P0430? What should I do?

[T4R03]

I have a 2003 4Runner Sport with 180k miles on it and I've been having this p0430 code on for a while now. AllData shows me how to test the vechile and that it can either be a cat, o2 sensor, or an A/F Sensor. I want to know your guys experience with this code because the cat is expensive to replace... the A/F is not only expensive but it's a whole b**** to get out by the position it's at. I want to change out both the o2 Sensors but I just want to know that's the issue. Anyone have experience with this and can help on how to fix it?

 

[lightfreak]

First thing to look for are exhaust leaks. Even a small leak can throw this code.
There’s different tests you can use like running seafoam to check the smoke leaking or running a vacuum in reverse to blow air into the exhaust pipe.

Next is to check the temps of the exhaust pipes pre and post cat after a long drive. Amazon sells IR thermometers for $20. If it’s hotter pre cat then it’s restricted and needs to be replaced or you can try cleaning it.

If it’s not the cats , next would be to change the downstream O2 sensors. Change them both and only use either Denso or Toyota OEM sensors.

Upstream AF sensors shouldn’t be causing this code.

There’s a few long threads on here with lots of user experiences, search for P0420 and P0430.

 

[T4R03]

First thing to look for are exhaust leaks. Even a small leak can throw this code.
There’s different tests you can use like running seafoam to check the smoke leaking or running a vacuum in reverse to blow air into the exhaust pipe.

Next is to check the temps of the exhaust pipes pre and post cat after a long drive. Amazon sells IR thermometers for $20. If it’s hotter pre cat then it’s restricted and needs to be replaced or you can try cleaning it.

If it’s not the cats , next would be to change the downstream O2 sensors. Change them both and only use either Denso or Toyota OEM sensors.

Upstream AF sensors shouldn’t be causing this code.

There’s a few long threads on here with lots of user experiences, search for P0420 and P0430.

Awesome sounds good... thank you for the advice. I will do this and just hope that it's not the cats... because money is tight right now lol

 

[That_Titanium_4RNR]

I had P0156 and P0157. It was a bad bank 2 sensor 2. Replaced with Denso unit and its been fine for over 200 miles now.

 

[mar5168]

First thing to look for are exhaust leaks. Even a small leak can throw this code.
There’s different tests you can use like running seafoam to check the smoke leaking or running a vacuum in reverse to blow air into the exhaust pipe.

Next is to check the temps of the exhaust pipes pre and post cat after a long drive. Amazon sells IR thermometers for $20. If it’s hotter pre cat then it’s restricted and needs to be replaced or you can try cleaning it.

If it’s not the cats , next would be to change the downstream O2 sensors. Change them both and only use either Denso or Toyota OEM sensors.

Upstream AF sensors shouldn’t be causing this code.

There’s a few long threads on here with lots of user experiences, search for P0420 and P0430.

As a master technician with over a decade of experience, this is not necessarily good advice.

A clogged cat usually results in sulfur smells and hard starting. If you have neither, it's more likely the catalyst substrate has been used up.

Barring no exhaust leaks between the end of the cat and the downstream sensor, you very likely have a bad cat.

A bad secondary O2 sensor will throw its own code.

So, if you don't have an exhaust leak and additional codes for a downstream O2 sensor, you're very likely looking at a bad cat. Therefore, replacing your O2 sensors will only result in wasted time and money.

All this said, and over a decades worth of experience wrenching professionally, I'd place a gentleman's bet of $1 that you have a bad cat and I feel very good about placing this bet.

With a bad cat you have two options; replace the cat, or google spark plug antifoulers in conjunction with a bad cat and follow the steps at your own risk.

 

[lightfreak]

As a master technician with over a decade of experience, this is not necessarily good advice.

A clogged cat usually results in sulfur smells and hard starting. If you have neither, it's more likely the catalyst substrate has been used up.

Barring no exhaust leaks between the end of the cat and the downstream sensor, you very likely have a bad cat.

A bad secondary O2 sensor will throw its own code.

So, if you don't have an exhaust leak and additional codes for a downstream O2 sensor, you're very likely looking at a bad cat. Therefore, replacing your O2 sensors will only result in wasted time and money.

