How to Check a Catalytic Converter for Blockage or Efficiency Below Threshold Issues 

Excellent information. You really know what you are talking about. A truck I'm working on was showing 2 of the very symptoms you mentioned. Lack of power and transmission felt like it was skipping. I removed the O2 sensor and there was a big difference. Lots of noise and some smoke but the power came back (to some extend). Truck has 256k miles, so. Keep it up my friend. 👍🏼 If it helps anyone reading this. Do not be deceived with the O2 Readings You can have good readings on both Pre and Post Cat sensors. I didn't have a Check Engine light on (No Pending Codes either) but the symptoms were there. Good Luck everyone.

Watched 50 vids on this after a guy tried to sell me a remanufactured transmission for $2000 .....very helpful......also can cause high rpms and major drop in acceleration

Thank you for covering live data of the O2 sensors in such a simple manner. Too many other guys go on for 40 minutes about rich lean readings when all most people want to know is what they should expect to see and what is wrong.

I failed at checking the O2 sensors. lol I didn't have the tester with the clamps. There was four sensors and had a P0420 code popping up. I keep watching these videos and realize what you said about the warrenty. Called GM for my 2009 Tahoe with 129 700 km and still had till 130k for warranty. Called Chevy and initially was told there was no warranty until I strait up cut him off and said I spoke to GM about this coverage. Went to Chevy and still was trying to test my knowledge which is pretty much the knowledge thanks to your videos. Later got a call and was told the part was being replaced and going to be ready shortly. I was told the cost was over 1400 and im sure that didnt include labour.. THHank you very much for your videos

Thank you for the info! I like your voice and calm/funny delivery. It would be cool to swap car stories with you. Best wishes!

@14:41 you should be checking 02522 O2 sensor (Bank 2, Sensor 2) but took reading from 02512 (Bank 1 , Sensor 2) again! Already determined that Cat was bad just previous. I got the updated OTC 3208 scanner and it works great. Thanks for this video explaining how to use it.

2:55 You’re the only one who gave me that excellent info and that is what my car is doing, my cat btw is melted.

Thank you for your step by step instructions, suggestions etc.

awesome video. answered all questions. i am replacing my oem manifold with headers. thanks again!

great video man! nice to see the temperature readings and see something that is straightforward.

I'm having an issue with a 1997 Jeep XJ 4.0 that may be a blocked cat and I thank you for the tip to loosen the bolts on the exhaust manifold flange which I'll do tomorrow. Thanks again.

Car diagnostic professor. Better than college 😊thank you , star 👍

Thank you, I'm teaching myself about vehicle repairs and I found this very informative.

Thanks for the video. I was having a problem with sputtering at low rpm and my bank 2 came up on my CEL code. This might have shed some light on an issue i didnt think about. My f150 is a 99 4.2 bought in june of '15 and this might have been an issue building up over the year. So this might actually help me alot. Also i just fixed the IMRC retainers due to that cel but had to drive it like that for about 1-1.5 months. Lol not much time to do anything. But this coulda been the issue.

Bro, I love your videos. Very very helpful. Keep it up.

Great spot on! My hyundai had a CEL on but they are are replacing it with no charge. Back in love with my car. This item is on back order possibly two months out, though.

Another great video and information from RatchetsAnd Wrenches!

Thank you for this videos.... Ima smarter because of you.

this guy knows what hes talking about

Hey guy; Thanks as always for your informative info. Got a make or break me question. Sorry to be so windy but I feel info is crucial. I picked up from an older gentleman a 2004 Dodge Durango 3.7 with 112 thousand original miles. Spent much of its life in a garage. It ran like crap and barely got home. I replaced original plugs & coils and she started with the multiple misfiring probs. in between small periods of smooth running I noticed she was running to warm. I plan on keeping so I Replaced Water P, Thermo, and hoses. That helped but still warm. So I called a local ole guy that has been working Radiators for all his life, told him some history and he wanted me to bring it in. He showed me his test Sure enough it was. I put new one and she is very happy. I tinker and get myself in trouble regularly. I was getting dizzy with the coil plug switch game. She idles rough and coughs and sputters trying to gain speed. I took to a local garage with written down history. They said It needed a better quality plug. While there I had them do a compression & leak down tests. They were impressed with results. And the she ran rather awesome for 200 miles. Then back to same. They first mentioned catalytic converters, But I thought with only just over a hundred tho miles they should not be the issue. I just caught your vid on testing the pre /post cat temps. Bank 1 which seems to have the majority of misfires the cat temp after heated a bit were almost 600 and close to the same pre/post. Bank 2 post was +80 form pre. You mentioned it must be significant difference. So here I am/// I do want to keep her. I can do the installs. OEM Cat Y pipe is about $500. My exhaust muffler is swelled so That will be about $300. I've already put 2 new rear 02 sensors. I'm just confused as when the "correct" plugs were installed she ran very well for the 200 miles. I would just like some (a little) reassurance this will cure my problems. Best; Tom

Awesome information brother 👍 thank you so much God bless you

Super good job man, thanks!

