Diagnosing a catalyst efficiency code (P0420 or P0430)

[@mhiggins3460]

Finally, someone who knows what the hell they’re talking about. This video is a true diamond in the rough. So much BS associated with the P0420 code. Thanks a ton for taking the time to make a quality, informed video

[@ScannerDanner]

Thanks so much!

[@micahrobles5210]

Seriously. This video clears up so much of the mystery in regards to Cat inefficiency DTCs. It makes sense now why the spark plug extensions hack works to temporarily trick the ECM into thinking the cat is fine. Pulling the sensor out of the stream and reducing the amount of gas it's exposed to emulates the lower O2 value the ECM is expecting. Note to nerds like ScannerDanner, be sure to tell the hillbilly why it works so we can limit the amount of backwoods magic they push. JK... Nice content!

[@johnharbour633]

​@@ScannerDannernew to the concept of scopes... possible explain how you choose to connect leads?

[@ScannerDanner]

@@johnharbour633 a lap scope is nothing more than a very fast voltmeter, you would connect a scope to get a signal the exact way you would connect a voltmeter to get a signal. One lead to the wire you are testing and the other lead to battery ground

[@davidkeyes2435]

@@ScannerDanner I really need you me help telling me if this means when it jumps (usually) is it clogged or just failing?? Like if it is still flowing it has no effect on performance so it doesn’t mTter to me but if it’s clogged that is performance issues???

[@twistedimaginationballoons9641]

I've watched alot videos the last few days, working to making sure the cat is my issue. Even bought an "entry" level scan tool. This is by the far the best explained and informative video I've found. Thanks for helping a handy guy like me, play mechanic when I have to. 🙄

[@ronaldmahoney1283]

You are an expert in teaching theology step by step so that anyone could fully understand the concepts of automotive to do most any repair given the aptitude of the individual! I totally commend you for that! Thank You!

[@ScannerDanner]

Thank you Ronald

[@NIS_ONE]

Well I ran into this today. Wife's car throwing a p0420 (2011 Nissan Altima S 2.5) Checked for leaks, checked sensors, checked fuel trims, and honestly I was a little lost. Then I got and idea💡 search for some scanner danner p0420 trouble shooting videos, came across this one which just stepped my game up when it comes to confirming a bad cat. Ran a propane enrichment test BINGO bad cat. Man I love these videos. Before I can say and admit I was a parts changer but now I have learned the error of my ways watching many MANY of these videos by Mr. Danner. Thanks again for all the great you do my good sir!

[@ScannerDanner]

Thanks so much!

[@mike-yp1uk]

I absolutely appreciate your dedication to create better technicians. It's time to sign up and get saturated by all your material again. It really makes all the difference. I made major strides in my career as a result of using this advanced training.

[@ScannerDanner]

Thank you Mike! Looking forward to hearing from you in the comments section of the classes

[@SaltyTubers]

Six and half years later, still relevant and helpful! Thank you @ScannerDanner!

[@steadyeddie7453]

One difference now is that many upstream sensors are air fuel rato (AF) sensors which produce different graph readings. So comparing waveforms from an upstream sensor to a downstream sensor doesnt work. The point being be sure if you are dealing with an upstream O2 or AF sensor. The emissions sticker under the hood will tell you.

[@3rdbass618]

Excellent Sir! I bought my 2006 Chrysler 300 in 2005. Check engine light came on within a month. It ran rough for a while and eventually started back running like a sewing machine, as it does today, still. The light stayed on though. I kept procasting and failed to take it back to dealer for repair while under warranty. When you said a converter can be bad while a car runs smooth, it made perfect sense, especially since the reputable car repair shop replaced OEM oxygen sensors after the p0240 code came up, showing they needed replaced. The light is back on after 53 miles with the same stored (not active code) I am now convinced that the converter is bad and will by one from the dealer and have it installed. I hope this will take of the problem once and for all.

[@2secondslater]

Been binge watching your videos again. We had huge problems here in Oz with the Holden Commodore (US Pontiac GTO I think), with the early LS series engines throwing P0420 and P0430 codes, GM Holden must have made hundreds of thousands of dollars, if not millions on replacement convertors, which, came with replacement exhaust flange gaskets. After the first two or three I saw with the fault I decided to do a bit more testing, smoke tested the exhaust, with engine not running, no leaks, smoke tested the engine whilst turning it over by hand, exhaust pipes plugged, no leaks. Finally flooded the engine running with the smoke tester, with UV dye added to the smoke oil. I discovered UV dye staining around the donut style flange gaskets, the leak would only occur with the engine running, the problem was the gaskets would go hard with age and then leak when engine vibration was a factor. GM Holden made a massive amount of money selling new convertors when the fix really was the new gaskets that came with the new convertors. After the initial testing we made hundreds of fixes to customer's vehicles by replacing gaskets only. Moral of the story... test, don't guess.