All this said, and over a decades worth of experience wrenching professionally, I'd place a gentleman's bet of $1 that you have a bad cat and I feel very good about placing this bet.

With a bad cat you have two options; replace the cat, or google spark plug antifoulers in conjunction with a bad cat and follow the steps at your own risk.

I speak from experience , I own the same car as the OP and had the same problem code p0420/p0430, twice in the last 2 years in fact. First time was cleared up by changing the downstream O2’s and second time was an exhaust leak a year later. Cats haven’t been touched and many on here have had similar experiences. There’s several long threads on this trouble code. And if I listened to mechanics like you I’d be several grand in the hole.
And you’re encouraging expensive cat replacement without seeing the truck?
It’s no wonder most on here do their own work.
It may very well be the cat in the end but how about we try to save the guy some money first?

 

[Terminator03]

I speak from experience , I own the same car as the OP and had the same problem code p0420/p0430, twice in the last 2 years in fact. First time was cleared up by changing the downstream O2’s and second time was an exhaust leak a year later. Cats haven’t been touched and many on here have had similar experiences. There’s several long threads on this trouble code. And if I listened to mechanics like you I’d be several grand in the hole.
And you’re encouraging expensive cat replacement without seeing the truck?
It’s no wonder most on here do their own work.
It may very well be the cat in the end but how about we try to save the guy some money first?

I agree, and in my experience CATs only go bad if they’ve had problems with extra unburned fuel being ignited inside by heat from the CAT. This usually caused by failed coils, or other ignition/fuel related problems. CATs don’t typically just wear out. They either get plugged, or internally damaged by raw fuel as described. OP, exhaust leaks are super common on these trucks, and cause a lot of these problems as others have pointed out. That being said, if money is an issue AND you think it’s actually the a CAT that’s bad, you can certainly try the anti-foulers on the rear sensors. It usually takes 2 per side, but it will work in most cases. I would exhaust (no pun intended, lol) all of the diagnostic options first though, to try to correct it if possible. Good luck, and please update once you have it solved.

 

[mar5168]

I speak from experience , I own the same car as the OP and had the same problem code p0420/p0430, twice in the last 2 years in fact. First time was cleared up by changing the downstream O2’s and second time was an exhaust leak a year later. Cats haven’t been touched and many on here have had similar experiences. There’s several long threads on this trouble code. And if I listened to mechanics like you I’d be several grand in the hole.
And you’re encouraging expensive cat replacement without seeing the truck?
It’s no wonder most on here do their own work.
It may very well be the cat in the end but how about we try to save the guy some money first?

If you listened to me you'd have a vehicle that was fixed properly the first time.

Please re-read my post to answer your first question. I didn't recommend anything. I did, however, provide factually accurate statements, my hunch as to what's causing the problem, and information on how to fix it.

Do you have any empirical data to back up your claim that replacing downstream O2 sensors is the fix for a catalyst inefficiency code?
Remember, correlation does not equal causation.

I know this may be hard to understand, but your p0420 and p0430 were not fixed by replacing downstream O2s. The codes simply never set after you cleared them when you replaced the sensors. I do, however, have no doubt that your exhaust leak could have caused catalyst inefficiency codes as this is very common.

Because of the sensitive nature of catalyst inefficiency code logic (dictated by the gov, and different in California), every dealership I've worked for has a policy of clear and wait for re-code on P0420 and P0430. Interestingly enough, I'd say less than 1/4 of vehicles would re-code and require additional diagnostics.

As a side note, 99% of career technicians I've worked with are looking out for the best interest of the customer. I, in no way shape or form am trying to dupe people into pointlessly spending money. Most of us take pride in accurate first time diagnosis and repair (a common metric in the industry). Stating I'd cost you "several grand" and am part of the reason people work on their own vehicles, shows your misunderstanding for the industry, my post, and myself personally.

I could very easily make the argument that listening to somebody uneducated in the field of automotive repair that's recommending replacing downstream O2 sensors for a catalyst inefficiency code is the easiest way to waste "several grand", require multiple repairs, and is reason to have a professional look at it.

