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 !

This video has been the most informative car video that i have seen in youtube. thanks

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 .

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!!!!

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.

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.

@Wakeupandsniffthecoffee

4 жыл бұрын

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. kzread.info/dash/bejne/i4BlxY-Yoa-xZLw.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! :)

thanks for that. Very clear and concise explanation. The best video on youtube on p0420!

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

@SchrodingersBox

8 жыл бұрын

+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!!

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. !!!

Not even a leak in the exhaust will cause the same input and output. That is a strong statement. I like it.

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.

outstanding! this is perhaps the CLEAREST instruction......... thank 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.

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.

@Mr.Thermistor7228

5 ай бұрын

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

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 .

Great vid to understand the diffrence between clogged and low efficient catalytic converter thanks man

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...

@SchrodingersBox

8 жыл бұрын

+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.

Thanks a lot, I feel way more confident testing my CAT now

makes complete sense, well explained. thanks for posting

Thank you very much, I’ve been wanting to learn about this for a long time

Really well worded explanation. Much appreciated.

Such a fantastic explanation!!! Thank you.👍👍👍

Muchas Gracias por la pasiencia y la grandesa DE Como esplicas el video DE grand ayuda alos mecanicos avan empesando bye papi

Very well done. Simple, direct and effective. Thanks

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.

@jamesbarlowjr.3762

4 жыл бұрын

Schrodingers Box Hello there where do you find that Scan Tool? And what does it go for? Thanks

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.

Great info, this saved me from a lot of time waste and unnecessary changing of parts

@gibson7654

3 жыл бұрын

How did you fix it?

@skodbolle

3 жыл бұрын

@@gibson7654 My issue was a blocked exhaust

@gibson7654

3 жыл бұрын

@@skodbolle How did you fix it?

Very helpful. Thanks! Makes all kinds of sense. Thanks for bringing the concept out into the open and so clear to understand.

@SchrodingersBox

Жыл бұрын

You're very welcome!

thank you, this video helps clarify what exactly is the culprit, for code P0420

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

Thank you for all your videos Matt, I personally appreciate

@SchrodingersBox

Жыл бұрын

My pleasure!

Sir you are God sent... I owe u a lot.

Awesome explanation, now I understand

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.

Amazing O2 live data lecturing!

Pretty good presentation, keep up the good work!

Great video. Thank you for the lesson.

Really appreciate you sir.Great job.love your efforts

Thanks for the video. Once again a great explanation.

Very Good video. Now I know how how catalytic converter works.

Very informative. Great job.

Hey mate that was a great video with the graphs and your thourogh description very very helpfull.

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.

Super helpful! Great video!

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. 😁

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.

This should really help! Thank you. God bless!!!

Outstanding education!!

Thanks for a clear explanation of things.

Thank you very much for your video. I learned a lot!

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

@SchrodingersBox

4 жыл бұрын

So when you put the defouler on, what was the trace on the O2S2 so you know it actually worked?

Schrodingers Box you explained it very well. Thanks for sharing.

@SchrodingersBox

6 жыл бұрын

Thanks!!

Thanks for the awesome video. Very informative,

Thanks a million your vids are the best

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.

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 helpful Video. thanks for your time.

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

Great teacher!

It is a very useful video, thank you so much

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 .

@SchrodingersBox

5 жыл бұрын

Ok.... where is your data showing you reversed superimposition of the S2 signal??

Well explained,thank you

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.

What an amazing video.

Excellent! explanation. Thank you very much.

@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.

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?

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.

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?

@SchrodingersBox

5 жыл бұрын

You can't tell anything from that data. You need to look for superimposition of the S1 and S2 voltages. All else is irrelevant.

EXCELLANT VID, THANKS FOR POSTING!!!!!

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.

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 KZread. 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...

@SchrodingersBox

7 жыл бұрын

I have no idea why you conclude to use fuel system cleaners and replace plugs. What am I missing??

@babies6951

7 жыл бұрын

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 !

@Mr.Thermistor7228

5 ай бұрын

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

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?

Great Job!!!!!!!!!!!!!!!!! Thank you!!!!!!!!!!!!!!!!!!

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.

outstanding bro thanks !!

@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!

I cleaned my MAF today and tried to follow your example to check the pending P0430 on my 06 Jaguar Super V8 with an icarsoft i930 scanner. The choices for O2 sensor 1 are either current or lambda (my UltraGage says "wide O2 Lambda") and not voltage so I assume the fore cat O2 sensors on the Jag are of a different type than the after cat sensors. Is there a proceedure for checking catalyst efficiency with this type of sensor? I also get way out of range spikes on the i930 graphs and the scale expands to cover the max and min values so the lower value traces between spikes are impossible to read accurately. I'd guess you don't have that problem with your scantool.

very good video,and we'll explained as always, thank you

@dennisbochmann3820

7 жыл бұрын

Everardo Camacho q

@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!!!

@jred2b

3 жыл бұрын

Qq1aaaaaaaaaaaaaàaaaaàaaaaaaaaaaaaaaaaaaaaaaàaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaàaaaa

@pacman7959

3 жыл бұрын

Hi. The graph you showed at the end. What was the RPM.

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!!!

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.

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?

@SchrodingersBox

7 жыл бұрын

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.

Good explanation at all.

thank you for this nice video

also mat i have a chevorlet aveo it also has p0420, i just remove the heat shield and found that the manifold was cracked, so i tried to weld it back did a decent job. after a week the problem came back, this time when i checked i noticed that as soon as i hit the throttle the downstream o2 sensor voltage fluctuates, so what do you say maybe i still have a leak and also this car has a exhaust leak after downstream o2 sensor, can this be an issue?

Hi there. This a perfect video! I'm new to scanner use but had a p0161 (bank 2,sensor2). I have 168K and never replaced the sensors so I went ahead and did all 4 based on the graphs I was getting. I know bank1,sensor 1 wasn't oscilating very well. After replacement, I ran the graph again. At idle sensors 2 hold at about 0.7V but at 2500rpm they start mimicking sensors 1. Why? Based on your video I see the cats are bad but not at idle. Does cataclean work? No sulfur smell. Idles very smooth. thx

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.?

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.

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.

@mtsanchez27

3 жыл бұрын

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?

@SchrodingersBox

3 жыл бұрын

@@mtsanchez27 it’s not. what does your S2 output voltage show?

@mtsanchez27

3 жыл бұрын

@@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.