[@DanWallis86]

Hey Jake. Great write up. I’m in Australia too and see these codes quite often. Very interesting. Where in Australia are you?

[@2secondslater]

@@DanWallis86 Perth mate

[@DanWallis86]

Me too. Are you on Facebook? Can I send you a message on there?

[@2secondslater]

@@DanWallis86 not on FB.

[@DanWallis86]

@@2secondslater no worries. I like your write up you did on the exhaust leak. Thinking outside the box a bit. I’m in a few mechanic groups on Facebook and a mate of mine has a shop in gnangara. We have been trying to organise a couple of training nights for local mechanics to learn about pulse sensors and scope use. Would be good to get people who like to take a somewhat different approach to repairs rather than just firing the parts cannon.

[@ozzstars_cars]

Ughhh the dreaded P0420. My wifes 2001 Subaru Outback, 3.0L six cylinder, 190K miles started to throw this code now and again for several months. Well tuned engine, no exhaust or intake leaks. Engine was running good. I removed and thoroughly cleaned the inside of the original PVC valve and added a high quality fuel injection cleaner in the gas tank. I cleared the code. It has been 6 months now, NO problem. Most 420 codes do mean a cat replacement is necessary but not always. Great video!

[@thereckchanic4709]

Well said, I would do the same especially after checking for any leaks on the intake and exhaust. Sometime just cleaning the sensor or replacing it will do the truck. I’ve heard of many guys replacing the Cats and still had the same results.

[@Leroyjenkinsjnr]

Awesome video. I've got a vehicle coming in this afternoon. An MOT station has told him his car has only just passed emissions and he needs a cat. I cannot wait to test it now! Thankyou

[@JBAutomotive794]

Paul, I can't tell you how many times I've learned something from your videos over the many years ive been watching. Thank you so much for taking the time to make these videos. These are priceless for new techs showing them the theory of how modern vehicles work. Cheers brother 🍻

[@ScannerDanner]

Thanks man. Some of the material is timeless and is just as relevant today. Appreciate your comments

[@desiefiautoelectrician7150]

There is a lot to learn in each of your videos. You are a good person. You share your experience with us.

[@sizzlacalunji]

This is gold. I have been struggling with my accord and trying to understand these things and this made it so easy. Will download that ebook. That’s a price to pay to learn and understand what’s going on vs spending hundreds to a mechanic who will do trial and error and still have the code...

[@ScannerDanner]

Trial and error certainly is not the troubleshooting I teach. Thank you very much!

[@_valles3438]

Thank you for the graphics showing the results of both the good and bad catalytic converter oxygen sensor readings!!

[@U.B.A_AutoDiag]

@ScannerDanner this is exactly how a study videos supposed to be.i am only beginner and your channel is a store of knowledge i follow, watching and studying. please, accept my appreciation for a job you doing here. thank you and best of luck.🤝

[@ScannerDanner]

Thank you! This is an example of one of hundreds of classes i offer just like this on my website www.scannerdanner.com/join-scannerdanner-premium.html Hope to see you there!

[@U.B.A_AutoDiag]

@@ScannerDanner I would love to.. But before that have to finish to watch all your videos here )))) Cheers

[@ScannerDanner]

@@U.B.A_AutoDiag for sure! And we have over 900 videos here on KZbin and over 600 on my website. I mentioned the website because it contains ALL of my classroom lectures (like this one), where here on KZbin I've only sampled from them from time to time. Anyway, no matter where you watch, I appreciate the support!

[@UnknownMexicanMuslim]

Any other UTI Technician learning more from this channel than the classes ever taught 😂

[@klmachineandwelding4834]

Fantastic video. Helped me tremendously to diagnose a P0420 code to make certain that the converter was actually bad. Thanks for a really informative video.

