Low on production value, but really, really high on clear, usable content. Thank you. Was trying to understand the live readings I was getting and this explained it perfectly and clearly. Great video.
As usual you have done a great job of explaining the root cause. I love your videos and you. I got this code and I just came to your channel and I found my answer. You are a GURU.
I have watched many videos on this site and have done alot of reading regarding auto repair. I just wanted to say thanks for the video. It was very informative and because of the video I was able to gain some knowledge about the diagnosis of these particular diagnostic codes. The video was short and to the point and covered everything that I needed to know. Keep up the good work !
It's really nice to have an explanation that is detailed enough to make sense. The code is encompassing at least three different components, as well as a number of issues such as leaks. Being able to look at the signal and understand what it is doing and should be doing is really the only responsible thing to do. Mechanics that either through laziness, lack of proper education and/or greed, can manipulate the test and put the customer through a lot of expense. I am not a mechanic, but did electronics repairs and felt it was my responsibility to find and repair, for the least expense, the right problem and not just throw a bunch of parts at it and hope one works.
Just wanted to share this guy's issues with this and testing. Because he had issues with various parts, it made the video even more informative. Hope it adds to this one. ua-cam.com/video/YL1c-_qLK4Y/v-deo.html
Great video, being an electrical engineer by degree, I immediately understood your explanation using the waveform comparisons. All other explanations I've seen that show only numbers oscillating +/-with no waveform comparison were not helped by the verbal misinformation and misinterpretation. Thanks for that! :)
Very, very nice and informative video. I have two chevy Astros throwing the p0420 code. Fixed other codes such as p0300,p1345 and some egr codes. No i have to tackle this p0420.after watching your video i will look at my o2 sensors data and sine wave to determine if my cats are bad. But after watching your video I'm convinced they're bad. Thanks and keep the videos coming!!!!!
Best explanations ever and I have researched and seen so much about this subject...I am sad I have not discovered this website link and its video sooner...many thx. !!!
We look forward to the day that all mechanics are more than just part changers. I love what you do for us. I finally learned what O2 and Cats do. Thanks
+sahmadi1000 Thanks man. I try! Realistically we'll never get everyone to use scientific approach to diagnostic repair but my hope is I can at least be available to everyone like you who WANTS to learn it. There will always be idiots who you can't change. I try to focus on those who want to change and can be changed but they just need a foundation to get information and training.
Thanks for the excellent video. My dealer has just replaced the 2 front O2 sensors due to a P0420 code. This is the 4 time! The cats have already been replaced but about 30K miles ago. This is on a 2005 Subaru LLB H6 engine with only 54000! The CEL is on again and I am taking it back. If they ask me to pay for a cat, I'll scream. I paid $750 for the diagnostic, the 2 sensors and the installation. YIKES!
One of the best videos I've seen that actually EXPLAIN something worth learning about! Only thing I have to say additionally is that not all cars/trucks have sensors both directly before and after the catalytic converter. For example, I have a 1998 Chevy K1500 with a 4.3L V-6 engine. It has 3 oxygen sensors. One in the headpipe off bank one. One in the headpipe off bank 2. The third sensor is after the cat. Nothing more.
That is essentially just exactly the same thing as what's described in the video. It doesn't matter if you have 1 or 2 or 3 or 4 O2 sensors before the car and then O2 sensors after the cat, it is still the same data being read and that is the content of oxygen entering the cat and the content exiting the cat
Thanks for the comments Joenunes. The scantool used at the time of the video was a PC-based one called AutoTap from B&B Electronics which was discontinued some years ago. Recently I upgraded to AutoEnginuity Pro and while it offers much more features, better compatibility with foreign cars, and even some bi-directional capabilities- I still like the software interface of Autotap better and still use it occassionally. But Autoenginuity is the way to go fopr a PC based tool if you're looking.
Many Thanks.... This information has made me see how useless my local mechanic dealership is.... Hats off to you !!! Again many thanks for sharing your knowledge in such helpful way...
It is amazing how many times I had to argue with professional mechanics who would want to replace the rear O2 sensor to fix this code! I guess they make money even when the code does not go away. Thanks for categorically saying that in almost all the cases, you need the converter when you see a waveform like this.
Thanks for the clear explanation. I have a 2005 Nissan Pathfinder with a PO430, I'm pretty sure the cat's just worn out but I'm hoping to check other possibilities before shelling out for a new one.
Thank you for this video. Now I understand a little more about my scanner. My 99 Isuzu Rodeo 4x4 has a P0430 error code as well. Passes every smog test except for the 15mph emissions test. So here's hoping it's the Cat thats causing it.
Very informative and assuring! I watched similar voltage jumps/patterns on a scan tool for my turbo miata... downstream o2 even drops to 0 then comes back online! Going to get it all fixed and tuned! :D
According to this info my cat 2 is shot on my 2k Silverado. Cats are expensive but this info makes since. (Total car diagnostics ELM327 w/ NovaScan) that’s cheap stuff guys but affective. Like $25 I payed. Knowledge is power. Thanks again for your sharing of experience. I am grateful. Anyone throwing rocks needs to produce or get off the crapper btw. Peace all.
@12vgs- Yes, I very often see the O2 diagnosis by professional mechanics too. It is truly one of my biggest peeves and one of the main reason I started doing videos. One trick they use to make money even though the O2's are not responisble for this code is by claiming that "now that the bad O2 was changed , we were also able to diagnose now that the cat is bad as well". Disgusting. This particular code actually confirms the O2’s are working if anything!!!
