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P0300, P0420, P0430 Codes: Bad Catalytic Converters

21758 Views 22 Replies 12 Participants Last post by  Jigsaw419
This post chronicles a major weakness in the Frontier design that I uncovered (and solved) that concerns the catalytic converter system. I have the 4.0 L, which has a primary catalytic converter and a secondary catalytic converter on each cylinder bank for a total of four converters. I will refer to these units as “cat(s).” For most cars, catalytic converters are designed to last the life of the car. From my experience, this is not true for the Frontier. Scotty Kilmer, has a low opinion of Nissan quality and has specifically identified Nissan cats as being poor quality. :frown:

In July 2018, my mileage went over 105k which triggered the need to replace the spark plugs. I chose to use Iridium NGKs rather than Platinum. After the plugs were changed out, the engine almost immediately threw bad catalytic converter codes: P0420 and P0430. The engine ran fine and it seemed nonsense that new spark plugs could damage the cats: I considered the codes to be a “false positive.” I continued to drive the truck for if the cats were truly dead, I could not do any further damage. All along, I was struggling to figure out how new plugs killed the cats. If you check the ClubFrontier forums, you will find other incidences of new spark plugs killing the cats. Very strange.

In October, my Nismo started to throw P0300 codes (random engine misfire). These were flashing which indicates a serious error. It was then the cats were examined using SCAN on the upstream and downstream O2 sensors. Yep, the cats were dead. The tech said if they were changed out, it would also stop the engine misfire P0300 code. With the forebearance of $1,500:crying:, the cats were changed out along with the two upstream O2 sensors. It is axiomatic that if one makes a large donation at the car repair altar, good things will happen. The dead cat codes, P0420 and P0430 no longer registered. The engine ran very well, idled smoothly and could rev to 6k rpm. But the random misfire code, P0300 remained. In fact, it appeared much more often and continued to flash much longer. I could no longer drive the Nismo because the misfires could send excess hydrocarbons into the exhaust, which will damage my new cats.

The tech then utilized a rigorous protocol to uncover the reason for the misfires. All ignition electronics including the new plugs were checked. Fuel pressure and volume flow were checked. The intake plenum was checked with carburetor cleaner and smoked to find small leaks. MAF and EGR were check out. All injectors were tested and cleaned as needed. Compression and valve timing were checked. Nothing worked as the truck continue to throw P0300 codes in a fast and furious pace. The tech spent a lot of hours on the truck and had nothing to show for his efforts. He personally did not think the engine was misfiring.

We were running out of options. My research in this Clubfrontier website came up with a post of another owner who also had P0300 woes. His solution was to gut the secondary cats and the problem went away. I gave this tip to my tech and he ran with it. In his tests with disconnected secondary cats (very loud!) he did not get the P0300 code. This was the smoking gun, the secondary cats were plugged!:surprise: Another benefit discovered during this test is that my engine put out significantly more power (10-20%). The secondary cats were replaced, no more codes. Problem solved. I can now drive my Nismo. Thanks to this Clubfrontier Board, I was able to alert my tech on the plugged secondary cat root cause.


How did changing of the spark plugs cause the P0420 and P0430 codes to appear? Best guess: New spark plugs will provide a better spark. How this played out in the exhaust and upstream O2 sensors probably caused the engine control module to recognize dead cats.

How can an engine rev to 6K rpm with plugged secondary cats? The secondaries were only partially plugged and exerted backpressure on the exhaust that in turn affected the state of the cylinder contents during induction, which in turn affected the stoichiometry. This was enough to signal a misfire. The misfire was not due to the crankshaft sensor data feed but the O2 data feed from the upstream O2 sensor. Most techs will not diagnose any plugged exhaust components if the engine can rev freely. In other words, they way the secondaries failed did not provide enough evidence to a tech to quickly diagnose the issue. Major issue.

Lessons learned:

I needed to change my clutch last year. If I knew then about the weakness in Nissan cats, I would have changed them out then and save a lot of labor cost. Cats need to be taken out to change the clutch.

Nissan warrants the cats for 8 years/80k miles. Knowing what I know now, I would have changed spark plugs before 8/80 to see if the cats died. If so, the cats would be replaced under warranty.

It is troubling that partially plugged secondary cats can rob an engine of so much power. The loss is so subtle and slow that I did not recognize it. If you think your 4.0 has lost a lot of mojo, break the primary/secondary cat flange, run the truck, and see if the lost power reappears.
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VERY interesting. Thank you for your analysis.
Probably hard to say now, but perhaps your primaries did not need replacing?
Could secondaries have been replaced as opposed to gutting them? Or, maybe using aftermarket secondaries?