[@NavyGirlO6]

Thanks, Paul! Fantastic education on what we can look at to understand cat status. Diagnostics over parts cannon. Because of this vid I found ForScan available for my ‘05 Ford Escape 3.0L, and well worth the price of a dedicated OBDII connector with Ethernet cable. I can now evaluate these same values and graphs, which has alleviated my concern about the front two cats (had to replace the rear, which crapped out not long after repairing the famous Ford Escape ignition coil problem causing misfires). So much more confident in monitoring things myself now.

[@blueocean9305]

You’re no parts chaser. Well explained and thoughtful. Thanks.

[@user-up3xc1np4g]

I have a 2001 taurus it was throwing the PO420 code as well, plus gas mileage was down. Changed all 4 O2 sensors. Dumped a bottle of cat cleaning solution in it at 1/4 tank drove like 45 minutes. Cleared codes. And the PO420 code popped back up. Got online and googled the PO420 codes it said check O2 sensors which I replaced all 4, check ECS (engine coolant sensor) sensor. I scanned it it was running at 174 going highway speed until I slowed down then it would go up to 185-190. So I decided to change the ECS sensor to see what it would do after clearing the codes again. And the PO420 code hasn't popped up since then and the temp has been at 185-190 since and my gas mileage went back up too. And it's been a week since changing the ECS sensor. So I'm guessing it was ECS all along with the PO420 code and not the cat's or the O2 sensors. Thank god I didn't replace my cat's w/o changing my ECS sensor first. I do cheap parts first b4 going to the most expensive parts. Sorry for the long story lol.

[@scottykilmer3920]

i had a car with a p0420 code diagnosing. It wasnt the cat or oxygen sensors, but the problem was a faulty intermittent crankshaft sensor !

[@alanmatthews5949]

Wished you did bonus footage of the propane test after repair.

[@Dark_Knight_USA]

Greetings: Use VIN tag not other tags...true. Sometimes there is a midyear production change. Use the later designation. Good show. Thx 4 the share.

[@spoke2soon]

Extremely thorough, and I am grateful for it! Thank you for enriching my troubleshooting tactics.

[@BlueEyeTableRockLake]

Great info, My friends 2011 Arcadia has po420&30 codes still with all new o2s and cats. When I heard it wasn't fixed I scanned the SUV and found the downstream o2s almost mirror the upstream sensors. He said they put in OEM parts.??? Now I've got some direction to go after S & L trims all looked good. It runs great and no other values out of range. O2s all respond correctly to rich lean commands. I'll check common components to both banks like PVC, leaks intake or exhaust, and them run the o2 retention test. Thanks! Oh forgot GM TSB PIP5232A states check engine block grounds on vehicles 2015 and older if you have cat failures. I find that interesting.

[@ScannerDanner]

Did they use OEM cats? I doubt it as they're 3 or 4 times the cost of aftermarket. Unfortunately that is what is needed on these! Factory cats only!

[@TheR35nismo]

very informative video, love the content, successfully help me to determine which o2 sensor was failing on my car and also help me save some money, thanks mate

[@joshuagibson2520]

Thanks man. Most valuable video there is on the topic. Wish I'd watched it first. The shorter vids I watched taught me just enough to be dangerous. You really went over a lot of variables that are important. Thorough as can be. Thanks again.

[@ScannerDanner]

Thank you!

[@confidential8738]

Wish i lived in PA. I could probably pass ur class jus from the amount of time spent the last 8 months on ur videos. As always. Thanx again man

[@christopherbarone3602]

Great info used this info to fix bad cat on 05 Ford Taurus had down stream o2 stuck lean watched video again and found the bad sensor thanks Mr danner

[@malisa696]

I like this video. I had some issues with troubleshooting catalytic converters. With my scanner I can see in frame data oxygen sensors mV and buy looking them I determine is the catalytic converter good or bad, but I can not be 100% sure. I do not have graph mode so I am relining on numbers I see. Now, I will do more measurements with scope as in this video. It is very important to tell to the customer in 100% that converter is good or bad...not just to assuming.Great video Paul.Thanks so much.

[@johnnysprocketz]

The most brilliant mind to ever do the dam thing, the brother too is impressive. Would give anything to be a fly in the wall at that shop for a day.

[@jjones9290]

How goes it Scanner Danner! Just wanna say thanks so much for taking the time, initiative and having the care to make and post these videos! I have been working on a car with all the symptoms this one had and just learning to read scan tools and the graphs on one and I'm hooked! I have never looked at computer diagnostics this way and frankly I'm fascinated now and want to learn all I can bout them! I'm almost certain at this point given my data and after seeing this video( not to mention the chunk of ceramic honeycomb that blew out tailpipe on test drive[good thing I stopped to see what noise was])I most definitely have bad cats and probably caused from dead O2. I'm headed over to your website now! Please keep up your channel and fine job thus far! You're a fantastic teacher!