Excellent explanation! Best on here for this code! I put a plug defouler down stream and seems to be working 5$ vs 400$ customer couldn't afford new cat so I this will work till she can
Huge fan of your videos. While I’m not a scientist, I do approach things scientifically as you do. My question is, although I have (though plan to) not invested or have access to a scan tool yet, I am doing diagnostics with the resources I have currently, but I do have the p0420 code now with no other codes present. I have been using the most basic code reader to diagnose by clearing the code wait for it to set the record freezeframe data from each new drive cycle the code sets. The only consistent factor is that the code only sets in drive, at idle(stoplight), after moderate heavy engine load(highway), after fully warmed up(15+ minutes driving). It never sets under load, cold, or in any other gear, so I suspect there is more at play here. When at idle, before the code sets, I get a strange surging that slightly moves the car, but rpms never fluctuate. No fluid leaks, overheating, or misfire codes, which is what it feels like to me(I suspect it may be so minor and internment that it hasn’t detected it). On freezeframe data, Baro, map, MAF, throttle, temps, all are consistent and check out good, no abnormal reading with multimeter on any ignition components and STFT stays right around 0, and LTFT has moved slightly from -0.8 to +0.8. Where would you advise to go from here? I know I need a scan tool, but any suggestions?
Hi should have watched this before i commented on the trim set of videos. The thing that threw me is on the run live data, the 02 sensors are behaving as expected. Will get a osciliscope to take a closer look. Very informative, thanks.
Yes MainstOrchestra, u do. I get a lot of rebuttals from people claiming exhaust leaks, failing O2 sensors, etc could also cause a P04x0 but the truth is- such conditions are necessarily accounted for in the code. An exhaust leak between the sensors for example would NOT allow a mirror image of the rear and front sensor- the rear sensor would show much leaner than front. An exhaust leak ahead of system would cause mirroring, but the lean front O2 would throw its own code. P04x0= u need a cat.
@@SchrodingersBox I don't know how to test them yet, also, I change the air filter from the engine and appearently that solved the problem. I mean you're the proffesional Im just a DIY I've been watching a lot of videos but it seems really hard to be able to diagnosis properly or there are a lot of possible solutions.
Thank you for your videos, I think that are the most informative, precise AND easy to follow and understand from all of the one on UA-cam. I've had the PO420 on my 2005 Chrysler T&C with 138kmiles just a month ago, this was also accompanied by low power and slow acceleration. The Temperature test on the Cat. did not convince me, maybe I did not do it correctly, but did a vacuum test with the vacuum gauge and that convinced me that it was a clogged Cat. The waveform was almost the same from the two o2s. but at that point I did not know how to read that infos.. because I did not know you and your videos. Anyhow, the cat was clogged, but not only by the carbon built up, but also because it was melted inside. I replaced it and now the car runs....much better. My only concern is that I think it runs a little rich, I see the short fuel trim on the scanner being always - 5 with peaks at -10 and the long term trim baseline at -6, -7 . the MPG is not great neither. The waveform from O2 1 is ok between .2 and .7 and the signal from o2 2 is fairly steady at 0.7, 0.8. Before this video I thought that the downstream signal from the o2 being high would mean a rich condition out of the muffler, Thank you for explaining it is not the case ! I am now on a mission to figure out why it is running a little rich and with a MPG avg. 15miles in city when before it was 18miles. Next to replace would be spark plugs and adding fuel system cleaners Sorry for the long description, cheers...
thank you for reading my comment. replacing the plugs because they are probably due to be replaced at 140kmi.(purchased the van used) Fuel cleaner because I did read somewhere that it could have something to do with fuel filter/pump/regulator , but it is a inexpensive try. The MAF sensor along with trottle body clean and a search for a possible vacuum leak will probably be next. (learned from your videos...) One thing that was interesting to read was that the up.o2 sensor should have been a Mopar and the one installed was not, that makes me worry a little... (By reading your answering, you are one on youtube that replies the most to comments...hats off to you..) TNX !
Fuel cleaner will do nothing, literally pointless. Also being a different brand does not matter as long it is the same type of sensor. Just like there are dozens of brands of oil but 5w30 is 5w30 is 5w30
@GokuBravo-Good question, and it's not as easy as it would seem to detect a bad O2. One giveaway would be an O2 that's "flatlined" but of course that could also be a wiring problem. Another is an O2 that has a normal reading but is very slow to respond to stimulus such as inducing a vacuum leak or adding propane to the intake. But any abnormal O2 traces such as staying rich or lean should not immediately be blamed on the sensor: maybe it is accurately reporting the actual condition!
@schrochem- that's a good one. I'd guess you are due for a P04X0 soon. To get the 04X0 code you cannot simultaneously have other codes which are related to O2 sensors, which you did have with the 0161. Now that the O2's work, my bet is you have freed the CPU up to find "downstream" problems like the cat codes. I would liked to have seen what the O2 waveform was on the S1's that are being mimicked by the S2's- this may explain the .7V at idle but not under load.
Thank you for confirming this! I have a 98 honda dx, p0420 Cel came on, got it diagnos..Thought the mechanic was trying to make some money off me bc i have just replaced my cat in 2009 and now i have to replace it again in 2013.. I even tryd cataclean, was a waste of money..lol thanks again!!!!
Thanks for the explanation. Learning to use my Zurich ZR11 scan tool from Harbor Freight. My 2008 Nissan Titan with 199,700 miles came up with po420 (B1) Changed mass air sensor, both bank 1 O2 sensors, and plugs and coils. Reset computer and got 45 miles before code came back. Looks like my Cat is bad.
