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.
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. ruclips.net/video/YL1c-_qLK4Y/видео.html
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 !
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! :)
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 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.
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 .
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.
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.
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. !!!
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!
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!!!!!
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.
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
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...
@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!!!
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.
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.
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?
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.
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
@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!
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!!!!
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 RUclips. 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
@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.
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.
@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!
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
@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).
You're welcome Rebel... one observation however. If you had to change the cat after not even 4 years, I might suspect your engine could be running rich (but not enough to set a code or A) your CEL would have come on sooner and B) you can't get a P0420 with a simultaneous rich/lean code). You might want to keep that in mind- a rich condition will kill a cat much sooner because the temperature will increase dramatically. Also, it's likely your cat has a longer warranty that 3 or 4 years too.
If you don't mind me asking, what do you do for a living? I'm professional L 1 ASE and you're self learned? I've had automotive instructors that didn't explain diag theory as well as you do.
+689452379 Thanks man! I am a scientist for a living. I often have to explain scientific concepts to lay-people which is probably where the teaching ability comes in. Thanks for the compliment!
Schrodingers Box No wonder why you are so intellectual... I’m totally a visual guy Question what scan tool are you using with the graphs and oscillating
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
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
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.
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 had a 98 Mazda 626 throw a cat code. Didn't have 70k miles on it. It was leaking oil into the one spark plug well. It never threw a code for a miss but it would miss now and then. I replaced the valve cover gaskets. No more cat codes for at least two years (I sold the car)
Ah, Chris, an idle mind is the devil's playground but an evil mind is his kingdom. Indeed your clever idea to bypass the cat has come across many a similarly wicked mind but it has also come across the engineers' minds as well. The problem is the constant 900V signal appearing at warmup while the cat is not working at the engine runs rich will throw a B2 sensor code on most models. Models with AIR also use the O2 sensor as indicator the system is working. Codes other than 0420 would result.
Schrodingers Box so would a peak detection circuit using the S1 waveform work as an S2 signal then? Or did the engineers put more stringent requirements in their screens?
I believe an exhaust leak can also simulate a failed catalytic converter. It's a good idea to pressure test your exhaust system. Or, like Ericthecarguy, do it old school (I think he does more of the old school just to help the DIY who has less stuff. :) ) and put get a rag strapped to the back of your muffler and look for leaks that have become more obvious. I think it's helpful to to literally run your hand around your exhaust tubes while in operation. You don't have to touch it, just have it close so you can feel the air or heat escaping in certain spots. In my case, the springs were bad between the manifold and my down pipe. The engine has to be able to twist a little on start up or during revving, and this is where on my car there is a donut on top of the downpipe to twist and keep a seal. Have a bad spring and when the engine twists you'll have a leak. I had to really think about it to figure this out, it's hard to rev an engine and have your hands in there, lol. Lucky me, 1 of the 2 springs were too badly rusted in, but 1 was enough to stop the leak. I'm sure, I'll have to get the other eventually, but great penetrating spray sometimes isn't enough, you need an acetylene torch. I don't have one yet, lol. Note I also had a bad catalytic converter, but the code may not have cleared do to the leak.
An exhaust leak can indeed be a downstream O2 sensor problem, but it will not cause a "mirroring" of the front O2 coding a 04x0 code. No combination of exhaust leaks will cause the rear O2 to have an oscillation pattern matching that of a front O2. Good point about the shadetree techniques- my channel tends not to focus on those but one common shadetree technique to validate the O2 sensor is to use a temperature sensor gun to monitor exhaust pipe temp before and after the cat. I'm not sure what the parameters are that one would look for but I would assume you want a hotter post-cat temp than pre-cat. If the temps are the same, no cat activity is assumed.
The other issue I still have after the new cat is the downstream staying close to 100 milivolts. I thought this was supposed to happen from this being my only cat replacement experience...but your video is showing the opposite. . . I have something to unlearn?
Yes I have sometimes seen this as well and i'm not sure why the sensor sometimes seems stuck lean like that but if you test it at 2500RPM it should definitely show rich (technically, I should say it should show to have high voltage). I have also seen some cars where for whatever reason you don't get o2 sensor response unless the vehicle is actually driving. In either case, I am not sure what the programming/mechanics are behind that- I never looked into it. I don't recall the make exactly, but I recently worked on a car where the O2s were flatlined unless the car was actually driving.