I agree, and in my experience CATs only go bad if they’ve had problems with extra unburned fuel being ignited inside by heat from the CAT. This usually caused by failed coils, or other ignition/fuel related problems. CATs don’t typically just wear out. They either get plugged, or internally damaged by raw fuel as described. OP, exhaust leaks are super common on these trucks, and cause a lot of these problems as others have pointed out. That being said, if money is an issue AND you think it’s actually the a CAT that’s bad, you can certainly try the anti-foulers on the rear sensors. It usually takes 2 per side, but it will work in most cases. I would exhaust (no pun intended, lol) all of the diagnostic options first though, to try to correct it if possible. Good luck, and please update once you have it solved.

I'm glad that you're both aligned on your logical fallacies, but allow me to provide some actual facts as opposed to the tribal knowledge being passed around. Catalysts do, in fact, go bad over time. The catalyst substrate is made of platinum, palladium, and rhodium. Heat cycling of the substrate causes it to break down over time and the microscopic parts or platinum, palladium, and rhodium get shot out of your exhaust. So yes, prolonged loss of substrate material does mean the catalyst becomes less efficient over time, which obviously, can result in the codes being thrown.

 

[Terminator03]

If you listened to me you'd have a vehicle that was fixed properly the first time.

Please re-read my post to answer your first question. I didn't recommend anything. I did, however, provide factually accurate statements, my hunch as to what's causing the problem, and information on how to fix it.

Do you have any empirical data to back up your claim that replacing downstream O2 sensors is the fix for a catalyst inefficiency code?
Remember, correlation does not equal causation.

I know this may be hard to understand, but your p0420 and p0430 were not fixed by replacing downstream O2s. The codes simply never set after you cleared them when you replaced the sensors. I do, however, have no doubt that your exhaust leak could have caused catalyst inefficiency codes as this is very common.

Because of the sensitive nature of catalyst inefficiency code logic (dictated by the gov, and different in California), every dealership I've worked for has a policy of clear and wait for re-code on P0420 and P0430. Interestingly enough, I'd say less than 1/4 of vehicles would re-code and require additional diagnostics.

As a side note, 99% of career technicians I've worked with are looking out for the best interest of the customer. I, in no way shape or form am trying to dupe people into pointlessly spending money. Most of us take pride in accurate first time diagnosis and repair (a common metric in the industry). Stating I'd cost you "several grand" and am part of the reason people work on their own vehicles, shows your misunderstanding for the industry, my post, and myself personally.

I could very easily make the argument that listening to somebody uneducated in the field of automotive repair that's recommending replacing downstream O2 sensors for a catalyst inefficiency code is the easiest way to waste "several grand", require multiple repairs, and is reason to have a professional look at it.




I'm glad that you're both aligned on your logical fallacies, but allow me to provide some actual facts as opposed to the tribal knowledge being passed around. Catalysts do, in fact, go bad over time. The catalyst substrate is made of platinum, palladium, and rhodium. Heat cycling of the substrate causes it to break down over time and the microscopic parts or platinum, palladium, and rhodium get shot out of your exhaust. So yes, prolonged loss of substrate material does mean the catalyst becomes less efficient over time, which obviously, can result in the codes being thrown.

I didn’t say they NEVER go bad, just that they typically last well over a 100,000 miles, barring any engine issues causing early demise such as the examples I mentioned. I actually had one go bad at 60k miles due to a coil related misfire on another vehicle. My intent was to not have the OP just throw an expensive CAT replacement on without doing due diligence, as it could very well be something much simpler, and cheaper to repair.

 

[gaber6]

My p0420 cleared and stayed off after I replaced my exhaust donut and O2 sensor.
I was having to clear it every day. I assume it was one or the other causing the problem, but had purchased the sensor already.
Check the exhaust donut first if you want a cheap fix. I couldn't even hear a leak, but it was smashed so thin that there wasn't tension on the springy joint.

 

[2003-4x4runner]

I had the same issue and I tried CAT clean and it helped out for awhile. I also replaced all the Co2 sensors. 6 months later, the PO420 code came back and it wouldn't go away. So I ended up buying a new CAT and I haven't had any issues since and that was 2 years ago. Parts and labor was $1000.00 at a local shop in Nor Cal.

If you do a search on T4R, you'll find that this issue seems to be common on the 4th Gen V6. Good luck.

