BMW E46 How To Diagnose a Bad Catalytic Converter P0420/P0430

A P0420 code indicates a problem with your bank 1 catalytic converter and a P0430 indicates your bank 2 is a problem. Even though I only had a P0430 code stored, you will see that both of my cats are indeed bad. One thing I didn't show was the codes that are read from the DME (engine computer) by INPA (an enhanced mode bmw scantool), but I did check them and both catalytic converters were indeed reported as problems there.
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Exhaust Manifolds Removal: • BMW E46 Exhaust Remova...
Exhaust Manifolds Reinstall: • BMW E46 Exhaust Manifo...
This video is for entertainment purposes only. 50sKid assumes no liability for any repairs or modifications performed by the viewer as a result of the information contained in this video.

[@mike.135i]

yesss! these types of videos (diagnosing,,common issues what to look for etc) help so much

[@peoplehear]

Great video buddy, the explanation with diagrams and steady tempo of what and why!

[@mathewross-brooks5164]

Bro where have you gone!! You are my go to for E46 help hope your doing ok!

[@flyhacking5830]

Very informative video! Thank you. Although I don't have any issues I'm gonna go out tomorrow and observe my post-cat O2 sensor voltages

[@AnthonyStromDesign]

Great explanation on how to read the O2 sensors. Old video but still current information!

[@jaimelobato3818]

Your videos are very important to me for clarifying certain defects in BMW. Here in Brazil our fuel is very bad causeng many defects in the sensour ...Thank you...!!!

[@jameslatimer1432]

Put vaporized water through your engine inlet intake ,,manifold spray bottle keep revs at around 1800 rpm cleans every thing carbon no more ,,

[@bunnyboyy1410]

Fantastic video! Been looking for a long time for someone to explain this better.

[@MindHunger]

I had the same codes on my E39 530i. I was advised to replace both the intake and exhaust VANOS solenoids, then clear adaptations for the DME and transmission. The codes went away for good, and low-end pickup noticeably improved, like I had a new engine!

[@stewfly9227]

I really enjoy this content. I had p0455 evap code and fixed the obvious worn 2nd air pump hose... fixed the code but I also have p0174 and p0171 LEAN vacuum leak codes and p0420 and p0430 CAT below threshold codes. trying to pass emissions but these codes are confusing. on one hand it could be simple stuff but on the other hand could be very complicated. I am a very beginner mechanic via youtube and 50's kid content so I'm really trying to learn about the 2003 325is and their problems first before I take things apart and can't re-assemble them as the car is running decent. I have an odor coming from the engine bay like a really oily gassy engine. the temps on the passenger side engine bay seem pretty hot to me... based on my codes and what I've written here can the internet people spring to life and help me out without saying "just buy all new stuff" or "go to bmw mechanic". Thanks anyone who cares. (really need the support) I have new o2 sensors from bosch on hand. recent oil/all filters changed. plan to smog soon... thats all I got

[@sunjoomoontube]

Awesome, clear and scientific methods. Big thanks.

[@Wellsotuning]

First!! We love you 50skid! keep up the good work!

[@george5022]

Brilliant Vidio as always Jason, I always learn something New.

[@jaimerodriguez7917]

Thank you so much just what I need it cause I wasn't so sure about the post sensor how they work thank you once again

[@frankendoodle6379]

My car is having acceleration issues. Runs like shit from a cold start, this was never an issue before. If i pull out onto the road, its so slow right now, i'm scared to get rear ended. Having trouble climbing hills, i can barely gain any speed if any at all. If going uphill 65mph thats probably as fast as it"ll go till i get on flat ground, or downhill. Car doesn't shake or have any vibration. Changed a poor looking coil, put new ngk plugs in. Car still doesn't have acceleration. Took it to get it scanned, 4 codes came back for cat issues. I've had these pair of headers now for 2 years, its about that time, then flash tune to delete sap, and lower o2 sensors. Thanks so much for your videos, you've helped my dad and i with this car for the past 3 years. You basically taught me everything i know about this car, and shop life. Thank you 50's kid!

[@frankendoodle6379]

Ended up being a failing maf. Much cheaper fix

[@arturmirzoyan4744]

Have an 08 x5 3.0 with similar codes, looks like might have to do this on it. Got a regular scanner, gotta have to double check to see if it is the issue. Thanks for the video 50skid

[@fieldsofomagh]

Gamble paid off, looking good ! Get ready for booster rocket ignition.