I'll be breaking out of it's brand new packaging a laser thermometer. Take it for a drive. Keep it above 2500 RPM and reading the front and back temperature. Maybe this will give me another clue.
Hi Matt. Thanks so much for the video. However, my car has an AF sensor precat and a regular O2 sensor post cat. Could you explain what you expect to see on their graph tracings for this situation if you have a GOOD cat vs a BAD cat? Thanks again; phenomenal channel.
It will be the same trace on the S2 (post cat) as shown in the video. Remember your AF sensor is technically still oscillating (as evidenced by the STFT) so you will see that reflected in the S2 if there is no catalytic activity.
hey nice video thanks for sharing. I have a 2001 Saab 9-5 and to day cleaned my throtttle body. While testing the car, the check engine light came on with a P0420 code. This was performed at the local auto parts store. The slip they gave me had the following written on it: Catalyst efficiency low-bank, The oxygen sensors monitor the catalytic converters ability to store oxygen. Probable cause; catalytic converter defective (failure possible due to #2,3, or 4); Engine misfire or running condition; large vacuum leak; Engine oil leakage into exhaust-value guide seals piston rings. Based on your great video how do you thing I can determine which of these codes I should move forward with first? I look forward to your reply.
Thanks good stuff my sensor 1 bank 1 is going up and down between 3.24 volts and 3.69 volts my sensor 2 bank 1 is steady at 0.855 volts I hope I'm out of the danger zone will appreciate the feedback, also my car is a lexus 2008 V8 since you mentioned toyota Thanks
What do you recommend as the car is running good except for check engine light i was going to pull out a/f to see condition so my reading is pointless? Not sure don want to replace cat just yet but its my daily
@@SchrodingersBox hello thanks unfortunately your talking a foreign language to me lol I will try and replacing the both sensors on bank 1 or least try and cleaning them and see what happens I always use premium gas and occasionally throw in a seafoam in tank I guess I will take to shop because I don't know how to test like you say thanks for the response
THANKS THIS IS VERY HELPFUL ONE QUESTION IF I HAVE UPSTREAM CONVERTERS AND DOWNSTREAM CONVERTERS SHOULD I CHANGE BOTH OR JUST THE DOWN STREAM CONVERTER WORKING ON 2005NISSAN FRONTER 4.0L V6 HAS CODE PO420 TW CATALYST SYS B-1 WHAT DOES TW MEAN AFTER PO420? THANKS YOU ARE A GOOD TEACHER
While the advice in this video will work most of the time, in that mirrored HO2S signals are a red flag that a cat is non-functional, there are times that replacing the cat for a P0420 code will not fix the problem. The PCM is normally very good at determining if the cat needs replaced, however, a few things can fool it into falsely displaying this code. What needs to be verified before going with a P0420/P0430 cat replacement is that: 1) The car is in good control of the fuel. Your trims need to be centered around stoich. 2) There are no exhaust leaks present. Exhaust leaks between the manifold and the cat can cause the PCM to flag a cat, falsely. 3) No TSB's or reflashes have been released that deal with this problem on your vehicle. 4) The sensors, up stream and down stream, are functioning and responding properly. A faulty sensor - especially upstream sensor - can cause the PCM to falsely flag a cat as failing. BTDT, have the scars to prove it. If these four items are verified to be okay, then believe the PCM and replace the catalytic converter. Part of the misconception stems from the name of the sensor - oxygen sensor. It actually doesn't sense O2 as much as it senses O2 demand. That is why Robert Bosch called it a Lambda Sensor when he invented it. GM took the ball and ran with it, calling it an oxygen sensor in their early training manuals ... and it stuck. Truth is, if you place a zirconia sensor in oxygen, it'll flat line, meaning no activity. But if you screw it into a tube filled with HC, it'll peg. It gets excited in the presence of combustibles. HTH
1. Please explain how a fuel trim issue would possibly be a factor. You CAN NOT have a P04X0 code AND a P017X code simultaneously. It is impossibl;e. 2. How could an exhaust leak cause mirroring effect? It may cause a lean effect- sure (which I disproved in a A/F sensor video) but even if it did, it could not cause mirroring. Further it would cause a P017X code and see #1. 3. Correct. And reflashes are not fixes anyway. computers don't suddenly "lose" their programming. Flashes are done by people who couldn't identify the etiology. 4. Again you cannot get an O2 sensor code AND a cat code. If the o2 sensors are not working you will get an O2 related code. You need to show EXAMPLES or LOGICAL EXPLANATIONS to the contrary. For example, describe a hypothetical situation where a LTFT at 25 as a result of an exhaust leak could result in a P0420 rather and P0171.