 

[mar5168]

I didn’t say they NEVER go bad, just that they typically last well over a 100,000 miles, barring any engine issues causing early demise such as the examples I mentioned. I actually had one go bad at 60k miles due to a coil related misfire on another vehicle. My intent was to not have the OP just throw an expensive CAT replacement on without doing due diligence, as it could very well be something much simpler, and cheaper to repair.

You're right, you didn't say "never", you said "only." Which in context of the conversation, means the exact same thing.

I had the same issue and I tried CAT clean and it helped out for awhile. I also replaced all the Co2 sensors. 6 months later, the PO420 code came back and it wouldn't go away. So I ended up buying a new CAT and I haven't had any issues since and that 2 years ago. Parts and labor was $1000.00 at a local shop in Nor Cal.

If you do a search on T4R, you'll find that this issue seems to be common on the 4th Gen V6. Good luck.

I believe this proves my point.

I'll never understand why some on this forum believe that catalysts don't fail and resort to replacing known good parts as a solution. The stigma and false information about P0420 and P0430 codes around here is rampant.

 

[kosan]

Same issue. Tried doing the cheap fixes first. Gas cap, then couple hundred miles later, would appear, then did the O2 sensors one at a time. Thought it was fixed but code would show up again. Finally did the cats Worked. haha

 

[duffdog]

After a catastrophic accident when I accidentally drove into the ocean and then huge backfiring sounds came from the catalytic converters, the 0420 code was set. This was obviously caused by explosions blowing part of the grid apart when I got saltwater in the engine. Rather than fork out thousands of dollars for a new driver side cat or risk getting caught with sensor spacers (literally everyone gets caught during the smog check with defoulers in Northern CA nowadays) I figured out how to make a completely blown or removed cat read as a perfectly operating cat and never set a check engine light ever again. Note that there are several "o2 simulators" which are little more than a feeble attempt at delaying the upstream cat signal by 90 degrees. What you really want is a smoothed output of the correct voltage which still responds to the upstream o2 sensor inputs in both the correct time base and reports the correct voltage.

So here is what to do: solder a 6.7K resistor in series with a 4.6uF low esr capacitor onto the blue sensor return wire and slide the wire heat shield back over your circuit so that it looks like nothing at all has been done to the sensor or the wires.

There are several posts on the interwebs showing an obviously incorrect circuit placing a capacitor in parallel with the sensor element as an RC filter...This will definitely not work on a 4th gen as the computer expects constant current and no change in VI relationship across the sensor. The computer detects your wierd RC filter circuit and sets a code stating the computer is bad and now you have created an altogether different problem. Which is lame. What you want is a circuit that acts as an adder, meaning you simply add a negative voltage to whatever voltage the sensor is reading. Unfortunately this will only work with completely blown or removed cats and will throw another code if you use a modified sensor with a good cat.

I am going to smog my truck tomorrow and see if it passes. The rear cat is still installed so hopefully that cat has enough material left to filter out the pollutants. Anyone want to place bets that I can pass smog with an exploded pre-cat?

 

[Oneluv13T4R]

After a catastrophic accident when I accidentally drove into the ocean and then huge backfiring sounds came from the catalytic converters, the 0420 code was set. This was obviously caused by explosions blowing part of the grid apart when I got saltwater in the engine. Rather than fork out thousands of dollars for a new driver side cat or risk getting caught with sensor spacers (literally everyone gets caught during the smog check with defoulers in Northern CA nowadays) I figured out how to make a completely blown or removed cat read as a perfectly operating cat and never set a check engine light ever again. Note that there are several "o2 simulators" which are little more than a feeble attempt at delaying the upstream cat signal by 90 degrees. What you really want is a smoothed output of the correct voltage which still responds to the upstream o2 sensor inputs in both the correct time base and reports the correct voltage.

So here is what to do: solder a 6.7K resistor in series with a 4.6uF low esr capacitor onto the blue sensor return wire and slide the wire heat shield back over your circuit so that it looks like nothing at all has been done to the sensor or the wires.

There are several posts on the interwebs showing an obviously incorrect circuit placing a capacitor in parallel with the sensor element as an RC filter...This will definitely not work on a 4th gen as the computer expects constant current and no change in VI relationship across the sensor. The computer detects your wierd RC filter circuit and sets a code stating the computer is bad and now you have created an altogether different problem. Which is lame. What you want is a circuit that acts as an adder, meaning you simply add a negative voltage to whatever voltage the sensor is reading. Unfortunately this will only work with completely blown or removed cats and will throw another code if you use a modified sensor with a good cat.