Great video! I thought I had trans problems! Thanks so much for this information!

Great video. The concepts were simply put.

I gotta be honest when the vid first came on, I didn’t think I was going to learn much. How wrong I was!!! Great video Bro, you know your 💩!!!

this helped a lot totally what I'm going through with my 1993 Honda accord lack of power can't even go over 20mph

Nice video, good summary. I made a little adapter from an old O2 sensor that goes into an O2 sensor threaded hole, allowing me to measure backpressure in front of the cat. Works great but I don't often use it.

this guy knows what he is talking about

You always give very valuable information man and you explain it so good , very very well explained and it’s very obvious that you really know what your talking about , I been trying to get my truck to pass smog for 7 years , I had lean codes galore that wouldn’t go away I changed O2 sensors both cats with used ones off another truck still nothing , my kNn cold air intake nothing Fuel injectors still not ready , cylinders coil wires spark plugs , next I think I should Check my ECU , I wish I could barrow you for a few hours so we can pin point the issue

i like this guys videos for some reason!

Thanks for the video and good info.

Awesome job explaining everything 👏

very good and clear info ... thanks a lot !

hey your vidios are very well done and well explain for person with a little knowlodge on car thank you

Eric, thanks man very very helpful! 👍

very nice video with useful information. thanks

Thanks for the info I really thought it was my transmission

10q sir you add some improvements on my knowledge about emission systems

Nice video! I must say u made a long way since then. Keep up the good work! My Chevy Sonic has the exact problem, during gear shifts sometimes car shakes back and forth. Feeling like a transmission problem. Car has no codes. First I thought it was transmission but after seeing your video I tried to give it a shot. My cat and exhaust manifold are in one piece so removing them and going for a drive is technically impossible. Should I remove the first o2 sensor and go for a drive? Thanks in advance

Great video man thanks for the upload,great help

great information

Great video, thanks. A year ago I had my Catalytic Converter replaced. couple of days ago two codes came on P0420 and P0430. When checking a live data the A/F Sensor before the Catalytic Converter has no movement on the scale but the one after the Catalytic Converter is jumping from high to low constantly. How would I even check if the precut sensor is good or bad. Also, I think y this car had 2 precat and 2 postcat sensors. 2002 Rav4. thanks

I have not read all the comments and am not sure if anyone has mentioned this before. But @ 7:47 in your video, you started looking at readings from the 2 Bank2 Oscar sensors (meaning O2s21 &O2s22). You read the first one (O2S21) correctly but @ 8:09, and while you thought you were looking at readjust gs from O2S22, the display on your code reader was actually displaying the readings from O2S12... which is why you thought "what do you know, it's behaving like the post-cat on bank 1". Just thought I'd mention that. Otherwise, very informative a day understandable. Thanks.

Great video

Very good explanation Thanks

Really like this guy

Great videos. Thanx.

So if I remove the Pre Cat 02 sensor, and take it for a spin, what do i need expect and diagnose? and where is it located

good info. thanks

Being from Australia, I love our Native plant in the background. However, it's not native to where you are, and poses a significant problem in bushfire season. Like the way you explain stuff.

I have an Oldsmobile Cutlass Ciara that has a host of problems. When I drive like you said it feels like its being pulled back, take off some times shuts down or has no speed. This past weekend I had a gas filter leak and now my car is making loud muffler sounds, knocking but all the noise seems to be coming from the tail pipe are but I smell gasoline in the front. There is no scanner for OBD 1 scanner so now its a guess game from these mechanics. Its a 91

Perfect video

nice tutorial,

i seen how you tested upstream o2 sensor with torch in a previous video. is a downstream sensor tested the same way? i do want to check that to make sure it is good before i say the cat is bad.

Thanks for the vid

can you gut the cats in a 2003 escalade 6.0 awd and it not have bad effects on the engine?