Hi, I'd just like to throw something out there, for comment. I own a 2006 Cadillac DTS, w/130K miles. Started getting P0420 codes, a few K miles ago, would set code at between 15-30 miles intervals! Action I took to correct this PROBLEM. #1.Started using " NO ETHENAL " Premium gas .#2.Started using Archoil AR6200, gas treatment . After a few, tanks of gas /Treatment, I stopped setting the P0420 code. Last code set , 300 miles ago ! Cost of gas is high, but worries down! P.S. I also use Archoil AR9100, in engine oil. FYI, I figured this is in the ( general) O2 senser/ catalytic converter area ! I know a lot of worry stopped when it stopped setting the P0420 cade .
Thank you for the video. Excellent information. I've got a 2004 Nissan 3.5L V6 that all of a sudden is displaying both codes. P0420 and P0430. Driveability is "normal". What are the odds that both cats would go bad at once? Does a gasoline formulation change done in this cold weather state of Minnesota twice a year have the potential to cause a code while the fuel supply is transitioning? Could bad injectors or bad plugs cause this? Did not look at live data yet. Thank You.
Amigo Grasias heres un buen Maestro que dios te bendiga amen )))((Hey mate that was a great video with the graphs and your thourogh description very very helpfull.
I was hoping you had a video on this, as I am working on a car for a p0420,0430 problem. I was excited when I saw you had this video listed, and my car is a honda. BUT, figures mine is 2006 and yes, it does have a/f sensors instead-dam it. I thought this was going to be easy. I am guessing you dont have a video on a/f sensors because you said you dont have the scanner?? On my car the rears are 02 sensors though and they are oscilating up and down like your photo and they pretty much dont go over .650 volts. I tried disconnecting the brake booster hose to make lean condition while watching fronts and rears voltage. could not really see much difference though could hear some. Even watch short and long term trim did not tell much?? I am thinking the cats because of how the rear sensors are moving but wish I knew more about how to monitor was is going on with the front sensors. Thanks again for all your GREAT videos!!!
Wonderful video thank you, my 2003 Chevy Impala threw a P0420 code . I ran the sensor voltage graphs and sensor 1 was oscillating as expected and sensor 2 was flat lined at about 770 volts. I guess I’ll have to look elsewhere for the cause. Glad I didn’t buy a CC.
This is very good information. I know it was posted a long time ago, but just now I stumbled into it. I wanted to know if a bad catalytic converter in my 1996 Nissan Altima can cause the MIL to blink randomly as you drive, or is that what everybody tells me is a misfire? My car doesn't show any symptoms of a misfire, there are no codes present and haven't been as long as I have owned the car (since 2000). It drives great. The only issue I had is that I would drive it until it would reach temperature and then I would turn it off. Then after a few minutes it would have a hard time starting. I think that was a fuel issue that I think I repaired since then. I'm afraid to drive the car because of the blinking/flashing MIL. I have some data from my scanner although they are just snapshots of the results. I don't know how to post them here, or if it's possible. Any comments or help would be greatly appreciated. I agree that my vehicle is old, and the catalyst efficiency may have been due to age, but that MIL flashing while I'm driving is my main concern.
@Tommy- You can not have an instance where you have a good cat but S2 copies S1, whether S2 is bad or not. The only exception to this would be if O2 sensor is also bad and has a "flatline" either high or low and S2 copies that flatline. Actually, if anything, a P04x0 actually validates that both sensors are good!
Hello sir, I thoroughly enjoy your videos and have learned an incredible amount from. Unfortunately I have this pesky p0420 code on an in-line 4 cyl. I did replace the cat months ago(because the cat is apart of one solid down pipe which included the flex joint that broke). Not replaced with oem pipe/converter but aftermarket. Got the code shortly after. I do not have access to a scan tool(yet), but do have basic obd2 reader. I always check freeze frame whenever the code pops up. I should mention this code, if I clear it, only returns at idle such as at a stop light after driving for a while. The last time I checked freeze frame I noticed some differences. After engine was fully warmed up, driving at highway speeds for over half an hour, I was back at idle(stoplight to turn into place of work) when code set and fuel system was in open loop. I have always gotten fuel trim data, but this time there was no fuel trim data. Could it be possible this aftermarket cat is no good, or one or both O2 sensors have gone/going bad(both sensors are original with over 200,000 miles on them). I am a very scientific person like you, and do NOT like throwing parts at a car. What would be your next step, assuming no access to live data? Remove sensors and test with multimeter?
I also wanted to know if my vehicle has 2 catalytic converters or just 1. It states it has a precat and then the cat. There's an O2 sensor before the precat at the exhaust manifold and then the exhaust exits the pipe to a straight catalytic converter where after that is a second O2 sensor. So, which one is it, the first or the second, or both? Thanks. My vehicle is a 1996 Nissan Altima.
I'm getting Code P0430 on my truck. I recently changed the Bank 2 Sensor 2 O2 Sensor. My truck doesn't have the most rear sensors ( it does have all four bank 1 & 2 o2 sensors. I'm wondering how I can find out if it's sensor 1 or 2 of bank 2 since it doesn't specifically tell me which. My truck is a 2000 GMC Sierra 1500 5.3L V8 it does not have catalyst converters but yet the code never came up before.
WOW talk about definitive information. I've been kicking around the idea of clearing up my P0420 code with a new converter. Luckily my Torque app has shown an oscillating voltage on my downstream 02 -now you have taught me why. Thank you! Oh, any chance that a converter will create SIGNIFICANTLY more back pressure when it gets really hot? Have a condition (P0420 is the only code) where on the hottest days and after the hot car sits for 30 mins, when driving again it falls on it's face.
Thank very much for your responded. another question, with the stuck lean code. does it affect the engine performance at all or any other fuel trim issue?
@Cooloneoff... Make sure the cat is completely warmed up and also see if you get the "mirroring" sensor readings at 2200RPM which is an even better indicator than Idle. Often dozens of drive cycles can go by before the code returns. A rich LTFT is independent of P0420 UNLESS you have a P0172 (rich code) in which case you shouldnt get P0420 too. If your LTFT is between -12 and -24 I'd do something to fix it as it's bad for your cat to run rich (Even though it won't set P0172 in that range).