[@lambertotejada7769]

I have the same problem my 2005 Grand Caravan the O2S1 is oscillating lean to rich and the O2S2 is about .7 but when I rev the engine to 2000 rpm the O2S2 oscillates like the O2S1. Thanks to this video; I will put new convert to this Van.

[@one_love3145]

50sKid, you are my auto hero

[@martinv261]

Very useful video. Many thx.👍

[@raypooley1312]

Hi Jason Thanks for the video. Just ran software and found my O2 post cat voltages are fine at 2500 rpm a steady 0.7 except, ever minute or so, the bank 2 graph it will take a dive for a second and then recover. Any thoughts you might have to offer? Cheers.

[@76ameer]

شكرا جزيلا على مشاركتك لنا بالمعلومات اقدر ذلك كثيرا واتمنى ان تمر هذه الفترة على خير وان تزول محنة هذا الفيروس (arabic). Thanks a lot

[@ShaneMclaughlin72]

As a new E46 owner your channel has become an invaluable resource. Thank-you! Question: What are your thoughts on aftermarket Cat's? I've read that they are a waste of time and money because they only last a few months. Given the cost of genuine parts, it's hard to avoid the aftermarket option.

[@Ivan-ry7vm]

Thank you, good informative video.

[@omarhadeed8248]

Great explanation of how the emission system works on a E46. Could you do a small video on the vacuum lines that run in the trunk which are part of the emission system. My vacuum line snapped out of place god knows when. I bought a new one and it was not too bad of a fix. I don't know if it made any difference though. I may have read somewhere that it has to with the BUTTERFLY FLAP or something? On a different note, if it makes you feel any better in FL you can renew your vehicle's registration right from home, with no smog tests ever required.

[@lexiaontube]

Awesome video !!! now i know how to test cc :) THX so much !

[@billyyoder8171]

Thank you for the video. I appreciate your videos. Have a blessed and safe day.

[@gegervary]

I've been watching many of your videos that have helped me so much over the years with my 03 e46 320i, and I want to thank you for that. However, today I have an uncommon problem that nobody can seem to solve, and I am suspecting the catalytic converters. I have rough idle issues both on cold and warm, the engine has a light and unusual growl to it, and most of the time but not always a ticking can be heard. After the engine reaches normal operating temperatures, oddly enough my clutch start to squeak, towards the very end of the pedal it doesn't feel smooth anymore, and it just gets worse the longer the car runs and is driven (brand new single-mass clutch kit, with all related components new). On cold start the clutch won't squeak until again the car is driven and is warm. No codes at all, checked for vacuum leaks, all other components have pretty much been replaced or checked, spark plugs, coils, hoses, DISA was rebuilt and the VANOS as well, cleaned throttle body, ICV, MAF. I gathered data on idle and while driving, and apparently all PIDs look good for all parameters. The only thing I noticed was that the POST-CAT sensors show oscillating voltage when the engine is being revved up. So clearly there is something wrong with the catalytics, but could it really cause my idle and clutch issues? I am suspecting that restricted catalytic converters cause turbulence near the exhaust valves causing the engine to idle rough, and once they heat up are possibly also heating up the transmission next to it more than normal temperature and thus compromising the throw-out bearing lubricant in the process. That anyway is my theory. It just drives like shit, especially in 1st gear and low speeds, clutch is hard to get along with and it shouldn't considering the mileage and the fact I've changed and maintained almost every single part I can think of. Your input on this sir would be greatly appreciated, if this of course does get to you.

[@sgtmasaru7437]

did you find a solution?

[@pochron1105]

Very informative, thanks!

[@BmwMe-uh9sy]

Great video, always wondered why my car was low on power!

[@asforme762]

Can a bad catalytic converter cause a P0171 & P0174? I have both showing. Can't seem to find a vacuum leak and Indy nearby says I need a catalytic converter.

[@BmwMe-uh9sy]

Anthony Lane nope, means systems running too lean, check the hose going to the dipstick and or get a smoke test that’s almost always what needs to be done

[@cruzzguzman]

@@asforme762 i have P0171 only... and from what i've heard it's possible that it could be the cat. For me i believe my Bank 2 cat is clogged which is causing excess air to come back into the engine causing Bank 1 to be lean. I've done a exhaust back pressure test from my Pre-Cat sensors and my bank 2 cat seems to be trashed so i believe that is my problem (low mpg -16.4mpg, stalling, engine power loss, strong exhaust smell from behind car, can't pass 45 mph when going up hill)

[@AMMA-we3zz]

@@asforme762 you have a bad DISA valve on the intake manifold. Typically, the flap is broken. Replace it or buy a repair kit and fix it assuming it still holds vacuum

[@Youtoo2128]

Good explanation. Thanks!