[@mauriceupton1474]

Thanks SD you have one of the most informative channels on KZbin !

[@antor.j.medrano]

i love how informative this video was, I already knew this but i wanted to super make sure this how it actually works.

[@ScannerDanner]

It will depend on the com protocol as well as the scanner used and how many data PIDS you are displaying at once. So it is not set and cannot be relied upon for a time base. Unless you has a run time data pid to compare next to and some cars do provide that PID

[@abdallahmohamedgelwah736]

Really it's the best and perfect explanation i have ever seen,,,, thanks man ,,,translate this quote and mention the speaker ( الهندسة كما يجب ان تكون )

[@BigEightiesNewWave]

Gold Standard stuff here, bookmarked, notes taken and saved.

[@johnferguson7235]

How much propane are you introducing? Do you just keep injecting more propane until the short term fuel trims respond with a full rich signal? You are the master of the scanner; love to watch you work. You capture the info on the video quite well. The extra effort shows.

[@mikenelson3102]

I cant remember who or where i picked this up from, but emission systems now a days (unsure of when "now a days" started) have the ability to randomly try and set CAT codes by adding fuel and waiting to see proper response from downstream O2's. O2 spacers is what i suppose emission standards are trying to make obsolete.

[@richschaff5504]

run scanner for 60 seconds and determine how many frames elapsed. Divide 60 by the number of frames. The result is secs/frame.

[@HighestRank]

How about just watch as it puts the live frame numbers on the screen? Looks like it marked every other frame.

[@Wes_5kyph1]

All I'm getting on an '09 2.4L Toyo Camry is this lone P0420 code. Sensors were all replaced a 2 months before the CEL even came on. Going to try some fuel additives, maybe even inject water/ammonia to steam clean. Too bad located an exhaust leak isn't as easy as finding an intake leak.

[@joemasterman4305]

I have been gathering O2 storage numbers off known good cars lately, I am seeing 2-4 seconds on average as well.

[@Dwohman]

Thank you for the info, it helped me read my maxicom mk808. Now I know what I'm looking at.

[@Dark_Knight_USA]

Greetings: Based on the data provided I tend 2 agree with the final diagnosis and customer advise. Thx 4 the share.

[@jamesvdl3583]

You are right about using a factory cat. I was talking to a sales rep for an aftermarket cat company and they told me that their cats did not flow the same airflow as the factory's flow.

[@ScannerDanner]

IT is not a flow thing. It is a precious metal thing. The factory cats are using either more of those metals or different types that are more effective. There is a reason that aftermarket cats are not worth much to a salvage yard compared to a factory one.

[@MRMAN-wb1tv]

*I replaced THE COMPLETE exhaust system on my 04 gs300, and the 4 O2 Sensors, but one sensor Bank 1 upstream threw a code, and it was simply an exhaust leak from bolts backing out*

[@mlb0611]

I have solved many issues with reflashes, including Cat codes, all they are doing is raising the threshold for tripping a 420/430 codes on those reflashes

[@IMFDB]

GM's newer vehicle have way higher standards for monitors converters. They use 49 known working converter samples saved in the ecm and compare it to the actual suspected bad converter. I've seen the rear 02 sensors not fluctuate and p0420 still sets. People that commit emissions fraud by modifying the rear 02 sensor to fool the ecm are probably the cause of these high standards on new vehicles make it difficult to diagnose and requires a lot of brain power and reverse engineering the techs may not get fully compensated for.

[@TheMagican614]

customvideo454 why do you think so many techs just throw parts at vehicles. Because if they don’t they won’t make any money!

[@jkdatlvnv]

As has been mentioned by ScannerDanner, you need to know about what you 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. The best way to test a TWC 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. 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 offering 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

[@r.weaver3769]

Mine shows P0420 and P0326. 2007 Hyundai Entourage, 205k miles. engine reportedly was replaced @ 38k. The only time the downstream mimics upstream is after idling for several minutes, bring RPM to 2k readings normal, and remain after return to idle. after about 7 to 10 minutes symptoms begin to reappear. Am about to attempt propane test using lab scope, have not tested KS, yet.