The most reasonable explanation I've heard about the o2 sensors, I've watch docens of videos and read articles and none explained it so simply and easy to understand. Great explanation! I believe those wave lengths comparison is at idle, do u know if they should behave the similarly at high rpms? In my cars case the output o2 sensor line goes 'not as flat' does look like there's a bit ot oxigen comming out in high revs, does that mean the cat may be starting to fail? I'd appreciate your input
i have found a rear o2 that had a faulty glitch in the wave pattern on some p420 and 430 codes .i check the temp of the converter .it can tell u to some degree that the converter is working .but i could not see the glitch pattern on a scanner .but i could see on the scope.but like one in a hundred. rare
I am always suspect of the claims of these magic fluids that say you can pour them in your gas tank to work wonders, but do catalytic convertor cleaners actually work? I am about to graph my bank 2 O2 sensors after having a pending P0430 on my 06 Jag Super V8 and since I'm just learning to use the OBDII graphing function on an icarsoft i930, your excellent videos are a big help. Does having a supercharged engine make any difference in the LTFT diagnosis proceedures you present?
For today's cars, both professional and DIY mechanics need to know about what they are working on. The three-way-catalytic converter (TWC) is part of a whole engine fuel/exhaust system design. With a proper functioning engine system, today's TWC are designed to operate for the life of the car and meet emissions requirements. In the case of inefficient TWC, the best way to test is with an exhaust gas analyzer (which are expensive) and proper testing methods of which there are several. If a TWC is determined to be defective, the cause of the failure must first be determined. Not to do effective diagnosis and repair of the root cause of TWC failure can result in replacement failure soon after. For example, California emissions testing is super tough and replacement TWC must meet those requirements. Even replacing a TWC in California must meet strict requirements. In some areas of the U.S. to even replace a TWC requires a special certification. Go to any auto parts web site (try rockauto.com) and notice most of their TWC offerings cannot be sold in California. OEMs are often what is needed. For a comprehensive discussion on engine emissions design and catalytic converter info and testing go to this link. This information is also quite helpful in avoiding a TWC failure in the first place. www.lbcc.edu/attc/documents/BAR-2011-CAT-testing-methods.pdf
Matt, today I used my limited scanner. But I found two things, my long term fuel trim was at 10%, I had two short term fuel trims, B1 and B 2 , but no long term fuel trim was listed for a second bank? Naturally being a neophite, the first thing I will check for is a vacume leak somewhere, the second bank fuel trim would mean either it has none(not likely) or there is a open somewhere since no signal is registering. Please comment. The car is a 1997 Acura CL 3.0, six cylander honda engine.
Excellent video. I am a fan of your fuel trim videos too. My MDX has two banks and thus two catalytic converters. The car started throwing error codes 420 and 430 for both banks. What are the odds both cats have gone bad? The car was running lean for a long time and I finally replaced the plenum gaskets while fixing the broken knock sensor. Both LTFT and STFT are near zero now but the engine light is back on again. Ugh! Appreciate your guidance
I would run the test I showed and trust the results. there is no reason not to expect that both cats can be bad- they are the same age and subjected to same conditions after all.
Low on production value, but really, really high on clear, usable content. Thank you. Was trying to understand the live readings I was getting and this explained it perfectly and clearly. Great video.
You are by far the top internet channel on car diagnostics ! Thank you Sir !
As usual you have done a great job of explaining the root cause. I love your videos and you. I got this code and I just came to your channel and I found my answer. You are a GURU.
Simplified and pretty much to the point ,wish all these types of videos were like this .
This video has been the most informative car video that i have seen in youtube. thanks
I have watched many videos on this site and have done alot of reading regarding auto repair. I just wanted to say thanks for the video. It was very informative and because of the video I was able to gain some knowledge about the diagnosis of these particular diagnostic codes. The video was short and to the point and covered everything that I needed to know. Keep up the good work !
Fantastic video. Easy to follow, great illustrations and clear as to what the cause and solutions are. Thank you VERY much!!!!
It's really nice to have an explanation that is detailed enough to make sense. The code is encompassing at least three different components, as well as a number of issues such as leaks. Being able to look at the signal and understand what it is doing and should be doing is really the only responsible thing to do. Mechanics that either through laziness, lack of proper education and/or greed, can manipulate the test and put the customer through a lot of expense.
I am not a mechanic, but did electronics repairs and felt it was my responsibility to find and repair, for the least expense, the right problem and not just throw a bunch of parts at it and hope one works.
Just wanted to share this guy's issues with this and testing. Because he had issues with various parts, it made the video even more informative.
Hope it adds to this one.
ua-cam.com/video/YL1c-_qLK4Y/v-deo.html
Great video, being an electrical engineer by degree, I immediately understood your explanation using the waveform comparisons. All other explanations I've seen that show only numbers oscillating +/-with no waveform comparison were not helped by the verbal misinformation and misinterpretation. Thanks for that! :)
very nice video with useful information. thank you for doing
the process of diagnosis simple and comprehensible
Thank you, very informative and to the point. I have learned every time I watch your videos.
thanks for that. Very clear and concise explanation. The best video on youtube on p0420!
Very, very nice and informative video. I have two chevy Astros throwing the p0420 code. Fixed other codes such as p0300,p1345 and some egr codes. No i have to tackle this p0420.after watching your video i will look at my o2 sensors data and sine wave to determine if my cats are bad. But after watching your video I'm convinced they're bad. Thanks and keep the videos coming!!!!!