I am going to smog my truck tomorrow and see if it passes. The rear cat is still installed so hopefully that cat has enough material left to filter out the pollutants. Anyone want to place bets that I can pass smog with an exploded pre-cat?

Well....
did it end up passing the smog test?

 

[BlackWorksInc]

For what it's worth, it's not uncommon to see a TWC (Three-Way Catalytic Converter) degrade/begin to fail after 150k after normal use. That's not to say they can't make it over 200k without issues, just that there's a lot of variables at play and seeing one set a DTC for efficiency at 180k is not surprising or out of character from what I have seen.

The main way the system detects the efficiency of the TWC is by checking it's ability to store oxygen by using the AFR & O2 Sensors, as well as it's own internal calculations based off some other ECM inputs (that's something I don't think you can really see the ECM doing, only the result of what it comes up with.)

I just ran into this with an old 2nd gen Prius that had something over 200k, it came in originally with just a P0171 (System Too Lean- Bank 1). Looking at the MAF Sensor (useful to look at on many vehicles with similar issues, though on a hybrid it's a bit of a pain), AFR Sensor, O2 Sensor, and Fuel Trims; it was running too lean (something like 28% Long Term Fuel Trim); vehicle ran well for an old Prius and the customer hadn't noticed anything too weird beyond the MIL. Inspected for any intake leaks and exhaust leaks and didn't find anything, did find the MAF Sensor to be rather dirty and have some fluff on it (likely from someone not clearing the air box properly before throwing a new filter in it), cleaned the throttle body and any residual oil in the intake as a courtesy. Cleared DTCs, set vehicle in Check Mode (One-Trip Detection Mode) and gave her a quick test drive, within two miles LTFT dropped from 28% to just 4~6% (we like to see +/- 10% in general for a normal vehicle). Told the customer to have a nice day and keep an eye on the vehicle for any reoccurrence/odd behavior.

They came back a week later with only a P0420 (Catalyst Below Efficiency- Bank 1), not entirely surprised with that outcome; but wait, why didn't it set a DTC the first time it came in you might ask? Well, because the P0171 beat the P0420 to the punch; the moment the DTC got set it stopped monitoring the Catalyst and thus it never bothered to notice the catalyst failed its monitor. So we start with the usual stuff, verified MAF, AFR, and O2 sensors are functioning as designed, our fuel trims were right where we wanted them to be; so now we're most likely looking at a TWC failure (possibly due to age, possibly due to running lean too long, it doesn't matter at this point on a 2008 Prius with 200k+ miles). Now before recommending a catalytic converter and calling it a day I did have some minor frustration with the AFR and O2. The sampling rate on a TIS Techstream through the OBDII connection leaves a bit to be desired in general, particularly on older vehicles; but in this case I wasn't particularly happy with how long the AFR and O2 sensors took to warm up and start signaling properly, they were a bit too sluggish even by the FSM's standards (though oddly did not set any DTCs) and the signals looked "okay-ish" but still slightly off.

So at this point from a gut/experience perspective I'm leaning on a TWC and two sensors to both be safe and ensure there isn't a 3rd visit from this customer. To verify my gut feeling, I should have looked at the prior test result from the Catalyst Monitor; but monitor results get forgotten/overlooked by a lot of technicians (myself included) because we can usually see real-time Data List that will point us in the right direction. But in this case since I was a bit skeptical of the sensors I went ahead and cleared the DTCs, set the vehicle in Check Mode (this is a really useful feature) and test drove it for about 10mi while watching the Data List. All sensor readings, fuel trims, and such were relatively good; though again, the sensors were still a little "off" until they fully warmed up. After the test drive the Catalyst Monitor reported "Passed" with a value of ".032"

I can't really tell you what .032 is being measured in (ppm, g, or maybe bushels lol?), but it doesn't matter. What matters is that the Monitor reported: Result- Passed, Measured- .032, Min- .031, Max- .999; this tells us we have what is often referred to as a "Borderline Catalyst" one that is just on the failure threshold and will report good some days and bad other days. Now that combined with the other information we've gathered makes me more confident in recommending a TWC replacement because it's failed/failing, as well as a new AFR & O2 Sensor due to age/mileage/degradation affecting their responsiveness/efficiency. It's an expensive repair for a customer, but I am fairly confident with my recommendations. Customer approved the repairs and the new sensors are much better as warming up and giving more "stable" readings, new Catalyst passed it's monitor with flying colours.