Remember, the point I was making is that a PCM can, on occasion, store a P0420/P0430, when the cat actually hasn't failed, if some issues exist. Having seen and experienced these situations, I shared what I have observed. Now to your comments and questions: 1) I did not say that the two codes would exist simultaneously. In fact, I cannot imagine a scenario where that could happen. What I have seen is that if fuel trims are skewed, then the PCM can have a marginal base line to begin its calculations, and the result can cause other codes to be set, such as HO2S codes, or catalyst codes. The point is that if you have a vehicle that is not in good control of the fuel mixture, then you really can't trust the codes being reported until fuel trims are brought back into line. 2) I did not say that exhaust leaks cause a mirroring effect. Similar to the answer in #1, an exhaust leak can cause a miscalculation by the PCM, resulting in a code being set that is not the actual issue. In this case, an exhaust leak introduces false air, which can bias the HO2S voltage (or amperage - depending on sensor style), causing a problem with the calculations. 3) Flashing is done to update the software - not because the PCM "lost" its programming. The manufacturers release software updates periodically and inform technicians through TSB's or, in more severe cases, they will issue a recall. 4) Again, I did not say that you would see both codes simultaneously. I have seen a P0420 set in a vehicle that had a brand new, completely functional catalyst. The front HO2S was operating, but the amplitude of the sine wave was off by about 0.2v (0.1v on each end of the scale). The rear HO2S was mirroring the front, and actually had a slightly larger amplitude than the front HO2S. In this case, replacing the front HO2S solved the problem. Early on, mirroring was something that the PCM relied on heavily, to determine catalyst functionality. More recently, most strategies have shifted to a measured response time during an enrichment/lean cycle, since that is a more accurate method of determining oxygen storage capacity. I am not disagreeing with you about mirroring being a a red flag, and a good indicator that a cat is likely failing. I am saying that anyone suspecting a cat failure should verify the four conditions that I listed, and if they all check out okay, then go ahead and replace the converter. It is possible to have mirroring with a good cat, in some situations. Since this is an expensive part, take the necessary steps to eliminate any other potential causes, and then proceed with the replacement of the cat, if warranted. HTH
You still failed to example a mechanism for an example where what you say would be true. Here- example- Exhaust leak- HOW would you get a P0420 from that. Again I gave explanation on why you would not. You would get a decreased voltage on O2S from the leak and thus either lean code or O2 OOR code due to the decreased O2 vo0ltage. PLEASE give the mechanism for how this would result in a Cat code rather than O2 lean code.
And u hear your cat rumbling and you cant get over 35MPH BUT I still need to diagnose the root cause of what killed my catalytic converter. Gracias maestro! Im screenshooting and writing notes. I have my FSM but can’t make sense of the books.
The newer cars use wideband oxygen sensors, not A/F sensors. Both types of sensors only measure oxygen content and infer mixture from it. The difference is that narrowband sensors are only accurate in a small window around a 14.7:1 mixture and wideband sensors are calibrated over a much larger range. Since these sensors (both NB and WB) only detect oxygen and not mixture, they can't distinguish between a lean mixture and a misfire since both conditions result in large quantities of oxygen in the exhaust stream.
Schrodingers Box The point was don't fool yourself into thinking that the wideband sensors actually measure the mixture. They are still oxygen sensors and can be fooled by engine misfires.
ollopa1 A/F's measure the mixture allright. How do you otherwise explain the reversal in polarity with amperage variance directly proportional to the stoichiometric conditions?
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 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!!!
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.
I've seen some people automatically condemn the converter because they see the downstream signal exactly following the upstream signal. However, the upstream signal wasn't cycling correctly to begin with. It would seem that if you have a bad upstream signal you need to fix that first. My understanding is that the converter won't do its job properly if the mixture going into the cat isn't cycling properly. So if you were to replace the cat the new one won't work correctly either because the exhaust mixture going into the new cat still won't be cycling correctly.