Best explanations ever and I have researched and seen so much about this subject...I am sad I have not discovered this website link and its video sooner...many thx. !!!
We look forward to the day that all mechanics are more than just part changers. I love what you do for us. I finally learned what O2 and Cats do. Thanks
+sahmadi1000 Thanks man. I try! Realistically we'll never get everyone to use scientific approach to diagnostic repair but my hope is I can at least be available to everyone like you who WANTS to learn it. There will always be idiots who you can't change. I try to focus on those who want to change and can be changed but they just need a foundation to get information and training.
Thanks for the excellent video. My dealer has just replaced the 2 front O2 sensors due to a P0420 code. This is the 4 time! The cats have already been replaced but about 30K miles ago. This is on a 2005 Subaru LLB H6 engine with only 54000! The CEL is on again and I am taking it back. If they ask me to pay for a cat, I'll scream. I paid $750 for the diagnostic, the 2 sensors and the installation. YIKES!
Great explanation... very easy to understand. Think I've found my problem thank you!!
great explanation matt now i know why its important to put an oxygen sensor simulators if the cats was removed thank you for the great videos .
One of the best videos I've seen that actually EXPLAIN something worth learning about! Only thing I have to say additionally is that not all cars/trucks have sensors both directly before and after the catalytic converter. For example, I have a 1998 Chevy K1500 with a 4.3L V-6 engine. It has 3 oxygen sensors. One in the headpipe off bank one. One in the headpipe off bank 2. The third sensor is after the cat. Nothing more.
That is essentially just exactly the same thing as what's described in the video. It doesn't matter if you have 1 or 2 or 3 or 4 O2 sensors before the car and then O2 sensors after the cat, it is still the same data being read and that is the content of oxygen entering the cat and the content exiting the cat
Thanks for the comments Joenunes. The scantool used at the time of the video was a PC-based one called AutoTap from B&B Electronics which was discontinued some years ago. Recently I upgraded to AutoEnginuity Pro and while it offers much more features, better compatibility with foreign cars, and even some bi-directional capabilities- I still like the software interface of Autotap better and still use it occassionally. But Autoenginuity is the way to go fopr a PC based tool if you're looking.
Schrodingers Box Hello there where do you find that Scan Tool? And what does it go for? Thanks
Many Thanks.... This information has made me see how useless my local mechanic dealership is.... Hats off to you !!! Again many thanks for sharing your knowledge in such helpful way...
+Christopher Kelly Hahaha well creating disdain for your local mechanic wasn't the intent but I have found it to be a corollary to me creations.
Great vid to understand the diffrence between clogged and low efficient catalytic converter thanks man
REALLY GOOD VIDEO!! very clear explanation!! I read a lot about it but I couldn't really understand the problem. Now I know thanks to you.
It is amazing how many times I had to argue with professional mechanics who would want to replace the rear O2 sensor to fix this code! I guess they make money even when the code does not go away. Thanks for categorically saying that in almost all the cases, you need the converter when you see a waveform like this.
outstanding! this is perhaps the CLEAREST instruction......... thank you!
Not even a leak in the exhaust will cause the same input and output. That is a strong statement. I like it.
Very helpful. Thanks! Makes all kinds of sense. Thanks for bringing the concept out into the open and so clear to understand.
You're very welcome!
Thank you very much, I’ve been wanting to learn about this for a long time
Great info, this saved me from a lot of time waste and unnecessary changing of parts
How did you fix it?
@@gibson7654 My issue was a blocked exhaust
@@skodbolle How did you fix it?
Thanks a lot, I feel way more confident testing my CAT now
thank you, this video helps clarify what exactly is the culprit, for code P0420
Muchas Gracias por la pasiencia y la grandesa DE Como esplicas el video DE grand ayuda alos mecanicos avan empesando bye papi
Thanks for the clear explanation. I have a 2005 Nissan Pathfinder with a PO430, I'm pretty sure the cat's just worn out but I'm hoping to check other possibilities before shelling out for a new one.
Thank you for all your videos Matt, I personally appreciate
My pleasure!
Thank you for this video. Now I understand a little more about my scanner. My 99 Isuzu Rodeo 4x4 has a P0430 error code as well. Passes every smog test except for the 15mph emissions test. So here's hoping it's the Cat thats causing it.
makes complete sense, well explained. thanks for posting
Really well worded explanation. Much appreciated.
Very well done. Simple, direct and effective. Thanks
Such a fantastic explanation!!! Thank you.👍👍👍
Sir you are God sent...
I owe u a lot.
Gee, spoke before actually checking, I do see you have some info on the a/f sensors so I am looking forward to viewing it NOW, thanks.
Very informative and assuring!
I watched similar voltage jumps/patterns on a scan tool for my turbo miata... downstream o2 even drops to 0 then comes back online! Going to get it all fixed and tuned! :D
This confirms that I don't need replaces sensors or buy snake oil, thanks for not let me waste my money and save it for a cat replacement.
Really appreciate you sir.Great job.love your efforts
According to this info my cat 2 is shot on my 2k Silverado. Cats are expensive but this info makes since. (Total car diagnostics ELM327 w/ NovaScan) that’s cheap stuff guys but affective. Like $25 I payed. Knowledge is power.
Thanks again for your sharing of experience. I am grateful. Anyone throwing rocks needs to produce or get off the crapper btw.
Peace all.
@12vgs- Yes, I very often see the O2 diagnosis by professional mechanics too. It is truly one of my biggest peeves and one of the main reason I started doing videos. One trick they use to make money even though the O2's are not responisble for this code is by claiming that "now that the bad O2 was changed , we were also able to diagnose now that the cat is bad as well". Disgusting. This particular code actually confirms the O2’s are working if anything!!!
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Hi. The graph you showed at the end. What was the RPM.