[@whitehistorymonth3563]

This is one of the best videos I've seen on KZbin. Now. I just need money for an expensive scan tool. I bought the $44 one now. I'm like damn it.

[@Jake-me4ze]

Harbor freight $75 Zurich zr8

[@nathanielmoore5677]

Best explanation video for cat efficiency codes I’ve seen. I’m getting good oxygen sensor behavior but yet throwing cat below threshold codes on both banks with brand new cats…I can’t bring myself to risk it and throw factory cats in if it’s not going to solve the problem 😬😬 2007 tahoe 5.3

[@ScannerDanner]

Factory cats unfortunately my friend

[@ScannerDanner]

Or an anti-fouler in the rear O2s 🤫

[@nathanielmoore5677]

@@ScannerDanner I put them in both rears today haha we will see 🤞🤞

[@GoogleAccount-ii9sj]

@@nathanielmoore5677 did it work?

[@sirsweetness8332]

I think you are an expert! You are humble. 😊

[@ScannerDanner]

Thanks for the reminder about Mode 6. I rarely use it and should more often

[@stage3performance]

I just finished section 4 & 5 in your book so this video was posted just in time! Thanks Paul

[@dandearman2871]

I just bought a 2018 GMC Sierra with 17500 miles. It wasn't a day later I had a check engine light and the engine was running rough. I took it to the dealer and when they test drove it they got stranded and had to get towed back to the garage. Ended up the fuel pump died on them and they replaced it. I picked it up in the morning a few days later and that night got another check engine light. Took it back the next day and when they checked, it had the cat efficiency codes. They replaced all of the catalytic converters and the down stream oxygen sensors. The story I got was this truck was part of fleet the oil well guys used and they may have let the truck run out of gas and maybe that damaged the fuel pump? What could they have done to damage the catalytic converters?

[@Jonathan-us4ig]

I prefer to monitor the issue the same way the PCM monitors the issue. Watching sensors on a propane enrichment test is perfect. Checking cat temps gives you an idea if the cats are alive, but won't give the same in depth answer as reading the signals from the PCM.

[@knobrush]

06 Dakota 4.7L v8. last august(about 130k miles) I replaced the cats/y-pipe and all four O2 sensors. Check engine light came on yesterday. P0420.

[@ScannerDanner]

Aftermarket cats are junk. You're lucky you got a year. I've seen them flag a 420 after 2 months. Make sure there are no exhaust leaks before pricing a factory cat

[@knobrush]

@@ScannerDanner No leaks right now. But interestingly all the Dodge parts sites show "discontinued" but they're still available through Mitsubishi parts sites. 52013780AB

[@eric63377]

Good write-up/ video.. And customers wonder why they are paying 120 per hr + to diag their car.... Also I had a 2018 suburban I installed an aftermarket cat on and it threw code as well for it.. rechecked data and it wasn't enough oxygen storage.. so I installed a FACTORY GM cat and all was good after that...

[@mofeedfouad7391]

That's was a GREAT DETAILED INFORMATION ... Big thanks

[@vsboost]

Hey Paul, Great video, i just fixed a P0420 on a 4cyl Barina, turned out the cat was blocked up (full of carbon deposits), the car LTFT was at -30% and the car was bogging down on load, in this instance i did only a back pressure test to give me direction, i will try using this method if i get the chance.

[@Loyalvic89]

Awesome! I just had a car (same make and model as this one,) in the shop with the same code. I did the same upstream/downstream O2 comparison and found on bank one the frequency and amplitude were identical. I also did the inlet and outlet temp test and it really wasn't conclusive like you said it wasn't. I didn't know about the oxygen storage test, thanks so much for another test to put in my repertoire!

[@Jason607]

I love these videos and have learned some things about them. Nice to see someone who actually test and not just read the code and guess. I have a question about one aspect. I have often had cars come in with cat inefficiency codes but if I see other engine issues such as EGR, MAF, MAP, upstream O2's, misfires, or vaccumm leaks and I usually fix those first and clear it out and let it go and see if P0420-P0430 comes back. My question is will a good cat show that it is inefficient with other running problems or is it safe to say that cat is on the edge of failing anyways? I don't want to diagnose something to be a problem if it's really not but then I don't want to temporarily fix something just to give the owner a headache down the road.

[@ScannerDanner]

I handle those the exact same way Jason. Especially O2 related faults.