+Joe Vignolo If the upsteam is not cycling properly and the front O2 has a code, it precludes any codes for the cat. Even so- if the front sensor is not operating, the cat HAS to still make a change by default because of the chemical activity. You cannot turn off catalytic activity.
+Schrodingers Box - If the upstream O2 sensor is cycling correctly voltage-wise but is cycling too slowly frequency-wise you may not get any codes associated directly with the upstream O2 sensor, there will be no drivability issues or plug carbonization, the fuel trims will look fine and the system will run closed loop. But the slow cycling can cause the converter efficiency to drop below the threshold and trip a P0420 or PO430 code. So if you have a slow upstream sensor you need to fix that problem first before condemning the converter. Remember that later model cars do not use auxiliary air pumps to oxygenate the converters or electric heaters to heat them up. Instead, they use the engine itself to do it. That's what the cycling is for. The lean part of the cycle pumps in the extra oxygen that the converter stores up to use later. The rich part of the cycle pumps in extra HC, which the converter burns to generate the heat it needs to operate correctly. So if the cycling is happening too slow, the catalytic activity will drop off and you will get a PO420 or PO430 code. I suspect that a lot of perfectly good catalytic converters are ending up in the scrap pile because people are not diagnosing these situations properly. You need to fix any abnormal conditions that are inhibiting the converter before you replace the converter.
Joe Vignolo Explain the chemistry of how the catalytic converter would suddenly have low efficiency as result of slow upstream cycling. That makes no sense to me whatsoever. The catalytic activity is constant, not variable.
+Schrodingers Box - It's somewhat complicated, but basically it has to do with oxygen storage inside the converter. Modern three way catalytic converters (TWCs) that do not use external air injection have cerium in them. Cerium absorbs oxygen, stores it and then releases it. But cerium has its limitations. It will only absorb small amounts of oxygen and it can only release as much oxygen as it has previously absorbed. Cerium allows the catalyst to operate efficiently under slightly rich and slightly lean conditions only for very short time periods. So if the air/fuel mixture is continuously cycled from slightly rich to slightly lean fast enough, cerium can allow the converter to constantly operate at maximum efficiency. But if the cycling frequency drops too low this little trick will no longer work. This is because the pulses of oxygen contained in the cycle are too long and too far apart. Therefore, during the excessively long, lean parts of the cycle the cerium absorbs only as much oxygen as it can until it saturates and can't absorb any more. This means that the amount of oxygen that the cerium in the converter can store is limited. This then means that during the excessively long, rich parts of the cycle the cerium doesn't have a sufficient amount of oxygen stored up to properly oxygenate the converter all the way through to the next new lean cycle. This in turn causes the converter to become under-oxygenated during the rich parts of the cycle, which in turn causes its efficiency to drop.
***** In that event however you would not MIRROR proper O2 waveform. Yes there are actually many, many instances where you could have lean or rich conditions affecting trace from the cat but only one possibility where you mirror proper waveform from the front sensor.
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.
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.
This video has been the most informative car video that i have seen in youtube. thanks
Simplified and pretty much to the point ,wish all these types of videos were like this .
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.
ruclips.net/video/YL1c-_qLK4Y/видео.html
Not even a leak in the exhaust will cause the same input and output. That is a strong statement. I like it.
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 !
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! :)
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.
Fantastic video. Easy to follow, great illustrations and clear as to what the cause and solutions are. Thank you VERY much!!!!
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
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??
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.
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.
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.
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.
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. !!!
very nice video with useful information. thank you for doing
the process of diagnosis simple and comprehensible
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!
Thank you, very informative and to the point. I have learned every time I watch your videos.
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!!!!!
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.
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
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 explanation... very easy to understand. Think I've found my problem thank you!!
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?
@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.
thanks for that. Very clear and concise explanation. The best video on youtube on p0420!
Thank you very much, I’ve been wanting to learn about this for a long time
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.
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.
Muchas Gracias por la pasiencia y la grandesa DE Como esplicas el video DE grand ayuda alos mecanicos avan empesando bye papi
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.
Amazing O2 live data lecturing!
Thanks a lot, I feel way more confident testing my CAT now
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.
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.
outstanding! this is perhaps the CLEAREST instruction......... 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 .
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!
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?
Such a fantastic explanation!!! Thank you.👍👍👍
Really well worded explanation. Much appreciated.
thank you, this video helps clarify what exactly is the culprit, for code P0420
@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!