Excellent explanation! Best on here for this code! I put a plug defouler down stream and seems to be working 5$ vs 400$ customer couldn't afford new cat so I this will work till she can
So when you put the defouler on, what was the trace on the O2S2 so you know it actually worked?
Huge fan of your videos. While I’m not a scientist, I do approach things scientifically as you do. My question is, although I have (though plan to) not invested or have access to a scan tool yet, I am doing diagnostics with the resources I have currently, but I do have the p0420 code now with no other codes present. I have been using the most basic code reader to diagnose by clearing the code wait for it to set the record freezeframe data from each new drive cycle the code sets. The only consistent factor is that the code only sets in drive, at idle(stoplight), after moderate heavy engine load(highway), after fully warmed up(15+ minutes driving). It never sets under load, cold, or in any other gear, so I suspect there is more at play here. When at idle, before the code sets, I get a strange surging that slightly moves the car, but rpms never fluctuate. No fluid leaks, overheating, or misfire codes, which is what it feels like to me(I suspect it may be so minor and internment that it hasn’t detected it). On freezeframe data, Baro, map, MAF, throttle, temps, all are consistent and check out good, no abnormal reading with multimeter on any ignition components and STFT stays right around 0, and LTFT has moved slightly from -0.8 to +0.8. Where would you advise to go from here? I know I need a scan tool, but any suggestions?
You can't tell anything from that data. You need to look for superimposition of the S1 and S2 voltages. All else is irrelevant.
Hi should have watched this before i commented on the trim set of videos. The thing that threw me is on the run live data, the 02 sensors are behaving as expected. Will get a osciliscope to take a closer look. Very informative, thanks.
Hey mate that was a great video with the graphs and your thourogh description very very helpfull.
Pretty good presentation, keep up the good work!
Very Good video. Now I know how how catalytic converter works.
Thanks for the video. Once again a great explanation.
Yes MainstOrchestra, u do. I get a lot of rebuttals from people claiming exhaust leaks, failing O2 sensors, etc could also cause a P04x0 but the truth is- such conditions are necessarily accounted for in the code. An exhaust leak between the sensors for example would NOT allow a mirror image of the rear and front sensor- the rear sensor would show much leaner than front. An exhaust leak ahead of system would cause mirroring, but the lean front O2 would throw its own code. P04x0= u need a cat.
Good evening Mr. I have a question I had P0420 and P0430 I replaced the spark plugs and the code is gone now. Why was that possible?
@@mtsanchez27 it’s not. what does your S2 output voltage show?
@@SchrodingersBox I don't know how to test them yet, also, I change the air filter from the engine and appearently that solved the problem. I mean you're the proffesional Im just a DIY I've been watching a lot of videos but it seems really hard to be able to diagnosis properly or there are a lot of possible solutions.
Thank you for your videos, I think that are the most informative, precise AND easy to follow and understand from all of the one on UA-cam.
I've had the PO420 on my 2005 Chrysler T&C with 138kmiles just a month ago, this was also accompanied by low power and slow acceleration.
The Temperature test on the Cat. did not convince me, maybe I did not do it correctly, but did a vacuum test with the vacuum gauge and that convinced me that it was a clogged Cat. The waveform was almost the same from the two o2s. but at that point I did not know how to read that infos.. because I did not know you and your videos.
Anyhow, the cat was clogged, but not only by the carbon built up, but also because it was melted inside.
I replaced it and now the car runs....much better. My only concern is that I think it runs a little rich, I see the short fuel trim on the scanner being always - 5 with peaks at -10 and the long term trim baseline at -6, -7 . the MPG is not great neither.
The waveform from O2 1 is ok between .2 and .7 and the signal from o2 2 is fairly steady at 0.7, 0.8.
Before this video I thought that the downstream signal from the o2 being high would mean a rich condition out of the muffler, Thank you for explaining it is not the case !
I am now on a mission to figure out why it is running a little rich and with a MPG avg. 15miles in city when before it was 18miles.
Next to replace would be spark plugs and adding fuel system cleaners
Sorry for the long description, cheers...
I have no idea why you conclude to use fuel system cleaners and replace plugs. What am I missing??
thank you for reading my comment.
replacing the plugs because they are probably due to be replaced at 140kmi.(purchased the van used)
Fuel cleaner because I did read somewhere that it could have something to do with fuel filter/pump/regulator , but it is a inexpensive try. The MAF sensor along with trottle body clean and a search for a possible vacuum leak will probably be next. (learned from your videos...)
One thing that was interesting to read was that the up.o2 sensor should have been a Mopar and the one installed was not, that makes me worry a little...
(By reading your answering, you are one on youtube that replies the most to comments...hats off to you..)
TNX !
Fuel cleaner will do nothing, literally pointless. Also being a different brand does not matter as long it is the same type of sensor. Just like there are dozens of brands of oil but 5w30 is 5w30 is 5w30
Awesome explanation, now I understand
This should really help!
Thank you.
God bless!!!
Schrodingers Box you explained it very well. Thanks for sharing.
Thanks!!
Great video. Thank you for the lesson.
@GokuBravo-Good question, and it's not as easy as it would seem to detect a bad O2. One giveaway would be an O2 that's "flatlined" but of course that could also be a wiring problem. Another is an O2 that has a normal reading but is very slow to respond to stimulus such as inducing a vacuum leak or adding propane to the intake. But any abnormal O2 traces such as staying rich or lean should not immediately be blamed on the sensor: maybe it is accurately reporting the actual condition!