[@djmarkelee1]

Hi 50’sKid, great job on all the videos. I’ve managed to change lots on my 2002 316i estate. I have a new issue now, smoke from engine bay behind engine. Smells oily and loss/hesitant on power. I’ve replaced the valve cover gasket, coolant thermostat, expansion tank and I found oil in the brake booster so I have replaced that too. I haven’t yet done the CCV so that’s my next job. Any help on this would be appreciated. Thanks for your time.

[@ivanguzenko4645]

hey 50skid love your videos man, you mentored me throughout my entire manual swap project so thank you so much for that. I just got a p0420 and p0430 codes at the same time is it possible that the cats arent the issue?

[@andreiput9492]

Jason i have a similar issue with these codes and my 330ci. after the car has cruised for about 30 minutes, and a hot soak for about 20 minutes and then the light comes on when light throttle between 1500-1800rpm. i ran an extended journey and the light came on a few times but eventually did not come on at all for about 500 miles. i do not detect any vacuum leaks and performance and economy are both good. One solution I have heard is to use an O2 plug foul type spacer on the post cat sensors to remove the sensor from the direct exhaust stream which may fool the computer to not report the issue. Any ideas for a diagnosis? i do not want to replace the cats, and if I were to do that then catless headers makes more sense. Car has done 105 miles.

[@geoffreyrawlings9736]

Brilliant easy to understand.

[@regrock100]

I have the same codes on my BMW. Do you have a video on how to change the exhaust manifold?

[@irideroadbike]

Do you know if that software program that you used can also change some code. Like uero lights or something simple like door locks

[@mostwantedmotor]

Great video and fair diagnoses. But in wondering why didn't you attempt to clean the converter? Many videos have claimed to run a blended gasoline mix to help break up the build up the cats collect. I want to say they mix it with alcohol our lacquer thinner.

[@Gary_in_NoVA]

Suggest try O2 extenders (Google “O2 extender”) on the downstream sensors for P0420/P0430 codes before replacing the cats. They’re only ~$8-$10 ea. Worked for me going on 2 years, now. Worth a try.

[@monkeytarget93]

Could you show how to break down a exhaust system completely from headers to mufflars. I'm lookin to have mine replaced but I'm not sure if my 330I can actually just do a axle back exhange or if I need to buy the whole thing.

[@bdon58K]

Say, do you know if a bad secondary air pump could throw a P0420 code?

[@crazyharis]

That was the best video ever 👌

[@ewebbytrailscout]

You may want to double check on the studs, I think they are a special material to not bind with the block aluminum. I think they are a special brass stud. You may never get a steel one out.

[@iamthewelcher]

Here in 2020!!! Because I didn't have enough problems already!

[@tribewu3223]

Hey I'm wondering if you can confirm something on my data before I got ahead and buy some headers lol I bought a 03 330ci with 150k miles when I bought it like 2 months ago. With a P1349 misfire cylinder 4 with fuel cut off.. & since this day I been chasing the problem down.. I haven't replaced much but I had a e46 325i before this one so I know about all the common leaks and things that tend to go out. So after driving it like that for about 3 days (I know I shouldn't) more codes pop out and it was misfire on all cylinders with fuel cut off except 2 & 5. So I did the obvious first change plugs and coils to brand new oem ones. Clear the codes and when I started it back up it felt a little better... after about 3 min on idle the check engine light came on again.. check it again and it was still P1349 & still running like total CRAP. So I did the next, check the fuel injectors with the old screw driver trick and they all were working I even read the ohms with a meter and they were all the same numbers.. I know it's not the fuel pump cause why would only 4 be misfiring.. Plus the car runs HORRIBLE after it drops 1k rpm it starts to shake bad and when u rev it pass 4k u hear and feel hard vibrations under the car like the drive shaft it really lose or something (which I still need to inspect better) but a quick look under there and it feels fine guibo etc.. pretty sure it's not a bad idea to replace the center bearing and all those things but that's coming lol anyways I also did change the fuel filter for a Mahle one, reading on the forums I found something interesting someone with the same code as mine but he had done pretty much everything even had a brand new head in it did compression test, leak down, new injectors, etc & nothing. Till he did a back pressure test and found out that bank one had 7psi and bank two had 3 psi I believe.. I'll post the link if you want to go ahead an check it out for yourself www.bimmerforums.com/forum/showthread.php?2364925-P1349-4-misfire-with-fuel-cutoff he has the same car I do as well so I'm hoping that it and not a messed up valve or something I did the same test you did but on app called "torque" bank 1 looked normal but bank 2 was just a straight line and when I rev it to about 2-3k rpm it would start to go lower I took some screenshots to see if you can take a look at them? I can send them to your email or something.... thanks

[@TheCowgirlNiamh]

Great job Jason! youll breeze through smog now 😂

[@karlkarl5733]

Great video thanks!!!

