can do that. I dont think it does. When we were having problems a few months ago we got the crankshaft and oxygen sensor replaced. I was only aware it had one oxygen sensor.


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## FriendlyNismoTech (Oct 28, 2012)

Well you'll have an upstream O2 sensor and a down stream. On a California car there will also be a third one after the secondary cat. You can see on the link you provided there it has 2 holes for sensors. The third will be mid car in the center pipe.


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## 2006altima (Sep 30, 2009)

I looked under the hood for Emissions sticker for California or Federal but my luck no stickers anymore. You can see where they was but gone now. I do have the window sticker of the car when we got it new and it says catalytc converter 50 state emissions control system on it but dont know what that means.


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## 2006altima (Sep 30, 2009)

FriendlyNismoTech said:


> Well you'll have an upstream O2 sensor and a down stream. On a California car there will also be a third one after the secondary cat. You can see on the link you provided there it has 2 holes for sensors. The third will be mid car in the center pipe.


I will check for the 3rd sensor tomorrow. Way to cold and dark out right now. Thank you again for your info. This is a learning experience for me.


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## FriendlyNismoTech (Oct 28, 2012)

You could really do the install yourself with some basic hand tools as long as you don't live in a northern salt state where it's all rust. I have a 2002 apart down to the crank/pistons right now in one of my bays. It had a bad converter, luckily though it blew out the bottom not the top. Head gasket just happened to go too. Vehicle has 241k miles on it and the timing components still look good. Good thing though as the lady wont pay to have them replaced while I have the hole thing tore apart.


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## 2006altima (Sep 30, 2009)

Yea I think your right about doing it myself. Having trouble finding a California emissions one to buy right now without paying a arm and a leg. Thats all I can find on eBay is non California. That Rock Auto link I ask you about I'm pretty sure it was non California also. I live in Arkansas.


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## FriendlyNismoTech (Oct 28, 2012)

I will get you a list of needed tools tomorrow when I put this one back together. Just had a brainstorm, give me your VIN and I can run it on my NNANET and tell you if it's Cali.


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## 2006altima (Sep 30, 2009)

FriendlyNismoTech said:


> I will get you a list of needed tools tomorrow when I put this one back together. Just had a brainstorm, give me your VIN and I can run it on my NNANET and tell you if it's Cali.


Ok. I will send you the Vin# via PM.


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## 2006altima (Sep 30, 2009)

Well I don't see a 3rd O2 sensor nor do I see a second one on bottom of the Manifold cat. As best as I can tell there is only 1 sensor up at top of first converter easily accessed by just by raising the hood. All the cats I see to order OEM or not has a O2 location before and after the Cat that's connected to the manifold. So what if it only has one? What is the second spot for on the lower end of the Manifold/Converter?


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## FriendlyNismoTech (Oct 28, 2012)

I promise you there is a second after the cat. Likely a heat shield is inhibiting your view. The first one reads the oxygen content when the exhaust leaves the combustion chamber, the one after the cat reads it again to make sure the cat is functioning properly. It has to have at least 2 per bank. You'll need a 14mm, 12mm, and 10mm for the job. I suggest 1/2" drive deep well with a 3" extension to remove the manifold bolts. The Alternator has to come off before that manifold will. It's held in by 2 14mm bolts. One is very long and you'll need to remove the Coolant overflow, and IPDM "fuse box" to get it out completely. The heat shield is all 10mm bolts, don't worry if they break you can replace them with M6x1.00 bolts 1/2" long. The new manifold will likely not line up perfect with the heat shield, even factory ones don't. Unhook the battery, you need to unhook the alternator and if you arc the main lead off of it you'll ground out the circuit and make a light show. If you need anything else lmk.


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## 2006altima (Sep 30, 2009)

Cool man. Thanks again for all the info. My X bro in law is a mechanic at a local automotive shop. They have a nice scan tool and all the proper tools to do it with and hes gonna help me do it. I appreciate you taking all the time to help me out. I found that converter I showed you off ebay on the people main website and its cheaper on there I guess cause of no ebay fees. Check it out its $229 free shipping. Thanks again!!!

```
http://www.bestandfox.com/2006_Nissan_Altima_2_5_Catalytic_Converter_p/60-1340.06.htm?gclid=CPWN8MSC87MCFQyDnQodfBkAPg
```


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## FriendlyNismoTech (Oct 28, 2012)

That's crazy cheap. Congrats, and good luck. Let me know how it turns out.


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## 2006altima (Sep 30, 2009)

Ok I will. Gonna talk to my bro and maybe get this ordered tonight. Be next week before I can tackle it. I gotta work fri,sat,sun 12hr shifts. Thanks!!


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## 2006altima (Sep 30, 2009)

Well I got it done total project cost $229. My X bro in law helped me and didn't charge me a dime. Took a 1hr 1/2 from time we raised the hood till we shut it. All went well all bolts come out easy and everything went back in and lined up without any hassles. The bolt at bottom of converter that screws in side of the tranny housing or block was busted off. The bracket itself wasn't broke the case hole that the bolt screws into was busted off. I'm gonna include pics so you can see. I'm gonna see if someone can weld this back on so it will be secure at the bottom cause I know it needs to be. The code cleared itself a few seconds after we started the car. All is good now except the bottom bracket. I thank you again for your help. This saved me a ton of money.


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## 2006altima (Sep 30, 2009)

Anyone know a way to fix the mount thats broke off for the bottom of the converter? Its btoke off the housing.


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## SPEEDO (Jun 9, 2003)

if you still have your old cat, there are people that will buy them for cores..


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## 2006altima (Sep 30, 2009)

Yea I got it. Do they buy them at the recycle places or muffler shops?


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## hotrodwillys (Aug 3, 2015)

I have a V6 SE Altima from 2003. It has 217,000 miles on it. Before replacing the Cat verify its operation. Given the operating nature of the CATs the output (or downstream) should be hotter than the front (inlet) temperature measured at each flange. If its not then the CAT is likely bad. Given how tight it is on the V6 SE, I just took the chance and replaced the downstream Oxygen sensor located at Bank 1 (the 3 cylinder bank closest to the firewall) - after backprobing it and noticing the fast fluctuations of the sensor's operation. Get the BOSCH Oxygen sensor with the proper connector attached (the BLUE colored) connector was the proper one in my case. It cleared the P0420 code and has been off for over 400 miles now.


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## Altima! (Jan 13, 2016)

He guys I also have the P0420 service engine light on issue. According to Autozone this is what it read:

Catalytic system efficiency below threshold - bank 1 probable cause.

aa - Large vacuum leak - changed the PCV valve (no change) - any ideas?

aa - Fuel system fault - probably the cheap gas I've been using - I used Mobil & Chevron in the past (premium wht or blue) to turn the SEL light off. 

aa - Ignition system fault - may the used battery I'm using! - I've noticed the car I bit slow to start however, it does start.

aa - Failed bank 1 catalytic converter. - informed to change spark plugs ( issue remains), after reading previous post submitted I am going to change the O2 sensor upstream and see if that does it. I will updat the post once I have that taken care of. short on funds so it may be a while before the thread is updated. thx in advance


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## quadraria10 (Jul 6, 2010)

Hi 2006Altima
Curious if you still have your altima, and how your new pre-cat is holding up? They look to be a very good deal and pretty good quality.


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