bgambino Posted November 28, 2009 Share Posted November 28, 2009 so I traveled an hour and a half to buy a mint 96 legacy front bumper plus grill and both head lights for $100..great deal I end up finding out that this guy is a sub tech So I ask him (among other things) about the P0420 and if many times the O2 sensor is the real culprit He says no The proof he says is that at the dealership he works at...they will replace the cat and REUSE the original O2 sensor....and no more code tripping It actually shocked me that a dealer would not go for the extra bucks and sell the O2 sensor to the sucker (I mean "customer" of course...LOL) so this seems strange to what I have read hear with the experiences of others thoughts? Link to comment Share on other sites More sharing options...
frag Posted November 28, 2009 Share Posted November 28, 2009 What if they made more profit replacing the cat than the sensor... Just a tought. Link to comment Share on other sites More sharing options...
johnceggleston Posted November 28, 2009 Share Posted November 28, 2009 for the longest time i have been a member of the "it's the o2 sensor, dummy" crowd. there seems to be good evidence to support that school of thought. folks with a p0420 replace the front o2 sensor and the problem goes away. but of course there are those who SWEAR that it is the cat and it should be changed out. and there are those who have replaced the o2 and the problem persist. i guess it is possible that neither the cat nor the o2 sensor work as well as they did when new and that replacing either one improves the over all performance (in some cases) which eliminates the code. just a thought, but sensors are 100$ and cats are several hundred more, i'm staying with the o2 crowd for now. Link to comment Share on other sites More sharing options...
Hondasucks Posted November 29, 2009 Share Posted November 29, 2009 Most of the time at my work we will give the customer the option of replacing the sensors, since sometimes it is the sensor. What I will do is plug in the laptop and drive the car and watch the sensor readings, and if the rear sensor seems to be reading a bit sluggish, I will recommend replacing it. I've only had that happen on one car so far though, but it was almost a year ago and he hasn't come back for a cat yet! My dad's Outback had a P0420 and it has a brand new cat in it, but they are aftermarket and I think they're just not quite what the computer is expecting so it's throwing a code for it. It is important though that the shop/dealer plug in the scan tool and watch the data for both 02 sensors to make sure that the problem is in fact the cat, instead of throwing one in there. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 29, 2009 Share Posted November 29, 2009 Spark plug non-fouler between the 2nd O2 and the cat. No more cat code. Yes I have done it. GD Link to comment Share on other sites More sharing options...
Qman Posted November 29, 2009 Share Posted November 29, 2009 Spark plug non-fouler between the 2nd O2 and the cat. No more cat code. Yes I have done it. GD Simply a bandaid and should not be recommended as a plausible repair. Link to comment Share on other sites More sharing options...
Qman Posted November 29, 2009 Share Posted November 29, 2009 Most of the time at my work we will give the customer the option of replacing the sensors, since sometimes it is the sensor. What I will do is plug in the laptop and drive the car and watch the sensor readings, and if the rear sensor seems to be reading a bit sluggish, I will recommend replacing it. I've only had that happen on one car so far though, but it was almost a year ago and he hasn't come back for a cat yet! My dad's Outback had a P0420 and it has a brand new cat in it, but they are aftermarket and I think they're just not quite what the computer is expecting so it's throwing a code for it. It is important though that the shop/dealer plug in the scan tool and watch the data for both 02 sensors to make sure that the problem is in fact the cat, instead of throwing one in there. Great advice Andrew! Link to comment Share on other sites More sharing options...
idosubaru Posted November 29, 2009 Share Posted November 29, 2009 Simply a bandaid and should not be recommended as a plausible repair. Is there any evidence or information on this? I was reading about this on another forum earlier today and was wondering since it seems to be fairly successful. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 29, 2009 Share Posted November 29, 2009 There's a rig out in front of my house that had the cat burned out of it because of a naughty ignition coil (it's not a Subaru - it's a 2000 model OBD-II car though). I put a non-fouler on it 50k miles back. Still no code. All it does is move the 2nd O2 out of the exhaust stream. The ECU is simply looking for a percentage difference between the 2 sensors - it can't use the 2nd sensor for anything but checking the cat because *after* the cat there is no useful information to be gathered by checking the mixture (the cat just destroyed the information). You give the #2 O2 sensor the drop it's looking for and all is right with the world again. I don't see how this is a band-aid as it's a permanent fix.... if you mean it's bypassing the emissions controls well then yes it is but I don't consider gutting a cat to be a band-aid..... that's FIXED IMO. Not everyone has the extra mojo in their piggy bank for a new header..... GD Link to comment Share on other sites More sharing options...