[@gzuschrised5152]

I have these two codes but it also has one code where it detects that the sensor isnt connected or something...causing both of the other codes to pop up... any advice?

[@LINOCASTILLO]

Where did you get the used catalytic converters

[@nicebloke6066]

Hey 50skid, thanks for the video, really informative! My 190k mile 330i just gave me a p0420 on a run - I checked the O2 readings on a warm engine at 2k revs and both banks show exactly as they should (varying pre cat, 0.7 steady post cat). I noticed that the AMM clips were popped off which could have caused a slight intake leak - is it possible that that caused my code? It's not the one I'd expect, but might make sense. I would have expected both banks to be affected though... Codes reset and I will see how I go, but thank you for the O2 reading test, hopefully that means cats are ok 🤞🏻

[@markybarra8996]

Hey love the channel! Just got an e46 myself and you’ve been my go to for figuring stuff out. Currently I have a code(p2004) I was wondering if you had any idea what the problem/solution would be for this?

[@osaxchex2028]

Hey 50skid loved ur video! I believe mine are done cuz I have extremely loss of power and the eml light came on. Also check engine light and the traction light. Where did u get those used cats? I have an 2000 323i e46

[@Wednesday407]

50sKid did you feel before catalytic converter change loss of power and after change to new one good acceleration?

[@johnlindley8323]

Just changed bank 1 on my n53 330i hardest part for me was the corroded bolts and also removing the engine mount

[@besofacacia6103]

it was helpfull thanks

[@jamesellis3846]

Hiya, your videos are amazing and very detailed. Used them plenty of times! Is this the same for the 4 cylinder n42 engine? I've had a 0420 code a few times and 1168 & 1170 at the same time. Do you know what that means? Any help would be much appreciated! No one else seems to know. Cheers👍

[@jameslatimer1432]

Bro you can just put vaporized water through the inlet intake do this and will make a big difference it works 100% try it first then give car a good hard drive down the motorway !! Clean manifold pressure sensor and air flow metre turbo Boost sensor and any other senses you can get to easily

[@ThreeDimGraphics]

Any differences after the change? More "power"?

[@derekkchung]

Wide band you are talking about if it is for a 2002 E46 and upstream and downstream use the same technology. But they still have different part no.

[@felixsolis4586]

I need help lol, I just changed my o2 bank 2 sensor Nd all the other sensors are working besides 2 what did I do wrong or what am I missing? Bmw 525i 2003

[@drew2850]

Hey man I was wondering if I could contact you about this code for my e46

[@fobiojames]

I have straight pipes past the cats and it sound muffled after I put cheap coils in them. I swapped them out and it sounds better but I have a feeling they're packed with oil now... is that a possibility?

[@ronaldescoto27]

Thanks for your information very nice and helpful question I have a 1998 E36 and smoke smells really bad pls help me

[@Wednesday407]

Also what was the your mileage when you changed your catalytic converter?

[@BOUZOUKI_PETE]

changed rear cat, gas cap, purge valve, sensors, etc. check engine light still on and codes still come up

[@joelvargas5460]

I Have P0492 and P0491, will I also have to change the catalytic converter and 02 sensors, or is this just an issue with the fuel injectors?

[@diyengineerUSA]

If I have a plugged cat and it’s literally blowing out my secondary air valve and melting my plastic hose, that’s for sure a cat right? Replaced the hose and valve twice, new blower also and it does work.

[@danielhinojosa1748]

I was wondering if I could use cats from a 2002 e46 330i on a 99 e46 323i? And would it pass smog?

[@VENUEATHENS]

You're total enthusiast you need like a M-bmw

[@76rtc]

How many cats does the e46 m3 have? I just tried to get mine smogged in California and the shop told me the car only had 3 out of 4 cats and was missing one. I thought there were only 2 cats, but this shop is telling me there should be 4 and that one of mine is missing?