Thank you for all your videos Matt, I personally appreciate
My pleasure!
makes complete sense, well explained. thanks for posting
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 for your videos, I think that are the most informative, precise AND easy to follow and understand from all of the one on RUclips.
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
Sir you are God sent...
I owe u a lot.
@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.
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.
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
@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!
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
Great vid to understand the diffrence between clogged and low efficient catalytic converter thanks man
Schrodingers Box you explained it very well. Thanks for sharing.
Thanks!!
@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).
Very well done. Simple, direct and effective. Thanks
Hey mate that was a great video with the graphs and your thourogh description very very helpfull.
You're welcome Rebel... one observation however. If you had to change the cat after not even 4 years, I might suspect your engine could be running rich (but not enough to set a code or A) your CEL would have come on sooner and B) you can't get a P0420 with a simultaneous rich/lean code). You might want to keep that in mind- a rich condition will kill a cat much sooner because the temperature will increase dramatically. Also, it's likely your cat has a longer warranty that 3 or 4 years too.
Awesome explanation, now I understand
Pretty good presentation, keep up the good work!
Very informative. Great job.
Very Good video. Now I know how how catalytic converter works.
Really appreciate you sir.Great job.love your efforts
Good explanation at all.
Thanks for a clear explanation of things.
If you don't mind me asking, what do you do for a living? I'm professional L 1 ASE and you're self learned? I've had automotive instructors that didn't explain diag theory as well as you do.
+689452379 Thanks man! I am a scientist for a living. I often have to explain scientific concepts to lay-people which is probably where the teaching ability comes in. Thanks for the compliment!
Schrodingers Box
No wonder why you are so intellectual... I’m totally a visual guy Question what scan tool are you using with the graphs and oscillating
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
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.
Outstanding education!!
It is a very useful video, thank you so much
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.
Finally somebody who knows what they talking about.
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.
Thanks for the video. Once again a great explanation.
I had a 98 Mazda 626 throw a cat code. Didn't have 70k miles on it. It was leaking oil into the one spark plug well. It never threw a code for a miss but it would miss now and then. I replaced the valve cover gaskets. No more cat codes for at least two years (I sold the car)
and what was the downstream O2 sensor voltage showing?
Ah, Chris, an idle mind is the devil's playground but an evil mind is his kingdom. Indeed your clever idea to bypass the cat has come across many a similarly wicked mind but it has also come across the engineers' minds as well. The problem is the constant 900V signal appearing at warmup while the cat is not working at the engine runs rich will throw a B2 sensor code on most models. Models with AIR also use the O2 sensor as indicator the system is working. Codes other than 0420 would result.
Schrodingers Box
so would a peak detection circuit using the S1 waveform work as an S2 signal then? Or did the engineers put more stringent requirements in their screens?
I believe an exhaust leak can also simulate a failed catalytic converter. It's a good idea to pressure test your exhaust system. Or, like Ericthecarguy, do it old school (I think he does more of the old school just to help the DIY who has less stuff. :) ) and put get a rag strapped to the back of your muffler and look for leaks that have become more obvious.
I think it's helpful to to literally run your hand around your exhaust tubes while in operation. You don't have to touch it, just have it close so you can feel the air or heat escaping in certain spots.
In my case, the springs were bad between the manifold and my down pipe. The engine has to be able to twist a little on start up or during revving, and this is where on my car there is a donut on top of the downpipe to twist and keep a seal. Have a bad spring and when the engine twists you'll have a leak.
I had to really think about it to figure this out, it's hard to rev an engine and have your hands in there, lol. Lucky me, 1 of the 2 springs were too badly rusted in, but 1 was enough to stop the leak. I'm sure, I'll have to get the other eventually, but great penetrating spray sometimes isn't enough, you need an acetylene torch. I don't have one yet, lol.
Note I also had a bad catalytic converter, but the code may not have cleared do to the leak.
An exhaust leak can indeed be a downstream O2 sensor problem, but it will not cause a "mirroring" of the front O2 coding a 04x0 code. No combination of exhaust leaks will cause the rear O2 to have an oscillation pattern matching that of a front O2.
Good point about the shadetree techniques- my channel tends not to focus on those but one common shadetree technique to validate the O2 sensor is to use a temperature sensor gun to monitor exhaust pipe temp before and after the cat. I'm not sure what the parameters are that one would look for but I would assume you want a hotter post-cat temp than pre-cat. If the temps are the same, no cat activity is assumed.
