# P0420 code on 08 Frontier 6 cylinder (Nismo)



## okieactor (Nov 6, 2017)

I have got a P0420 code on my Nissan and am afraid that with everything else that's been a problem with it, if I can't get it fixed, it may be time for a new truck. See details below. I'm looking for what process to go through to get it taken care of.

HISTORY
In the summer I had an error code for an occasional misfire on cylinder 1. I replaced all spark plugs and coil-on-plug for cyl1. It stopped that error code, but then the P0420 came up. I'm due for inspection this month and it's going to fail due to the check engine light on.
Around 160k miles

P0420
-Says that bank 1 catalytic system efficiency is below standard.
-Seems to generally be either O2 sensor or catalytic converter.
-I have no way to tell which it might be without replacing parts until I find it.

OTHER STUFF WRONG WITH IT
Cracked windshield (still passed previous inspection with that since it's not bad enough to affect the wipers)
Needs new shocks/struts all the way around, I think.
Has new brake pads from last year. Brakes are good.

DONE ALREADY
-Ran Seafoam through it, no change.
-Watched a bunch of youtube videos on P0420.

CONSIDERING DOING THE FOLLOWING:
-Going to Nissan Dealer to see if they can do any deeper diagnostic to prevent fixing the wrong parts.
-Running Cataclean for $25 (pretty much decided I will at least try this for the cost)
-Replacing O2 censors on bank 1 (right side??) myself.
-After that, deciding whether to replace catalytic converters. (Scary, since I think there may be 4 O2 sensors, and front/back cats??)

CONCERNS
-Money, obviously. 
-Chasing the problem around trying to fix it myself. Which is only slightly better than having a mechanic chase it around for a higher fee, if they don't locate it correctly at first either.

ANY HELP IS GREATLY APPRECIATED. Thank you, sorry for all the details. New member here.


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## smj999smj (Jan 1, 2006)

Often when you get a misfire on these vehicles, it doesn't take long to ruin the upstream converter. Bank #1 is the right side of the vehicle, same as your misfire side. While it's true that a faulty air/fuel ratio sensor (upstream oxygen sensor) or rear oxygen sensor can cause a catalyst code, most of the time they will also trigger a code, as well. Catalytic converter failure is not uncommon on Nissan vehicles with the VQ40DE. Both upstream converters have been replaced on my 06 Pathy; the left went at 84,000 miles and the right went at 150,000 miles (and now I'm getting a code for the left, intermittently, at 180,000 miles). My 08 Pathy, on the other hand, has 210,000 miles and all of its original converters and sensors! So, there's no rhyme or reason to it, it seems. If you don't have any other codes than the catalyst code and there are no exhaust leaks or running issues with the engine, then you likely need a new, upstream catalytic converter on the right-side bank. Most techs will usually recommend replacing the upstream air/fuel ratio senso (use NTK or Denso brand) on that bank if you do replace the converter. I go with Walker catalytic converters for replacement, but if you live in an area that has C.A.R.B. emission requirements, especially California, you may not have many options other than a genuine Nissan replacement part. Walker does make C.A.R.B. certified converters, but I'm not sure if the one they make for this vehicle is or not. You don't have to worry about the rear converters 99% of the time as they are not monitored by the ECM. The only reason they would need to be replaced is if they were leaking and couldn't be repaired, damaged or if the substrate inside the converter was rattling or clogged. You also need only replace the side that is triggering the code.


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## okieactor (Nov 6, 2017)

A friend has suggested taking it to a Nissan dealer and seeing if they can run a more advanced diagnostic than the Autozone/O'Reilly people can run. Is this a thing? 

If it is indeed a catalytic converter, it's going to be expensive, and so I'd want to be as sure as possible.


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## smj999smj (Jan 1, 2006)

Only thing a Nissan dealer will do...which is no different than what any competent independent shop can do...is install a scan tool and monitor the air/fuel ratio sensor signals to see if they are in range and monitor the rear oxygen sensor signals to see how they are acting. They don't have a magic machine that they can hook up that will say with any certainty that the converters are bad. Air/fuel ratio sensors operate in a much narrower range than oxygen sensors and the best way to tell if they are not operating properly is when they trigger a code. You can get a Walker right-bank, upstream catalytic converter for $168+shipping from Rockauto (plus you'll need a couple of gaskets) and an upstream, Denso sensor for $60. A Nissan dealer will likely charge you $100 just for the diagnosis and probably quote around $1000 for the same parts and not including labor, hazardous material charge and tax.