idosubaru Posted November 29, 2009 Share Posted November 29, 2009 (edited) A confusing part of this dilemna is the folks, like over on the outback boards (and probably here) that have replaced the cats and O2 sensors and still have the check engine light on. that has to be terribly frustrating to hand a dealer or mechanic that kind of loot and still not have the problem fixed. some folks can't afford that, particularly considering some of these cars are getting old and not worth much, so a $10 fix seems like a really good fit for some people. I had the O2 sensor code a while back, replaced them with Subaru units in my 02 OBW and still have the O2 sensor code even after clearing a few times. I guess it's the cats but I've seen a few threads where folks have replaced those too with no results so I'm wondering if it will fix mine. O2's I didn't mind since they were likely old, but the cat gains me nothing over the long term and all my 20 year old Subaru's have the originals so it seems funny to replace the O2 with lower miles! I'll likely try this fix before swapping cats unless I can find some quantifiable information on this whole deal. Endwrench have any info on this? Edited November 29, 2009 by grossgary Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 29, 2009 Share Posted November 29, 2009 Gary - seriously try the non-fouler. It might just save you some coin. What do you really have to lose? I don't know what Ken's objection is but I've done it and seen it work - plus the theory is sound. GD Link to comment Share on other sites More sharing options...
Qman Posted November 29, 2009 Share Posted November 29, 2009 Gary - seriously try the non-fouler. It might just save you some coin. What do you really have to lose? I don't know what Ken's objection is but I've done it and seen it work - plus the theory is sound. GD All you are doing is removing the 2nd O2 from the system. It now appears that the cat is working correctly. Which it isn't. You won't get the code any more. But the problem still exsists. You have fixed nothing. My objection is that it is illegal. In any state that has an inspection it can result in a fine. It is fine that you do it. But, you can not tell someone to do that as the correct fix. That is why I see it as a band-aid. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 29, 2009 Share Posted November 29, 2009 (edited) You are 100% correct Ken. I am in no way promoting that anyone here break the law. That said, I don't think it's illegal if there's no inspection or testing where you live - that applies to some members here. There has to be a fine and someone to enforce said fine before something is *actually* illegal. Though it's probably illegal on paper in some places that don't test/inspect..... but I digress. As for where I live - I haven't run across an inspector smart or thorough enough to catch such a thing. And if I suspected there were such a person I would obscure the O2 sensor with a "heat sheild" of my own fabrication. Such are my mad skillz. . I'm a very, very bad man and a reprehensible example to my peers. I hereby instruct all readers of this thread to shun me..... no really - you should definitely shun me. But again - NO ONE should do this - Everyone got that? (I think it's pretty clear that this is not a "by the book" repair - I didn't intent to sugest that with my prior posts. It's in the same vien as replacing the EGR and Purge solenoid's with resistors and pulling EGR's off and blocking them......). Also - if you wanted to retain a working cat then this could still be very useful. You could add a $50 ebay cat to the mid-pipe and then the spark plug nonfouler would only serve to eliminate the pesky CEL. GD Edited November 29, 2009 by GeneralDisorder Link to comment Share on other sites More sharing options...
idosubaru Posted November 29, 2009 Share Posted November 29, 2009 With the exception of CA () there might be some areas where folks don't know that "laws" are ambiguous, guess they need to know that. If I lived in a different state l wouldn't worry about it, back in MD they would just say "go fix that, then come back". It's not like they'd call the police, you just don't get passed. This idea has been discussed before here and elsewhere, different folks have different modis operandi. It's also illegal to sell used converters but that's done on every automotive forum I've ever been on. Nice one GD, that was funny. Link to comment Share on other sites More sharing options...
frag Posted November 29, 2009 Share Posted November 29, 2009 Aside from the legal problem, if the O2 sensor is installed a few millimeters back of where it shoud normaly be, it is certaineley removed from the direct exhaust flow, but is'nt it still able to "sniff" the mixture and make a relatively close call on what's happening ? Just curious, cause my second O2 sensor is installed just like that cause the original threads were ruined (dont ask me how). Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 29, 2009 Share Posted November 29, 2009 (edited) The non-fouler pulls the sensor out of the exhaust stream by more than a few mm's. It's more like 1" or so really. The probe is completely inside the non-fouler. Yes it's going to sniff *something* but that something will be much leaner than it was before. I have read that this will work with NO cat, not just a bad one. Haven't tried that myself but this "trick" is used by people who install "race" exhaust's on cars that don't see the street and thus require no cat(s). If you have just welded an O2 bung on the pipe that adds a few mm's I don't think you would affect the operation of the O2 as long as the sensor is still in the exhaust stream. I've installed plenty of mixture control O2's for FI swaps into pipe's in that same way and they work fine. GD Edited November 29, 2009 by GeneralDisorder Link to comment Share on other sites More sharing options...