Edit: had you ever utilized Nissan's fuel system cleaning method where the entire engine is run on the cleaner in no fuel/gasoline is utilized? My dealership service manager explained that this method helps to recondition the cats as well as cleaning the injectors/etc...
Primaries dead as a doornail

The primaries were dead. In examining them once off the truck, there was some honecomb damage. I am not one to go offroad or jump the truck so all the damage is due to wear and tear.

The secondaries treat a pollant other than hydrocarbons (primaries). I live in a State that requires emissions testing so gutting the secondaries was not a solution. I did use aftermarket secondaries.

My tech did try to clean the cats but to no avail. They were too far gone. Your dealer is talking about a cleaning method that may work if done regularly. I am wary of dealers and this method sounds like a revenue enhancement method. However, if they offer an extended warranty, it may be worth it.
Glad to hear you solved the issue. I'd love to know the relationship between changing plugs and emmisions codes.

What I do know is you don't want to run with bad primary cats for any length of time. They are close enough to the heads that the broken catalyst gets scavenged into the cylinders and scores the walls and pistons. Not a Nissan specific issue either.

Also, Scotty Kilmer is very biased and if I'm honest, full of ****. According to him, if it isn't a Toyota.. It sucks!
Ryno 7. Tell me what you really think. LMAO. ?
"The weakness in Nissan cats"? I'm sorry it happened to you but it's not that common.
Just so I know.. what do I look for if they start to go bad, will the cel come on or is there symptoms before that?
Cats will die without warning

There is no CEL code to warn of incipient primary cat failure. If you have a scan tool, you can monitor the O2 levels and track the differential. But most people will not go through this bother. In my case, all I did was change the sparkplugs and voila! dead cats.

Secondary cats are not monitored at all so you are flying blind until they fail.
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Just so I know.. what do I look for if they start to go bad, will the cel come on or is there symptoms before that?
Strong odour from the exhaust and worse fuel economy than usual. More likely, your o2 sensors will detect the issue and trip a CEL. Some times a failed converter will rattle on acceleration, tapping it with a hammer will produce the same sound. But again, the CEL should be on by then.
I'm sleuthing here, so bear w/ me. Wanting to garner/glean as much info here as I can.

CT_Nismo, did you get a good look at your OEM spark plugs' condition when they came out? I could see how poor firing plugs might begin this process of primary cat degradation...though I'd hope a code would be thrown. If primary cats were already degrading, then they would surely contribute toward plugging the secondary cats?

Were your OEM/factory NGKs' platinums? If so, were they also a 105k recommended lifespan? For some reason I was thinking the evolution to Iridiums extended the service life to 105K? Very possible I'm wrong on this one.

A thread like this one is very worthwhile...making CF a valuable tool for understanding complicated scenarios like this sequence of events.
Pictures of old and new spark plugs

The replacement spark plugs are LFR5AIX-11 4469 and are Iridium rather than OEM Platinum. Could this substitution be the issue that caused the cats to die within hours of install? Not logical but my mind was worried so I took out the new plugs after 2 months and compared them with the old Platinums. See the attached pictures. Yes, I did keep the retained plugs in cylinder order.

It seems to me that the few hours it took for the P0420/430 to go live is because the codes were pending.

Could the demise of the primaries be due to the plugging of the secondaries? Yes, it's possible. But what is the theoretical pathway? I retained the old upstream O2 sensors. I will post pictures of these later on and we can discuss.
There is no CEL code to warn of incipient primary cat failure. If you have a scan tool, you can monitor the O2 levels and track the differential. But most people will not go through this bother. In my case, all I did was change the sparkplugs and voila! dead cats.