Thx for your videos buddy! Q: would I’d be ok with a after market CC, or I must use dealer cc instead.? Chevy traverse 2009 ...thank you in adavance

I have a 2011 Chevy Equinox 4cyl. and the engine light comes on and the computer says PO420 Cat. convertor Bank 1 code comes up. Would my convertor be covered under the federal warranty? Thank you so much +Ratches and Wrenches!

gdm!! charles!!! my question is I have a 95 ford thunder bird 4.6 v 8. my catalyst converter. car smokes but no engine light and it has power at times.even tho it runs good.

Hey, I have a question whether my Cat really is bad or not. I got the P0420 code for a couple weeks and been going through a checklist on symptoms. The car seems sluggish lately, and will not accelerate quickly anymore, I have to slowly increase speed. I tried accelerating faster than normal and had a cylinder misfire with the P0300 code and Torque Management P2637, which eventually disappeared after 5 minutes. I cleaned the throttle body and MAF sensors, checked the ignition coils and spark plugs and all seem to be fine. The 02 sensors seemed fine on inspection. However, when I measure the temperature around the Cat, the inlet weld is about the same or up to 70F higher than the outlet, this infers a bad/clogged Cat. What I don't understand though is that through the OBD2 voltage readings, the pre Cat 02 sensor oscillates rapidly around 0.1 to 0.85V and the post Cat sensor is fairly steady around 0.8V and only dipping to below 0.15V when I push the gas. These readings tell me the Cat should be fine though, but the temperature readings tell me otherwise. Should I go ahead and assume the Cat is bad? Can I drive with the Cat removed just to see if the car responds as it's supposed to under acceleration? Thanks!

Great video !!

Thank you I think that's what is happening to me but now my van is making after having the van off for a while I hear a pop sound like a water bottle makes when it's cold to warm up but coming like under the van it sounds like from inside because when we put the heat on it makes a rumbling sound

you're awesome!

Awesome 👌 video tutorial I recently pull my cats on a 2000 V8 Ford econoline it has three cats and I noticed the main cat in the middle on the inside was gutted out the web piece was not there what's your suggestions on it being clogged?

Nice video

Nice video, definitely thumbs up

Thank you

Thank you for the great video, was very helpful in my situation… Was curious if you could help me with My issue. So here goes, yesterday my car passed the inspection and omissions test with zero issues or errors. This morning I wake up and have a check engine light with the code P0430 bank 2… What in your professional opinion do you think that could be? And it is OK to drive for a couple days before I get it fixed? Thank you very much look forward to your response and keep up the great videos

Good job! Are you saying, I could read Oxygen sensor data with my code reading tool?? I have one, nice one, so I could test my O2 sensors, before and after catalytic converters??? I have to do that, since I have that code, P0420/Bank 1 every now and then! Could those O2 sensors go bad too, can you clean them?? How about bad sparkplugs/ coils?? I already bought new sparkplugs, haven't change them yet! thanks, youtheman =) My car Infiniti FX 45/ 2004, about 118000 miles....

hey I pass smog but p0420 cam on? any ideas what it might be

Could an issue with the cat show up as either an up stream or down stream O2 sensor code? Asking for a 2013 Nissan Versa.

Great video, about the code reader it looks like they discontinued the one you show in the video.Is this one the same with the live data, Autel AutoLink AL319 OBD2 Scanner Automotive Engine Fault Code Reader CAN Scan Tool or Bafx Products - Wireless Bluetooth OBD2 / OBDII Diagnostic Car Scanner & Reader Tool .Thanks one more thing will it pick up the bad cat while warmed up and running because the problem is only happening when i'm doing 50 to 80 mph i smell a rotten egg smell bad coming from the dashboard area .The vehicle is a 2013 ford edge and how do i find out the correct volts for my vehicle.Thanks

@1:50 these symptoms can happen specially on hot weather or it doesn't matter? What if you live in a cold area does benefit the performance of a bad catalytic converter? Please help

I got a check engine light on my jeep Wrangler , i scanned it and it was bank 2 sensor 2 ( p0057 ) . I changed the o2 sensor , but the check engine light is still liuminated after 40 miles .. do you think its bad catalytic converter ?? Please reply

“I know what you’re thinking” 😭 I lost it, because I was.

Very helpful. I'm glad you said that it can resemble a transmission issue and that it can give misfire codes. Thank you for sharing!