[@springsnetworktv5821]

I have a 2002 E46 my cat cable melted and and blew the gear fues. I disconnected the 2 cat cable and the fues is ok not it drives. Should I remove the air pump or I can just disconnect the cable to the air pump. What is going to be the effect on the car. Temperature on the average here is 28°c . It hot some time. I need an advice

[@ThreeDimGraphics]

Great movie!

[@kennyspringer7668]

I never threw these codes that you were talking about however I'm still getting lean codes or rich codes but at startup I get my E34 codes permissible range exceeded on both Banks and I get an STD black spot out of the back of my exhaust

[@tonyxu3287]

injectors

[@e46alex30]

I have a 2004 325i manual. It’s been jerky and I’m getting weird smells and the engine makes this loud sound like it’s a hot rod like a loud hollow sound. Can a bad catalytic converters be the cause of these symptoms??

[@FukRoundFindOut]

Bro, just be sure to not answer any of these questions people have asked. Super smart way to build a channel.👍👍

[@ve2430]

You kids need to hop on e46fanatics for questions

[@unL33T]

Will a clogged cat vs a burned out/broken cat read the same?

[@ryanmiller6978]

The link to the software is for a german version. Is there an option for english?

[@e90baby]

A little late but could this cause a choking engine on uphills in a manual car?

[@TedSchoenling]

Headers? or since you are in CA you can't do that?

[@muzzac1545]

My 325ci threw the p0420 code which i believe is bank 1. So i graphed the sensors like in the video and bank 1 looks fine, but bank 2 is showing the signs of a bad cat. Confused.

[@busterscrugs]

My brother's 08 Lexus IS250 threw a P0420 because of a tiny exhaust leak (small crack in the piping right before the catalytic converter on bank 1). Welded a bead over it, cleared the code, never came back. That being said, my family's 15 Forester XT threw a P0420 and it needed a new cat, thankfully under warranty (only 49k miles). Also, do you believe the school of thought that says if your cat goes bad it's because something is wrong with your engine (i.e. oil burning, rich/lean condition, misfiring, etc) which caused the cat to burn out? And lastly, that CA state smog test is a joke lol I could pass that test in my E39 530i with headers (catless) and tune that got rid of the CEL and secondary O2... Same story with my RSX Type S with a Hondata, header, cat delete, and secondary O2 delete, both cars have the emissions monitors set despite having no cats.

[@arnolduk123]

The M54 6 cylinder engines have wideband O2 sensors upstream and narrowband O2 sensors downstream, operate differently so cant swap them around.

[@JuarezRichard]

Just bought a 2001 330i and I noticed the catalytic converters smell pretty bad when I push the engine. Car has 171k miles what would be your suggestion to diagnose the Issue? Thanks!!!

[@ve2430]

How do you know if the o2 sensors are good and telling the truth?

[@Naphewonix]

Hello Sir, hope you see this. Is it possible to explain what are the effects of a bad cat on fuel consumption and engine performance? Additionally, what's the effects of removing the Cat without deleting it from the ecu on fuel consumption and engine life/performance. Finally, what is the effects of cat delete on fuel consumption and engine life/performance.

[@philipgrobler7253]

How does a decat work on these cars?

[@ianmatterson5632]

hi 50's, how did you discover the port number?

[@Nateclrk]

50skid Do you suppose a cat could be bad if they dont heat up to the same temps from idle? I.E B1S2 .72v B2S2 .68v (slower misfiring bank at 5000rpm)

[@delorenzobrand9715]

Aye I gotta question about the battery , my uncle thought he knew Wht he was doing n took out tht yellow pice in the two wires tht Connect to the battery do tht matters ? Cause my car lights still come on n everything but idk if it’s making it get a less charge or something could you replace tht ?

[@gianfrancoa]

Delorenzo Brand writing with all the letters would make your problem easier to understand

[@delorenzobrand9715]

You know stuff about bmws ?

[@brianlexl1215]

can a vacuum leak cause a catalytic code? For instance, I did a smoke test and it was leaking by the intake air duct and underneath the manifold. Im guessing the oil separator and the hose will need replacement as well.

[@brianlexl1215]

I also had a misfire in cylinder 1 code, but I just had all new spark plugs and coil packs put on so Im hoping fixing the leak will erase these codes.

[@spawnlawn9754]

I am getting ready to do this job. Bank one 0420 and bank two 0430. Can it be done in driveway on ramps or jack stands? Very mechanically inclined, have all the tools, just can’t get the car very high in the air.