Now the reason I even bothered to post all this pedantic story is to show how annoying and generally boring Catalyst failures can be. You do enough of these types of diagnosis and repair in the industry long enough and you start to see a consistent pattern that you can rely on 9/10. Only a P0420/P0430 DTC is set on an older (150K, 10yr+) vehicle, MAF, AFR, and O2 sensors seem to be reading well; Fuel Trims look relatively okay, etc. then it's the catalyst. That's a "Gut Feeling/Experience Based" diagnosis that most experienced techs can pop out in under 10min from just the FFD (Freeze Frame Data) and/or a quick peek at the Data List; most of the time you don't even need to double check anything. In the case of the Prius, I could possibly have omitted the sensor replacements, but I have come across a handful of instance on fairly old vehicles where we replaced the catalyst and one or more sensors trip a DTC for something that ends up being caused by a sluggish/degrading sensor; so these days I will usually at the very least throw a rear O2 sensor in with a Catalyst Replacement out of habit (in the case of this Prius the readings were slightly weird so I dug further to verify that it wasn't possibly just the sensors being weird causing the DTC).

So take the above however you want, you can say I and other seasoned technicians are lazy because we see that DTC and a high mileage vehicle and just go "you need Cats" without explaining further and the whole above post is just justification for our laziness. Or you can see how someone forms a "Gut Feeling/Intuition" by seeing many of these similar cases and learning what information is important/worthwhile and what isn't to trim down their diagnostic time and better serve the customer and reduce the amount of times they have to come back for repairs and/or labor their charged (i.e. in the case of the Prius, I just rolled sensor replacement into .5hrs for both since I was already replacing the catalyst; the .5hrs actually worked in that customer's favor; I had to pull the exhaust manifold out because the B1S1 AFR Sensor stripped out the bung coming out despite my best efforts so I had to remove the manifold to try and chase it and do my best to save the manifold for the customer rather than just recommending a new one since they were so nice to trust us with such an expensive repair.) Or we could just charge the customer diagnostic time + repair for each visit they do and rack up billable hours (usually charge at least 1hr flat diagnosis fee and 1hr flat sensor replacement fee unless it's not easy to get to; so you can see where that adds up fast for a customer.)

 

[4r-4ever]

now that we are talking CATS, i just got a p0420 code. is this cat on the passenger side for p0420? checked for leaks and found a leak between the first cat and the second cat. there's a little bit of leak at the exhaust manifold.

i agree, when doing this expensive repair, it's best to replace the af/o sensor at the same time. i think i have a ptsd working with exhaust. lol!

by the way, i have 155000 miles now.

 

[Stuffman]

P0430 Passenger AF/O2

Had an P0430 code pop up. Cleared many time and the code pop's up again pretty quickly. Never looked at O2 sensor data. Had a Denso O2 sensor sitting around so I figure to put it in. It has about 60 miles on it. I can not get the P0430 code to come on. Will update after a few hundred miles more.

 

[Miranthis]

At about 310,000 miles i started throwing p0420 and then shortly thereafter p0430....i tried Cat Clean, lacquer thinner, looking for exhaust leaks, replacing a downstream O2, hoping, praying, cussing, bargaining with God, watching nearly every relevant YT video, hours of techstream data dives, etc. And then bought some Canadian manufactured aftermarket cats, installed them with new hardware, gaskets, and replaced both A/F and the remaining original O2 sensor , all with new Densos...

Joy lasted about 10,000 miles then P0420 and P0430 came back. Tech stream each time showed way too much activity in the downstream sensors and the temperatures were all wrong pre vs post cats.....finally bought factory cats (495 each) and did the installs myself. NOW techstream shows proper o2 system function.....and i am at 349,742 miles.

Moral is, trust the numbers and data, Cats DO wear out. If you need replacments, just do factory ones and dont look back.