About 100 degrees hotter on the back of the cat I heard from Eric?
The other issue I still have after the new cat is the downstream staying close to 100 milivolts. I thought this was supposed to happen from this being my only cat replacement experience...but your video is showing the opposite. . . I have something to unlearn?
Yes I have sometimes seen this as well and i'm not sure why the sensor sometimes seems stuck lean like that but if you test it at 2500RPM it should definitely show rich (technically, I should say it should show to have high voltage). I have also seen some cars where for whatever reason you don't get o2 sensor response unless the vehicle is actually driving. In either case, I am not sure what the programming/mechanics are behind that- I never looked into it. I don't recall the make exactly, but I recently worked on a car where the O2s were flatlined unless the car was actually driving.
I'll be breaking out of it's brand new packaging a laser thermometer. Take it for a drive. Keep it above 2500 RPM and reading the front and back temperature. Maybe this will give me another clue.
Thanks a million your vids are the best
Hi Matt. Thanks so much for the video. However, my car has an AF sensor precat and a regular O2 sensor post cat. Could you explain what you expect to see on their graph tracings for this situation if you have a GOOD cat vs a BAD cat? Thanks again; phenomenal channel.
It will be the same trace on the S2 (post cat) as shown in the video. Remember your AF sensor is technically still oscillating (as evidenced by the STFT) so you will see that reflected in the S2 if there is no catalytic activity.
hey nice video thanks for sharing. I have a 2001 Saab 9-5 and to day cleaned my throtttle body. While testing the car, the check engine light came on with a P0420 code. This was performed at the local auto parts store. The slip they gave me had the following written on it: Catalyst efficiency low-bank, The oxygen sensors monitor the catalytic converters ability to store oxygen. Probable cause; catalytic converter defective (failure possible due to #2,3, or 4); Engine misfire or running condition; large vacuum leak; Engine oil leakage into exhaust-value guide seals piston rings. Based on your great video how do you thing I can determine which of these codes I should move forward with first? I look forward to your reply.
I would look at the O2 sensor data for pre and post cat and determine if there is evidence of lack of cat activity.
Thanks good stuff my sensor 1 bank 1 is going up and down between 3.24 volts and 3.69 volts my sensor 2 bank 1 is steady at 0.855 volts I hope I'm out of the danger zone will appreciate the feedback, also my car is a lexus 2008 V8 since you mentioned toyota Thanks
you have an A/F sensor, not a O2 sensor.
What do you recommend as the car is running good except for check engine light i was going to pull out a/f to see condition so my reading is pointless? Not sure don want to replace cat just yet but its my daily
on an AF sensor you need to read it by equivalence ratio, not voltage. the voltage number is just an arbitrary absolute value.
@@SchrodingersBox hello thanks unfortunately your talking a foreign language to me lol I will try and replacing the both sensors on bank 1 or least try and cleaning them and see what happens I always use premium gas and occasionally throw in a seafoam in tank I guess I will take to shop because I don't know how to test like you say thanks for the response
Excellent! explanation. Thank you very much.
THANKS THIS IS VERY HELPFUL ONE QUESTION IF I HAVE UPSTREAM CONVERTERS AND DOWNSTREAM CONVERTERS SHOULD I CHANGE BOTH OR JUST THE DOWN STREAM CONVERTER WORKING ON 2005NISSAN FRONTER 4.0L V6 HAS CODE PO420 TW CATALYST SYS B-1 WHAT DOES TW MEAN AFTER PO420? THANKS YOU ARE A GOOD TEACHER
While the advice in this video will work most of the time, in that mirrored HO2S signals are a red flag that a cat is non-functional, there are times that replacing the cat for a P0420 code will not fix the problem. The PCM is normally very good at determining if the cat needs replaced, however, a few things can fool it into falsely displaying this code. What needs to be verified before going with a P0420/P0430 cat replacement is that:
1) The car is in good control of the fuel. Your trims need to be centered around stoich.
2) There are no exhaust leaks present. Exhaust leaks between the manifold and the cat can cause the PCM to flag a cat, falsely.
3) No TSB's or reflashes have been released that deal with this problem on your vehicle.