[@geoffschulz]

Excellent information! Very thorough, very useful!

[@PhilArttz]

Thank you for this video, I finally understand how the sensor values work and what they mean. Now I can diagnose my sisters P0420 ^~^

[@jaygames1980]

This brings more light to my old schooling.

[@davidbellmechanical]

1996 to 2000 wow that's 4 years of storage time :)

[@debtfreehouse6216]

A very knowledgable teacher, thanks

[@sivucit]

Very Nice.. Paul. You always stand outstanding..

[@autohublibya2870]

Great effort, and greater information. Thank you a million for your time.

[@JoelAutomotiveInaction]

nice video it support you eBook cat testing chart, Paul what test method will be better to apply when I have a/f sensor on upstream? , at this point I can not compare upstream and down stream , thank you very much for this upload.

[@ScannerDanner]

Do not touch that cat. until you have fixed your running problems

[@rodger6940]

Why in the 04 Mazda 6 is p0430 camshaft sensor

[@larryvercher9809]

Danner your car should always run perfect.

[@mikewithers7685]

during your tests the o2s22 seemed to be lean at 200mv. thought at or around idle should be around 400 to 600 mv ??? is this normal ?? or what should the o2s2 read. thanks Paul for great videos !

[@thatsubae]

Great stuff man, that propane test is on point 👌🏼

[@carlthome6004]

Excellent. More 'tools' available in the bag. Nice job.

[@faustogonzalez8397]

Thanks Paul, awesome as always !!

[@therealspixycat]

May be combine the up/down o2 and stft/ltft? The ecu can trim the very low stft very rapidly when you cut off the gas?

[@advancedleveldiagnostics]

Great info, Thanks for all your videos, I feel like I'm always learning something new from your videos! Does service info ever give a time frame for the oxygen storage test?

[@ScannerDanner]

not that I am aware of my friend

[@victor35ma]

Nice thanks for your master explanations. hope when you have a chance to make a study case for P420 and P0422 on Nissan Maxima from 2002 to 2007.

[@ScannerDanner]

I don't plan on making any major changes. some additional hyperlinks added for quick reference to my youtube videos maybe. but these can be found in my playlists I have recently created for each Section in my book. So you are good to go with the paper version if you like. Any brand new material, say a new chapter on GDI would NOT be added to either the eBook or paper book. It would be separate. (We are talking a few years away from now before that happens, I need my own case studies first)

[@leemassey9065]

Awesome video..I've got a 2008 Dodge Challenger SRT 8 that keeps throwing a check engine light. First it just came on, and this last time the check Engine light was blinking off and on and the car was running very rough. So I took it back to the dealership. They said they replaced all 4 O-2 sensors. They drove it, and it came back on. Same code as begore. It said Fuel trim issue, lean bank 1. They are telling me that the computer is reading the codes like the catalytic converters aren't working up to Federal standards for emmissions. Needless to say, they've had my car for two weeks and can't figure it out. Do you have any idea what it could be?

[@ScannerDanner]

@@leemassey9065 a blinking light is a misfire code and rough running suggests a misfire too, it is not the cats, take it to someone who know how to troubleshoot

[@HotRod-wv4vm]

Excellent explanation on catalytic converters 👌

[@wesleybrabant3595]

Everyone know Scanner Danner. Great video Dan.

[@SS-zl3go]

Nice video. Just a reminder the cheap infrared thermometers use a "cone shaped" view form the front of the instrument. The further away you are, the larger the sample area. The laser that they use is a little misleading. Its meant to be a guide only, and is NOT the actual point that's sampled. Evidence of this is true as your readings were fluctuating all over the place and its unlikely the temperatures were that different within a half inch of pipe. It was probably seeing the difference between the surface temps of the pipe and heat shield. Anyway, for purposes of catalytic testing, its a good tool and you did show the concept well. Just don't use the temps as absolute because these instruments have their limits, especially ones w/lasers that suggest a pinpoint reading.

[@johnferguson7235]

+Eric “ss195” G You can drill a small hole in the exhaust pipe and place a thermometer directly into the exhaust both upstream and downstream of the CAT

[@geraldschiffmacher8282]

Great video with oxygen sensors, how about with lambda sensors. How do you verify bad catalyst with lambda sensors. Thank you.