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## okieactor (Nov 6, 2017)

Thank you for your help. Will the rock auto cat require welding, or is it bolt-on?


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## netxtown (Jun 24, 2016)

I have a 2005 fronty and replaced both cats at 180k (both were throwing codes). I bought Pacesetters and so far they are fine. My nephew had access to a shop...so i got to sit back and observe as he and his buddy did the work.

#1 Heat shield on driver's side was PIA since the studs snapped off on the manifolds.
#2 Loosen the back of the whole shebang so that when the cats are unbolted from the exhaust manifolds the entire exhaust will slide back and make life much easier.
#3 Install new gaskets. repeat!!! Install NEW gaskets. again: Install NEW gaskets!

I had the same codes (P420/430). I replaced the upper O2's to no avail. I made no changes to anything else. Once new cats were on, I reset the computer with the stomp-stomp-stomp routine, and it was done. It's been about 4 years since and no problems so far.


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## okieactor (Nov 6, 2017)

Netxtown: Are you also saying front cats is what you replaced?


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## smj999smj (Jan 1, 2006)

okieactor said:


> Thank you for your help. Will the rock auto cat require welding, or is it bolt-on?


They are direct-fit replacements. No welding is required.


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## okieactor (Nov 6, 2017)

I ordered the walker front right cat through rock auto (and 2 gaskets). I'm nervous, but hope I can get it done over break next week.


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## smj999smj (Jan 1, 2006)

With the plastic wheel well liner, two of the nuts/bolts that attach the converter to the exhaust manifold are pretty easy to access once the heat shield is out of your way. The one on the bottom is best accessed from underneath the vehicle.


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## okieactor (Nov 6, 2017)

Is a Hanes manual still a hood resource or is there something more modern that's better? Or anyone aware of a step-by-step for the feont cats online?


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## smj999smj (Jan 1, 2006)

I always use the factory service manual. There isn't anything better as far as the amount of information. You can download them for free at various place on the web, including Nico Club's website.


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## netxtown (Jun 24, 2016)

Yes - I replaced both of the front cats. 
I read on down the thread - and it sounds like you are only going to replace one side - but getting two gaskets (danged good idea!).

You will fight the exhaust system until you turn blue if you don't release both sides at the same time. Unbolt the pipes from the cats - and i believe there is one hanger you can loosen at the back mid-center. Doing so allows you to slide the whole exhaust assembly to the rear and gives you few inches to remove the cat. Then, using a ratcheting type strap, you can easily pull the assembly forward a little at a time. Slip in your gasket, then ratchet to align the bolt holes...then take it up tight.

NOTE: My nephew and his buddy fought the exhaust assembly for at least a couple hours. Of course, when I wasn't looking, they just left the old gaskets in and bolted it all back up. Within a week it threw a code, and i took it to a 'real' shop. They put it up on the rack and found the leaky gaskets. I watched how he unbolted and then put it back together. I know with a rack it makes it much easier - but sliding the exhaust assembly towards the rear was key to it being done in less than an hour - and 15 of that was cool down time for the cats.

Oh, for what it is worth. Nissan wanted $2300 to replace both cats. After I paid the Emergency Room bill - I decided to bring it home....


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## okieactor (Nov 6, 2017)

Update: I'm in progress now. I decided to use 2 days so I wouldn't get tired and stressed out. I think I'm about 90% done getting the old one out. Here are details.

Supported truck via jackstands on the side part of the frame where it seemed to seat really nice and another one under a major crossbar of the frame under the engine area. Jack is in place as a backup as well, but isn't really absorbing any weight, and I removed it for overnight tonight. 

Used silicone spray on all the bolts I knew would be part of the project the day before. I may have forgotten one of the bolts on the rear cat since I was not removing that one. (But see delay below.)

Removing the plastic wheel-well cover: No problems there. Using a plastic storage bin to catch all parts taken off.

Removing O2 Sensor: Got a loaner part at AZ, no problem there, that took under 3 minutes once I had the tool. The standard O2 adapter fits, no logistical issues there, did not need the one with crowfeet.

Breaking loose the bolts on the cat: Difficult, but if lubricated in advance, it is doable.