4) The sensors, up stream and down stream, are functioning and responding properly. A faulty sensor - especially upstream sensor - can cause the PCM to falsely flag a cat as failing. BTDT, have the scars to prove it.
If these four items are verified to be okay, then believe the PCM and replace the catalytic converter.
Part of the misconception stems from the name of the sensor - oxygen sensor. It actually doesn't sense O2 as much as it senses O2 demand. That is why Robert Bosch called it a Lambda Sensor when he invented it. GM took the ball and ran with it, calling it an oxygen sensor in their early training manuals ... and it stuck. Truth is, if you place a zirconia sensor in oxygen, it'll flat line, meaning no activity. But if you screw it into a tube filled with HC, it'll peg. It gets excited in the presence of combustibles.
HTH
1. Please explain how a fuel trim issue would possibly be a factor. You CAN NOT have a P04X0 code AND a P017X code simultaneously. It is impossibl;e.
2. How could an exhaust leak cause mirroring effect? It may cause a lean effect- sure (which I disproved in a A/F sensor video) but even if it did, it could not cause mirroring. Further it would cause a P017X code and see #1.
3. Correct. And reflashes are not fixes anyway. computers don't suddenly "lose" their programming. Flashes are done by people who couldn't identify the etiology.
4. Again you cannot get an O2 sensor code AND a cat code. If the o2 sensors are not working you will get an O2 related code.
You need to show EXAMPLES or LOGICAL EXPLANATIONS to the contrary. For example, describe a hypothetical situation where a LTFT at 25 as a result of an exhaust leak could result in a P0420 rather and P0171.
Remember, the point I was making is that a PCM can, on occasion, store a P0420/P0430, when the cat actually hasn't failed, if some issues exist. Having seen and experienced these situations, I shared what I have observed. Now to your comments and questions:
1) I did not say that the two codes would exist simultaneously. In fact, I cannot imagine a scenario where that could happen. What I have seen is that if fuel trims are skewed, then the PCM can have a marginal base line to begin its calculations, and the result can cause other codes to be set, such as HO2S codes, or catalyst codes. The point is that if you have a vehicle that is not in good control of the fuel mixture, then you really can't trust the codes being reported until fuel trims are brought back into line.
2) I did not say that exhaust leaks cause a mirroring effect. Similar to the answer in #1, an exhaust leak can cause a miscalculation by the PCM, resulting in a code being set that is not the actual issue. In this case, an exhaust leak introduces false air, which can bias the HO2S voltage (or amperage - depending on sensor style), causing a problem with the calculations.
3) Flashing is done to update the software - not because the PCM "lost" its programming. The manufacturers release software updates periodically and inform technicians through TSB's or, in more severe cases, they will issue a recall.
4) Again, I did not say that you would see both codes simultaneously. I have seen a P0420 set in a vehicle that had a brand new, completely functional catalyst. The front HO2S was operating, but the amplitude of the sine wave was off by about 0.2v (0.1v on each end of the scale). The rear HO2S was mirroring the front, and actually had a slightly larger amplitude than the front HO2S. In this case, replacing the front HO2S solved the problem.
Early on, mirroring was something that the PCM relied on heavily, to determine catalyst functionality. More recently, most strategies have shifted to a measured response time during an enrichment/lean cycle, since that is a more accurate method of determining oxygen storage capacity.
I am not disagreeing with you about mirroring being a a red flag, and a good indicator that a cat is likely failing. I am saying that anyone suspecting a cat failure should verify the four conditions that I listed, and if they all check out okay, then go ahead and replace the converter.
It is possible to have mirroring with a good cat, in some situations. Since this is an expensive part, take the necessary steps to eliminate any other potential causes, and then proceed with the replacement of the cat, if warranted.
HTH
You still failed to example a mechanism for an example where what you say would be true.
Here- example- Exhaust leak- HOW would you get a P0420 from that. Again I gave explanation on why you would not. You would get a decreased voltage on O2S from the leak and thus either lean code or O2 OOR code due to the decreased O2 vo0ltage.
PLEASE give the mechanism for how this would result in a Cat code rather than O2 lean code.
I'm having this problem right thank you for the great info
And u hear your cat rumbling and you cant get over 35MPH BUT I still need to diagnose the root cause of what killed my catalytic converter. Gracias maestro! Im screenshooting and writing notes. I have my FSM but can’t make sense of the books.