[@ScannerDanner]

To be honest, I never do this test. A bad cat (not restricted bad, but bad in that it no longer can catch and store oxygen like it should be) will set a code and that code (P0420, P0430) is very accurate as long as there are no other codes or exhaust leaks. No other codes but a cat code = you need a cat 99% of the time. Further testing to confirm not needed imo

[@joey1917]

Thank you for the video is very helpful, can you tell me what was the root cause that made the CAT go bad ?

[@ScannerDanner]

so many things! Misfiring, fuel imbalance issues, oil burning over a long period of time. Anything that makes the cat overheat will kill it. It sort of smooths out all the little nooks and crannies that catch and store oxygen. Then when it gets too hot, it will melt all of that together and become a restriction. Also, contamination can occur from all sorts of things from the fuel being burned to the oil being burned. In theory, they should never "go bad", but they do. Sometimes there is not a cause that you are going to fix. In fact, in most circumstances, that is the case. As long as your fuel trim numbers are good and you have no misfiring and no driveability problems, change the cat and you'll be good for another 150K. But NEVER use aftermarket cats!! Factory only, unless you want your P0420 code coming back in 2 months.

[@ScannerDanner]

Thank you Michael for your input.

[@billswanson1730]

Not a mechanic but appreciated the education

[@Charkatak]

Very informative video! Few days prior to watching this video, my friend asked me to look at his 2015 Ford Explorer(ex Police Interceptor) with 92k miles. My knowledge about cars is limited and this video made it obvious :) Basically his car showed a check engine light. The code with got was P0420 which seemed to be Bank 1. I told him that the code means something is wrong with the way catalytic converter is working. I looked at the live data and marked 4 oxygen sensors and fuel trim data to see the graph. With my limited tool, I did notice that one of the oxygen sensors was marked red and was fluctuating a lot. From your video I now understand that upstream sensors should/will fluctuate, but downstream should usually be less active(when at operating temp). Also his STFT is at least 22%+ or more, but LTFT is at 0%. 1) So this P0420 code always means downstream reading is not efficient enough? 2) You think Cat is the issue here?

[@abcdefgh9138]

Great video, as usual! My experience agrees with yours; it's not uncommon to have a low-mileage vehicle with no running issues and bad cats. Have you had any cases of cat codes that were solved with a software reflash? I.e false cat code that didn't return after applying an update that addresses such issues. Thanks!

[@captroy2527]

the temperature test is a quick test and in theory that is how it is supposed to work the cat will heat up and burn of any unburnt fuel so the rear should be hotter then the front

[@forester_overland_nz]

Thank you for creating this video!

[@grumblesaw4415]

Hey in this video you show the custom configuration screen on the snap on unit, for the life of me i cant find the st Fuel trim. Also what does the MNTR (HO2S1) B1), stand for? Both HO2S1 MNTR (B1)AND H02S2 MNTR (B1) show lean. 2006 xtrail 2.5lt. great video

[@snivesz32]

Question: If you’re doing an oxygen storage test by making a rich condition using propane and then removing it, to see how long the cat stays rich, it’s not testing how long it holds onto oxygen, it’s testing how long it stays rich. Which seems to me more like measuring how slow the gases flow through the cat.

[@jethzeeltorres9727]

Awesome video. Thank you for sharing your knowledge. ⭐️⭐️⭐️⭐️⭐️

[@wingman358]

another great video, very informative. you're one of the best. thanks Scanner Danner!

[@HighestRank]

He's already denied being a god.

[@g.s.7383]

I got a sluggish upstream in my Volvo S60 II 3.0t t6. It just stops working for a couple of seconds or longer and then restarts. P0420 ready in no time.

[@hitmonRay]

how do i tell if a sensor needs to be replaced or if the cat needs to be replaced?

[@Junk65]

Great info. Great instructor. Great video!

[@canuckfixit7722]

The takeaway is that a bad cat behaves like an open pipe such that USO2 = DSO2. A good cat will show a quantifiable difference between O2 readings as well as a temperature difference.

[@marktemple5275]

A very informative video. We sell aftermarket cats & was hoping to link to this video until you basically trashed aftermarket cats. I respect your opinion & are correct there are bad aftermarket cats. But it is unfair to condemn all cats unilaterally. We've been on the web successfully since 1997 & sell only quality cats from Catco/AP, Walker & Magnaflow. Sorry we can't use your video, but again respect your views, just do not agree. Appreciate your expertise & thanks for taking my comments.

[@ScannerDanner]

If you have MAF codes or fuel trim problems those MUST be corrected first.