[@kennethmoriarty3201]

I did this job last year, new magnaflow cat headers. I did O2 sensors,tuneup, the Vanos solenoids, the oil non-return bslves, DISA Valves, smoke tested intake, you nam it. Car still got these 2 codes but much less frequently until this last couple of months, now coming back within 1 days of resetting & cant pass emissions insp here in NY. where do I go with this? Car otherwise runs like a top no misfires, no other codes, steady idle, all good.

[@rb4280]

hey Im having this issue on my 2000 328ci where the catalyst monitor is not ready n is showing my downstream sensors are fluctuating like yours but im not getting any codes or stored codes, Catalytic converters are expensive here in cali so thats my last option u got any suggestions? i'd appreciate it

[@50sKid]

Nah if your downstreams are not steady, it’s definitive. You need new cats. I bought some used low mileage ones off eBay and it worked out. Good luck!

[@bardhiseni1301]

​@@50sKidThank you for the video. I made just right now a test and a made a video. I think my cats are working. kzbin.info/www/bejne/opPTk3x_hrNqnNUsi=-dLxlOMrATvvVTVS

[@Tokyodrift5000]

I've been having an issue recently where my CEL came on and code was P0430 (Catalyst below efficiency bank 2). Checked live values and the value for bank 2 post cat was reading steady between 0.6v and 0.7v (So no issue here?) Both pre cats oscillate as normal too so what could be the issue here? Experience no power loss either and engine is as smooth as can be

[@nicebloke6066]

Did you get to the bottom of this? I have a p0420 and o2 sensor readings checked out. Did find my AMM wasn't clipped on properly though.

[@Tokyodrift5000]

@@nicebloke6066 nope, still haven't solved it. I've taken the plunge and bought 2 precat sensors as I assume the originals are still on the car (103k miles). I'm hoping it's just a sensor that has fallen out of spec over time hence the codes. No vac leaks as far as I can tell and MPG is normal

[@stevenfierro5439]

I have a 2003 e39 that gets an intermittent all 4 O2 sensors heaters shorted to negative. The fault comes up during a scan as not present at the time but it is always there and I can never clear it. I have measured all 4 heaters at about 2.5 omhs and the voltage across all 4 does pulse on and off when the car is running as should. Do you have any idea what it could be?

[@50sKid]

Sounds like a problem with the DME (engine computer). Seek professional help on that one

[@elvinnovruzov5775]

Does it affect how the engine works? cause my e46 does jump around while driving but on idle it stays at 0.7-0.8v. I wonder if it is what makes it jerky. As always very informative, thank you so much.

[@mjc2094]

Clogged cats will impact performance, yes.

[@vosedon]

Your good you.

[@paulasencio2924]

I been having a P1092 and I can't find the problem is 2004 bmw x5. 3.0 Any suggestions???

[@souleymanebadini1783]

Can bad catalytics converters cause a high consumption of fuel?

[@uNabL3]

My Mazda 6 2.0 (2007) has an upstream wideband O2 sensor (AFR) and a regular downstream narrowband O2 sensor (I believe). A few things I'm worried about: 1) I cannot check the AFR sensor since it has no voltage output (only current) - in ELM327 ScanMaster at least; 2) the voltage on the downstream sensor is constantly low - it stays at around 100-150mV. O2 sensor temperature is around 300 degrees C. If I step on the gas the voltage drops to essentially zero. And I've never seen it going above 0.3V (or even 0.2V). At the same time, STFT and LTFT go negative. This is all at idle - haven't taken it for a test drive yet. I wonder what could be my problem there. :/ No fault codes or anything, just rough idle. Sometimes when I let off the gas the RPM drop below 600. At the same time, it is not surging or anything. Thanks a lot.

[@50sKid]

It’s harder to diagnose an A/F sensor with just an ELM327 adapter. www.underhoodservice.com/troubleshooting-wideband-o2-sensors/ you’re right in that your downstream sensor is narrow band. There is no need for a more expensive narrow band there. that being said, it does sound like your downstream sensor isn’t operating correctly, particularly the temperature (should be at least 600 degrees). What does the upstream current read as?

[@Throughthelurkingglass]

Don't clean your 1st set of o2 sensors if one of the cats is clogged, running almost as bad as when a leaky inector made my intake manifold explode last year, Imma try to clean it, if not, im in Texas no more inspections, I'll run headers and make it shoot flames🔥.

[@brancook1223]

So is it safe to drive with a bad cat converter?