@schrochem- that's a good one. I'd guess you are due for a P04X0 soon. To get the 04X0 code you cannot simultaneously have other codes which are related to O2 sensors, which you did have with the 0161. Now that the O2's work, my bet is you have freed the CPU up to find "downstream" problems like the cat codes. I would liked to have seen what the O2 waveform was on the S1's that are being mimicked by the S2's- this may explain the .7V at idle but not under load.
Thank you for confirming this! I have a 98 honda dx, p0420 Cel came on, got it diagnos..Thought the mechanic was trying to make some money off me bc i have just replaced my cat in 2009 and now i have to replace it again in 2013.. I even tryd cataclean, was a waste of money..lol
thanks again!!!!
Amazing explanation in just few minutes. 😁
Thank you very much for your video. I learned a lot!
Super helpful! Great video!
Thanks for the explanation. Learning to use my Zurich ZR11 scan tool from Harbor Freight.
My 2008 Nissan Titan with 199,700 miles came up with po420 (B1)
Changed mass air sensor, both bank 1 O2 sensors, and plugs and coils. Reset computer and got 45 miles before code came back. Looks like my Cat is bad.
Hi, I'd just like to throw something out there, for comment. I own a 2006 Cadillac DTS, w/130K miles. Started getting P0420 codes, a few K miles ago, would set code at between 15-30 miles intervals! Action I took to correct this PROBLEM. #1.Started using " NO ETHENAL " Premium gas .#2.Started using Archoil AR6200, gas treatment . After a few, tanks of gas /Treatment, I stopped setting the P0420 code. Last code set , 300 miles ago ! Cost of gas is high, but worries down! P.S. I also use Archoil AR9100, in engine oil. FYI, I figured this is in the ( general) O2 senser/ catalytic converter area ! I know a lot of worry stopped when it stopped setting the P0420 cade .
Ok.... where is your data showing you reversed superimposition of the S2 signal??
Very informative. Great job.
Thanks for a clear explanation of things.
Thanks a million your vids are the best
Very helpful Video. thanks for your time.
Thanks for the awesome video. Very informative,
Amazing O2 live data lecturing!
Outstanding education!!
Thank you for the video. Excellent information. I've got a 2004 Nissan 3.5L V6 that all of a sudden is displaying both codes. P0420 and P0430. Driveability is "normal". What are the odds that both cats would go bad at once? Does a gasoline formulation change done in this cold weather state of Minnesota twice a year have the potential to cause a code while the fuel supply is transitioning? Could bad injectors or bad plugs cause this? Did not look at live data yet. Thank You.
I'm having this problem right thank you for the great info
Amigo Grasias heres un buen Maestro que dios te bendiga amen )))((Hey mate that was a great video with the graphs and your thourogh description very very helpfull.
I was hoping you had a video on this, as I am working on a car for a p0420,0430 problem. I was excited when I saw you had this video listed, and my car is a honda. BUT, figures mine is 2006 and yes, it does have a/f sensors instead-dam it. I thought this was going to be easy. I am guessing you dont have a video on a/f sensors because you said you dont have the scanner?? On my car the rears are 02 sensors though and they are oscilating up and down like your photo and they pretty much dont go over .650 volts. I tried disconnecting the brake booster hose to make lean condition while watching fronts and rears voltage. could not really see much difference though could hear some. Even watch short and long term trim did not tell much?? I am thinking the cats because of how the rear sensors are moving but wish I knew more about how to monitor was is going on with the front sensors. Thanks again for all your GREAT videos!!!
Wonderful video thank you, my 2003 Chevy Impala threw a P0420 code . I ran the sensor voltage graphs and sensor 1 was oscillating as expected and sensor 2 was flat lined at about 770 volts. I guess I’ll have to look elsewhere for the cause. Glad I didn’t buy a CC.
be sure to check it at 2500 rpm though. it might show the issue then.
@@SchrodingersBox it’s still flatlining but at 100 volts at 2500 rpm’s huh
This is very good information. I know it was posted a long time ago, but just now I stumbled into it. I wanted to know if a bad catalytic converter in my 1996 Nissan Altima can cause the MIL to blink randomly as you drive, or is that what everybody tells me is a misfire? My car doesn't show any symptoms of a misfire, there are no codes present and haven't been as long as I have owned the car (since 2000). It drives great. The only issue I had is that I would drive it until it would reach temperature and then I would turn it off. Then after a few minutes it would have a hard time starting. I think that was a fuel issue that I think I repaired since then. I'm afraid to drive the car because of the blinking/flashing MIL. I have some data from my scanner although they are just snapshots of the results. I don't know how to post them here, or if it's possible. Any comments or help would be greatly appreciated. I agree that my vehicle is old, and the catalyst efficiency may have been due to age, but that MIL flashing while I'm driving is my main concern.
It is a very useful video, thank you so much
@Tommy- You can not have an instance where you have a good cat but S2 copies S1, whether S2 is bad or not. The only exception to this would be if O2 sensor is also bad and has a "flatline" either high or low and S2 copies that flatline. Actually, if anything, a P04x0 actually validates that both sensors are good!
Hello sir, I thoroughly enjoy your videos and have learned an incredible amount from. Unfortunately I have this pesky p0420 code on an in-line 4 cyl. I did replace the cat months ago(because the cat is apart of one solid down pipe which included the flex joint that broke). Not replaced with oem pipe/converter but aftermarket. Got the code shortly after. I do not have access to a scan tool(yet), but do have basic obd2 reader. I always check freeze frame whenever the code pops up. I should mention this code, if I clear it, only returns at idle such as at a stop light after driving for a while. The last time I checked freeze frame I noticed some differences. After engine was fully warmed up, driving at highway speeds for over half an hour, I was back at idle(stoplight to turn into place of work) when code set and fuel system was in open loop. I have always gotten fuel trim data, but this time there was no fuel trim data. Could it be possible this aftermarket cat is no good, or one or both O2 sensors have gone/going bad(both sensors are original with over 200,000 miles on them). I am a very scientific person like you, and do NOT like throwing parts at a car. What would be your next step, assuming no access to live data? Remove sensors and test with multimeter?