Secondary cats are not monitored at all so you are flying blind until they fail.
Think I’ll keep my plugs in their, l had thought about changing them but I’ll wait till it warms up again...just in case!
Converter failures are fairly common on these vehicles, including the R51 Pathfinders and Xterras, but it seems to be hit or miss on the vehicles that have problems and I think the earlier ones are more prone than the 2007 and later, but that's just speculation from my mechanical experience and from the feedback I've heard on several Nissan forums. For example, my 2008 Pathfinder has 235,000 miles on it and still has the original catalytic converters on it (along with the rest of the exhaust). It came with the Laser Iridiums from the factory and I replaced them with the Laser Platinum 6240's at 100,000 and 200,000 miles. My 2006 Pathfinder has a different story. It originally came with the Laser Platinum 6240's from the factory which were replaced at 100,000 miles; it currently has 190,000 miles on it. I purchased the vehicle with 84,000 miles on it and the dealer had just replaced the left, upstream catalytic converter and upstream oxygen sensor (both genuine Nissan parts). At around 145,000 miles, it started triggering a P0420 code for the right converter, so, at 150,000 miles, I replaced the right, upstream converter with a Walker Ultra direct-fit converter. I also replaced the exhaust manifold with Doug Thorley shorty headers and replaced the rear converters with Doug Thorley mid-pipes, plus replaced the upstream, right, oxygen sensor (NTK brand). At around 175,000 miles, intermittently, I started getting a P0430 code for the left, upstream converter and it has been triggering more frequently as of late (I just erase the code when it pops up). Normally, this code doesn't indicate a clogged converter, rather an inefficient converter, meaning it is no long efficiently breaking down the exhaust emissions as per the ECM's inputs from the upstream and downstream oxygen sensors. It is usually safe to drive with inefficient long as they are not restrictive or clogged, which would result in drivability issues in most cases. The usual causes for a bad converter are excessive unburned fuel, either due to misfire, an over-rich condition or an oil burning engine. It's not uncommon on to hear of vehicles that have had an ignition misfire, such as that due to a bad coil pack, which is soon followed by catalyst efficiency trouble codes.
Let's go back to the failed converter issue seemingly more common on 05-06 models of the V6 Pathfinder/Frontier/Xterra... A friend of mine also had a P0430 code on their 130,000 mile Frontier. It was all stock, including the factory exhaust. One thing I always wondered about is why are the 2005 and 2006 models with the VQ40DE engine rated at 170 HP and 2007 and later are rated at 266 HP? Looking at my own 2006 and 2008 Pathfinders, I also notice that gas mileage is typically 1-2 MPG better on the 2008 model. Engine specs, including the cams, are the same between the two, as well as the intake system, tire size and transmission. My 06 does have the AUTO mode transfer case compared to the 08's manual transfer case and the so-called "restrictive Y" of the exhaust system is a little better design on the 08, but how much difference that makes, I don't know. They still shouldn't affect the factory power rating of the engine. So, either they incorrectly rated the engine horsepower and corrected it in 2007, or, more likely, they changed the fuel management software in 2008, perhaps making it run a little leaner than the previous software and better for the life of the converters? I don't know, but it's just my theory and food for thought!
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All Nissan Frontiers since 2005 with the 4.0 L engine have been rated for about 260 hp.

A search of Rock Auto’s catalytic converters shows the Eastern 40711/40710 for left and right converters for model years 2005-2016. It stands to reason that the OEM converter has not changed in this timeframe. It is very strange that Rock does not show any converter offerings for model year 2017 and later.

While it is OK to run with a dead converter (P0420/0430) the truck will fail inspection in most States.

My angst against Nissan concerning the recent all converters failure in my Frontier is how I discovered the failure situations. It should not be that changing the spark plugs uncovers the need to replace primary converters. It also should not be that slightly plugged secondary converters induce the motor control module to throw P0300 codes which do not provide diagnostic cookie crumbs back to the secondaries (cause).

I want to re-emphasize the magnitude of power gain I got by replacing the secondaries. It is like putting an old swayback mare in the barn and the next day a young filly is in its place. The hp loss happened over a long period of time thereby escaping my notice.
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smj999smj - The difference is going from O2 sensors to air/fuel sensors.
Hello All: I have been reading on this topic and read several threads and all of them point into different directions. My truck is throwing P0430 since yesterday on Bank 2 which means driver side. Question is what should I do? Should I take it to the shop to help them diagnose? Should i buy both cats and replace them along with O2 sensor? If so which brand are better other then the OEM? OEM is not affordable. Please help.
So, I had a simlar issue with my truck recently, and here's kindof how mine went. I was driving down a gravel road one day and hit a chunk of ice/dense snow (right after a snowfall) that kicked my entire exhaust system backwards and tore the rusted weld of the secondary cats out of the fitting for the primary cats. The fittings were still bolted together but the weld had failed and it was basically running super loud, (just one primary cat between the engine and the outside atmosphere) so I had my exhaust guy weld it back in place. The exposed cat elements appeared to be 10-4 and visually in good ocndition.