How do you test for the MAP sensor, bro? My cat is bad but I think it may have been caused by a bad MAP. I have the 2009 btw 335. I get the code 0172 bank 1 too rich. It used to to 0301 code and was misfiring. I replaced all the file injectors the misfire code went away but 0172 stayed. I tested the cat with the infrared thermometer like you said and found one of my cats was bad. how can the MAP sensor be tested or if you have any other ideas you can share. Thanks

GOOD VIDEO!! JUST ORDERED NEW CAT.

Thank you this was very informative. I'll be watching the O2 sensor video next and I'll be under my hood tomorrow! Hopefully I can get this car back on the road.

My respect for you from Iraq

My Reno has come up with the catalytic efficiency below threshold one and also check anti pollution systems,does that sound like it?x

Mentioned it could mimic transmission problems. Could that cause stalling putting it gear in an 08 Patriot 2.4?

my man knows his shit nice videos man everything is very well explained well done

The thing is, or so I heard, that if the CC is even 1% less than 95% efficient, it will trigger the check engine light. So if you're doing the temperature thermometer or another test, it might show similar numbers as a one that is 95% efficient, so the test wouldn't really work. Correct?

i have1998 ford 150 4.6 engine everything works fine no trouble codes but the cat dot on my scanner stays red

My car is a four cylinder stick shift and it's giving me trouble with a 3000 high rpm all the time do you think it's the catslicti.

With a faulty Catalytic converter.. meaning at operational temperature the post CAT o2 sensor copying pre CAT sensor, would this create a Lean condition on the LTFT around about +17% LTFT lets say, thus Looking like a vacuum leak ??

Compadre! Si comienzas a hacer tus videos en español tendrás muchos más suscriptores y muchos más likes en tus videos. By the way your videos are so helpful.

hi my o2s12 has a steady reading in the 0.700 range would you say the cat is fine? thanks

Have you heard of people using lacquer thinner is that safe or what’s your opinion thanks

I've developed a mini misfire no CEL, I have a 2012 Toyota Camry I used to get 25mpg. Now I'm stuck at 20. I noticed the stumble when it's at idle and in neutral, no symptoms when driving but when I stop at a light in drive, I get a vibration, also not all the time but there's instances when my trans shifts like it's slipping badly, and others when it shifts like it only has 114k on it think it could be a clogged cat? It's attached to the exhaust manifold which isn't cheap or just a leak? It can it possibly be both?

Hi there I have a 2006 Mitsubishi eclipse. I parked it and did not drive it because I was hearing a noise coming from the exhaust/Catalytic Converter. So I believe that is what it is? When the car is cold is when I hear the sound the most. Every time I take it to my mechanic (2) mechanics they say it's is safe to keep driving it. I am so frustrated. The noise use to go away but now stays. So now the sound sounds like a little rattle which sounds like vibrating for the most part. Also experience small misfires some times, but no always. Never loss of power. I just don't want this to get worse. What should I do. It's like going to a doctor have to keep trying difference ones to get the right diagnoses.Like your video by the way, it is educating for a girl lol.

Thanks for the video. I am trying to diagnose my own catalytic check engine code too. Question is how can I diagnose other engine issues that caused my catalytic converter to go bad? Thanks.

Thanks for posting this. I am pulling my hair out trying to figure out why my car can barely accelerate out of its own way. I had a hunch it was the cat because of a misfire caused by bad coil pack about 8 months ago. Unfortunately i couldn't fix it right away, being too broke to buy a new one until I saved money for about a month : ( Life's a bitch when you don't have money thats for sure...fortunately knowledge is invaluable and there are people like you who are willing to put in the time and effort to share it!

You showed the same sensor, O2S21. Bank 2 post cat is actually O2S22.

I have a 2011 ford escape xlt and my car was barely moving, and I heard a loud pop sound follow by a bad odor and the car started driving normal again. What do you think is the problem?

What about a car wash, would it be able to get in underneath and cause it to go bad. I have an f150crew cab tritonv8 and I didn't pass 2 times.

On that Audi: the test was inaccurate- you went through the motion of Bank1S1-Bank2S2, but you went to what you thought was Bank2S2. The scanner screen showed you went back to Bank1S1. Rewatch your video

what happens if the O2s12 has a negative voltage?

Omar, I thought the same thing.. when checking out the second cat... you read the readings for bank2 sensor 1 , but then you read bank 1 sensor 2.. ? why? 8:10