FIRST PROBLEM: There is a tin or aluminum housing that seems to shield the exhaust manifold from the wheel well. You have to get this out of the way to access 2 of the bolts on the front cat. It has 3 small bolts (which it turns out screw directly into the exhaust manifold). I guess because these probably get REALLY hot, and because they didn't choose a good size or heavy-duty type of bolt, these are prone to breakage. Even with using silicone spray, 2 of 3 broke off (never even strained, they just gave way all of a sudden). One of 3 fell down into a part of the suspension arm or something. So far I can't find it. So I'm just moving forward, but there are at least 2 issues that will need addressed later on. Not sure how big of a deal they are yet.

Getting the front Cat out. After watching a youtube on this, I am loosening the back cat as a means of creating enough sloppiness in the linkage to get it to clear. That's for tomorrow, as one of the bolts on the rear cat is really stuck (think I forgot that one last night when I lubed all the bolts). I anticipate that once I break loose both bolts on the back cat, it should be easier going. Then deal with installing the new one, figure out what to do about the missing bolt and housing (can it be held on by just one bolt and be okay??), etc. Will send further updates as I know more.


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## netxtown (Jun 24, 2016)

Okie - The bolts on the heat shield on my driver's side all snapped. Oh well...no more heat shield. I just left off.

My rear cats are welded on....but they slid the entire assembly - to the rear about 2-3 inches. This gave enough room to bolt the front cats to the manifolds easily. Then they used a ratcheting strap around the muffler and the center cross beam to move the exhaust assembly forward. Slipped in the gaskets, pulled it up tight, and was done. I know that is 'easier said than done' - but I was amazed at how easily the whole thing just slid right back into place.


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## okieactor (Nov 6, 2017)

So, I could not make the whole assembly slide back, because I'm not doing both cats. I attempted to released the back right cat, that proved problematic. I think shops with pneumatics, or just the age of the bolts, etc., has made it tough to break free a bunch of parts without stripping. So I couldn't even get the back cat loose on one of the bolts. 

So I tightened it back up and instead undid all the exhaust anchors on the right side all the way back to the tailpipe. This creates a pinch sort of situation where you have to support somewhere under the muffler, or the downward pressure makes it impossible to get the cat out. Did that and still struggled, just couldn't bend the exhaust system enough to get that clearance. Finally understood the use of the truck strap, though, at least in my position. I hooked it from the crossbeam at the tailgate to the front of the muffler and tightened until that gave me clearance to get the cat out. 

Other Small Issues:
--Walker replacement from Rock Auto came with open holes at the downstream side, not welded bolts like the original. So I had to go to AZ on that.
--With tension on the muffler I'm struggling to get the cat threaded enough from both ways so that when I release the truck strap (fingers crossed), it will hopefully just pop back in.

Will send updates when done.


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## okieactor (Nov 6, 2017)

And...done. Will give updates once I drive it 50 miles and hopefully get it inspected.

2nd Thoughts:
--Wish I hadn't broken those 2 bolts off that held the heat shield onto the manifold. I wound up putting the one existing screw back and that's holding the shield in place.
--The auto shop that my wife wanted me to use said that aftermarket cats fail after 6 months, so that is also ringing in my ears. Hope that to be false.

Tricks/Suggestions
--Use a truck strap to pull the muffler back (loosen all exhaust anchors first).
--Use C-clamps to close those gaps back up enough to get bolts threaded before releasing the truck strap.
--Very careful on the bolts to the heat shield that covered the front cat and side of the manifold from the wheel well area. They break VERY easily.
--Stay patient.
--Loosen the exhaust system and use the truck strap first. Don't even mess with trying to loosen the back cat. 
--Random helpful tools: Dentist mirror, extendable magnet, c-clamps, truck straps, combo wrenches and deep and shallow pan sockets, hammer as needed, phillips screwdriver, bucket for spare parts, lots of silicone spray lubricant or the like, headlamp AND a clip light of some kind, O2 wrench socket from Autozone loan-a-tool, your lug wrench and special lug bolt adapter, jack, 2 jack stands, use wheel as a 3rd backup under the brake disk/also a place to sit while you work in the wheel well.


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## netxtown (Jun 24, 2016)

I'm not sure why these auto shops all have the same mantra about aftermarket cats. Mine were warranted for 2 years...and no problems so far after 3 years in place.

Glad you got it all done and you are back on the road again!


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## smj999smj (Jan 1, 2006)

I have at least 2-years on the Walker converter on my 06 Pathy and haven't had any issues yet. The key is to stick with a good brand. I have seen some people have problems with Magnaflow converters years back, but I'm not sure if they've rectified those problems in their current converters. I would avoid the generic converters available on Ebay, however.


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