Excellent! explanation. Thank you very much.
I also wanted to know if my vehicle has 2 catalytic converters or just 1. It states it has a precat and then the cat. There's an O2 sensor before the precat at the exhaust manifold and then the exhaust exits the pipe to a straight catalytic converter where after that is a second O2 sensor. So, which one is it, the first or the second, or both? Thanks. My vehicle is a 1996 Nissan Altima.
very good video,and we'll explained as always, thank you
Everardo Camacho q
I'm getting Code P0430 on my truck. I recently changed the Bank 2 Sensor 2 O2 Sensor. My truck doesn't have the most rear sensors ( it does have all four bank 1 & 2 o2 sensors. I'm wondering how I can find out if it's sensor 1 or 2 of bank 2 since it doesn't specifically tell me which.
My truck is a 2000 GMC Sierra 1500 5.3L V8 it does not have catalyst converters but yet the code never came up before.
WOW talk about definitive information. I've been kicking around the idea of clearing up my P0420 code with a new converter. Luckily my Torque app has shown an oscillating voltage on my downstream 02 -now you have taught me why. Thank you! Oh, any chance that a converter will create SIGNIFICANTLY more back pressure when it gets really hot? Have a condition (P0420 is the only code) where on the hottest days and after the hot car sits for 30 mins, when driving again it falls on it's face.
Thank very much for your responded. another question, with the stuck lean code. does it affect the engine performance at all or any other fuel trim issue?
A lean code will affect engine performance if the LTFT is unable to maintain stoic on the O2s. Otherwise there will be no symptoms or ill effects.
@Cooloneoff... Make sure the cat is completely warmed up and also see if you get the "mirroring" sensor readings at 2200RPM which is an even better indicator than Idle. Often dozens of drive cycles can go by before the code returns. A rich LTFT is independent of P0420 UNLESS you have a P0172 (rich code) in which case you shouldnt get P0420 too. If your LTFT is between -12 and -24 I'd do something to fix it as it's bad for your cat to run rich (Even though it won't set P0172 in that range).
The most reasonable explanation I've heard about the o2 sensors, I've watch docens of videos and read articles and none explained it so simply and easy to understand. Great explanation! I believe those wave lengths comparison is at idle, do u know if they should behave the similarly at high rpms? In my cars case the output o2 sensor line goes 'not as flat' does look like there's a bit ot oxigen comming out in high revs, does that mean the cat may be starting to fail? I'd appreciate your input
Actually the numbers should be read at 2200 RPM however a really strong cat will show these at idle.
Great teacher!
Well explained,thank you
i have found a rear o2 that had a faulty glitch in the wave pattern on some p420 and 430 codes .i check the temp of the converter .it can tell u to some degree that the converter is working .but i could not see the glitch pattern on a scanner .but i could see on the scope.but like one in a hundred. rare
I am always suspect of the claims of these magic fluids that say you can pour them in your gas tank to work wonders, but do catalytic convertor cleaners actually work? I am about to graph my bank 2 O2 sensors after having a pending P0430 on my 06 Jag Super V8 and since I'm just learning to use the OBDII graphing function on an icarsoft i930, your excellent videos are a big help. Does having a supercharged engine make any difference in the LTFT diagnosis proceedures you present?
At what conditions should I be reading an accurate wave signal. What if you have a straight line at a lower voltage 250mv on second sensor.?
For today's cars, both professional and DIY mechanics need to know about what they are working on. The three-way-catalytic converter (TWC) is part of a whole engine fuel/exhaust system design. With a proper functioning engine system, today's TWC are designed to operate for the life of the car and meet emissions requirements. In the case of inefficient TWC, the best way to test is with an exhaust gas analyzer (which are expensive) and proper testing methods of which there are several. If a TWC is determined to be defective, the cause of the failure must first be determined. Not to do effective diagnosis and repair of the root cause of TWC failure can result in replacement failure soon after. For example, California emissions testing is super tough and replacement TWC must meet those requirements. Even replacing a TWC in California must meet strict requirements. In some areas of the U.S. to even replace a TWC requires a special certification. Go to any auto parts web site (try rockauto.com) and notice most of their TWC offerings cannot be sold in California. OEMs are often what is needed. For a comprehensive discussion on engine emissions design and catalytic converter info and testing go to this link. This information is also quite helpful in avoiding a TWC failure in the first place. www.lbcc.edu/attc/documents/BAR-2011-CAT-testing-methods.pdf
Great Job!!!!!!!!!!!!!!!!! Thank you!!!!!!!!!!!!!!!!!!
Matt, today I used my limited scanner. But I found two things, my long term fuel trim was at 10%, I had two short term fuel trims, B1 and B 2 , but no long term fuel trim was listed for a second bank? Naturally being a neophite, the first thing I will check for is a vacume leak somewhere, the second bank fuel trim would mean either it has none(not likely) or there is a open somewhere since no signal is registering. Please comment. The car is a 1997 Acura CL 3.0, six cylander honda engine.
Excellent video. I am a fan of your fuel trim videos too. My MDX has two banks and thus two catalytic converters. The car started throwing error codes 420 and 430 for both banks. What are the odds both cats have gone bad? The car was running lean for a long time and I finally replaced the plenum gaskets while fixing the broken knock sensor. Both LTFT and STFT are near zero now but the engine light is back on again. Ugh! Appreciate your guidance
I would run the test I showed and trust the results. there is no reason not to expect that both cats can be bad- they are the same age and subjected to same conditions after all.