A few days later I suddenly had P0300 mult cyl misfire! Oh **** what's happening now. I took it to a shop and said I dunno what's up, and told them about the above story, they began diagnostics and short version of the story later I had to get the spark plugs and coils replaced. once that was done I was sorely dissapointed to find that I still had a p0300 code and the vehichle was VERY sluggish/would not accelerate under higher RPM (no power) seemed to run fine a lower RPM, (I could baby it and it ran fine) so I broke down and took it to nissan to pay my dues for the correct diagnosis. $185 later they had jacked it up took off the secondary cat and showed me a broken primary cat element, and threatened to charge me $2500 to fix it.

I laughed at their attempt to ensure I would not allow them to fix my truck, and told them I'd be driving my limping truck back home with the broken cat, as gingerly as possible. They also advised me to get it fixed or it would get catalyst into the cylinder, and **** up the motor. They also made a big note in the Nissan Database so they could make sure everyone knew I was told to fix it.

I had a private assistant help me remove the cats so that we could make sure that was the problem... It was. no more codes after that, and the power came right back.

I have ordered new primary cats for replacement, and am finishing replacing all my o2 sensors.

When I was a teen I had a Mazda B2600 and it had a similar issue, it was always overheating, always felt under powered, had a blown head gasket, and never ran quite right. (in hindsight it probably had blown piston rings too) we eventually opened up the cats and discovered why it was always overheating. The primary cat looked like someone had poured black pitch tar all over it and had burned in place clogging up the center of the Cat. After that it ran Beautifully!

The point is that IMHO cats are good for exactly three things. F***ing up your motor, throwing CEL codes and catching mice in barns. I am only installing my brand new cats on my truck, so that when it goes to the Nissan Dealership for a checkup with the next owner, they can look to see if I replaced the cats, and see that I did.
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CTNismo, it's interesting that you had your clutch done in the time frame leading into the onset of these problems. I did as well, although my timing was much closer together. I had clutch done at 98k in July '20, and then did plugs at 103k in August '20. The clutch was a job that I could not do myself, and I know that the shop that I took it to did not replace the crush rings when they removed and replaced the primary cats in order to pull the bell housing back. I started with P0430 (driver primary, reduced efficiency). I did a leak check with reversed vacuum cleaner in tailpipe and soapy spray and found a leak at the flange between primary and secondary. Because of the pulsing of the exhaust and sucking some exhaust back in during intake (reverse flow) this can get outside air into the system before the downstream O2 sensor throwing off its O2 reading. It can also pull outside air back to the A/F sensor before the primary cat. This will cause a false lean reading that will make the control loop enrich the mixture. This is especially true at idle when the velocity of the outbound exhaust is lowest. This situation is of course not good for the cats. If you are not believing (I wasn't) check this: How an Exhaust Leak Affects Wideband/O2 Sensor Readings

Since I had to tear it apart to replace the crush rings anyway, I replaced the primary cat with a Walker, both sensors and both crush rings. Cat element looked very clean and intact physically, so I'll keep it as a backup for later. Leak check looked good afterwards. Still observing the whole situation. I am monitoring downstream O21 ad O22 with a Scan Gauge II.

To get 5k in one month I do a lot of camper towing with this truck and during this whole episode (but before P0430) I got turned on to running 89 octane when towing. This is, of course against the manual, which calls for 87. I find that when towing it seems to give better power at lower RPMs, especially for hill climbs. My reading on this has been equivocal with some folks saying that running higher octane than the engine is designed for can reduce cat life and others saying that it is not related.

I have not come up with a good theory on the potential involvement of the new plugs.
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Really interesting postulate w/ the clutch job and subsequent exhaust/emissions issues.

LongJohn, is your hilly towing at higher altitudes - IE mountainous, or just hilly?
Did you only replace one side w/ a Walker, or both?
Most of the "mountainous" parts of my trips have been in TN (I-40, I-65), KY (I-65) and PA (I-81). I say "mountainous" knowing that these are not real mountains like CO, etc. On these trips, there is a lot of up/down, sudden climbs and dead drops. I find that I don't have to anticipate the climbs as early and I rarely have to downshift into 4th when I run the 89. I can hold 60 in 5th when climbing, and that is in the lower end of 5th around 2k RPM, where it begins to want to lug. I do not use 6th when towing.

I replaced only the driver's side with the Walker. No P0420 yet, and O12 (Bank 1, downstream O2) readings look OK. I leak-checked and tightened the flanges on that side.
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