The newer cars use wideband oxygen sensors, not A/F sensors. Both types of sensors only measure oxygen content and infer mixture from it. The difference is that narrowband sensors are only accurate in a small window around a 14.7:1 mixture and wideband sensors are calibrated over a much larger range. Since these sensors (both NB and WB) only detect oxygen and not mixture, they can't distinguish between a lean mixture and a misfire since both conditions result in large quantities of oxygen in the exhaust stream.
The post cats are still zirconia dioxide though
Schrodingers Box
The point was don't fool yourself into thinking that the wideband sensors actually measure the mixture. They are still oxygen sensors and can be fooled by engine misfires.
ollopa1 A/F's measure the mixture allright. How do you otherwise explain the reversal in polarity with amperage variance directly proportional to the stoichiometric conditions?
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 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!!!
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.
Great video. Thank you for the lesson.
I've seen some people automatically condemn the converter because they see the downstream signal exactly following the upstream signal. However, the upstream signal wasn't cycling correctly to begin with.
It would seem that if you have a bad upstream signal you need to fix that first. My understanding is that the converter won't do its job properly if the mixture going into the cat isn't cycling properly. So if you were to replace the cat the new one won't work correctly either because the exhaust mixture going into the new cat still won't be cycling correctly.
+Joe Vignolo If the upsteam is not cycling properly and the front O2 has a code, it precludes any codes for the cat.
Even so- if the front sensor is not operating, the cat HAS to still make a change by default because of the chemical activity. You cannot turn off catalytic activity.
+Schrodingers Box - If the upstream O2 sensor is cycling correctly voltage-wise but is cycling too slowly frequency-wise you may not get any codes associated directly with the upstream O2 sensor, there will be no drivability issues or plug carbonization, the fuel trims will look fine and the system will run closed loop. But the slow cycling can cause the converter efficiency to drop below the threshold and trip a P0420 or PO430 code. So if you have a slow upstream sensor you need to fix that problem first before condemning the converter.
Remember that later model cars do not use auxiliary air pumps to oxygenate the converters or electric heaters to heat them up. Instead, they use the engine itself to do it. That's what the cycling is for. The lean part of the cycle pumps in the extra oxygen that the converter stores up to use later. The rich part of the cycle pumps in extra HC, which the converter burns to generate the heat it needs to operate correctly. So if the cycling is happening too slow, the catalytic activity will drop off and you will get a PO420 or PO430 code.
I suspect that a lot of perfectly good catalytic converters are ending up in the scrap pile because people are not diagnosing these situations properly. You need to fix any abnormal conditions that are inhibiting the converter before you replace the converter.
Joe Vignolo Explain the chemistry of how the catalytic converter would suddenly have low efficiency as result of slow upstream cycling. That makes no sense to me whatsoever. The catalytic activity is constant, not variable.
+Schrodingers Box - It's somewhat complicated, but basically it has to do with oxygen storage inside the converter. Modern three way catalytic converters (TWCs) that do not use external air injection have cerium in them. Cerium absorbs oxygen, stores it and then releases it. But cerium has its limitations. It will only absorb small amounts of oxygen and it can only release as much oxygen as it has previously absorbed. Cerium allows the catalyst to operate efficiently under slightly rich and slightly lean conditions only for very short time periods. So if the air/fuel mixture is continuously cycled from slightly rich to slightly lean fast enough, cerium can allow the converter to constantly operate at maximum efficiency. But if the cycling frequency drops too low this little trick will no longer work. This is because the pulses of oxygen contained in the cycle are too long and too far apart. Therefore, during the excessively long, lean parts of the cycle the cerium absorbs only as much oxygen as it can until it saturates and can't absorb any more. This means that the amount of oxygen that the cerium in the converter can store is limited. This then means that during the excessively long, rich parts of the cycle the cerium doesn't have a sufficient amount of oxygen stored up to properly oxygenate the converter all the way through to the next new lean cycle. This in turn causes the converter to become under-oxygenated during the rich parts of the cycle, which in turn causes its efficiency to drop.
***** In that event however you would not MIRROR proper O2 waveform. Yes there are actually many, many instances where you could have lean or rich conditions affecting trace from the cat but only one possibility where you mirror proper waveform from the front sensor.
Very helpful Video. thanks for your time.
Thank you very much for your video. I learned a lot!
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.