Qman Posted November 29, 2009 Share Posted November 29, 2009 You are 100% correct Ken. I am in no way promoting that anyone here break the law. That said, I don't think it's illegal if there's no inspection or testing where you live - that applies to some members here. There has to be a fine and someone to enforce said fine before something is *actually* illegal. Though it's probably illegal on paper in some places that don't test/inspect..... but I digress. As for where I live - I haven't run across an inspector smart or thorough enough to catch such a thing. And if I suspected there were such a person I would obscure the O2 sensor with a "heat sheild" of my own fabrication. Such are my mad skillz. . I'm a very, very bad man and a reprehensible example to my peers. I hereby instruct all readers of this thread to shun me..... no really - you should definitely shun me. But again - NO ONE should do this - Everyone got that? (I think it's pretty clear that this is not a "by the book" repair - I didn't intent to sugest that with my prior posts. It's in the same vien as replacing the EGR and Purge solenoid's with resistors and pulling EGR's off and blocking them......). Also - if you wanted to retain a working cat then this could still be very useful. You could add a $50 ebay cat to the mid-pipe and then the spark plug nonfouler would only serve to eliminate the pesky CEL. GD Why must you always go one step too far? I mean really? My point was not that you are a "bad" man. My point was not that it does eliminate the problem. My point was simply that it is wrong and does not "fix" the problem. Frag, your O2 sensor is still in the system. Correct depth and sitting in the exhaust stream. Doing it's job as designed and required. You can laugh about it but the fact is any modification can be fined. It doesn't take a LEO to fine you. I would hope that you are not that naive. I am also not saying that I am above such mods. Simply that it is wrong. It amazes me(it shouldn't by now) that the same ones keep showing up. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 29, 2009 Share Posted November 29, 2009 My point was not that you are a "bad" man. My point was not that it does eliminate the problem. My point was simply that it is wrong and does not "fix" the problem. I know - I was only joking. GD Link to comment Share on other sites More sharing options...
idosubaru Posted November 29, 2009 Share Posted November 29, 2009 agreed Q - disclaimers important, that's funny you said you're not above some type of mods. Link to comment Share on other sites More sharing options...
Qman Posted November 29, 2009 Share Posted November 29, 2009 agreed Q - disclaimers important, that's funny you said you're not above some type of mods. True, very funny depending on the context. Link to comment Share on other sites More sharing options...
subaru360 Posted November 29, 2009 Share Posted November 29, 2009 Replacing O2 sensors has never fixed a 420 code for me. Antifoulers have fixed it 9 times out of 10. It's almost always bad cats. Aftermarket cats will not fix a 420 code. New dealer cats will, but who spends $1000 on cats for a $2000 car? Link to comment Share on other sites More sharing options...
ShawnW Posted November 30, 2009 Share Posted November 30, 2009 There is absolutely no way you can say aftermarket cats don't fix the problem. Not all cats have the same amount of precious metals and such but some have to be as good as the genuine part. I replaced my wifes cat on her Baja before trading it in and we got 8K miles without the code before trading it with an aftermarket cat and reuse of 180K mile sensors. I recently quit my job as a tech at a dealership and replaced lots of cat pipes for the 420 code with no comebacks. Im not saying that the sensors shouldn't be replaced but I got away with not replacing them. There also can be more to it than this as well. Previous damage done by blown head gaskets, exhaust leaks, poor valve adjustment, bad spark plugs, loose airbox, and other things make the 420 code come on as well. I fixed 3 by properly securing the air filter box after air filter replacement done by people that can't seem to get the tabs in at the bottom. Proper diagnosis is key. The Select monitor tells you the numbers and you can tell what is bad with it. It may be worth it to have diagnosed by the dealership at a minimum. Link to comment Share on other sites More sharing options...
RAYJAY Posted November 30, 2009 Share Posted November 30, 2009 Gary - seriously try the non-fouler. It might just save you some coin. What do you really have to lose? I don't know what Ken's objection is but I've done it and seen it work - plus the theory is sound. GD done it on my 04 gt 20,000 mile ago, not a problem in the world and the 2004 gt have the Cali emissions on it converters are high $$$$$$$$$ Jeff Link to comment Share on other sites More sharing options...
bulwnkl Posted November 30, 2009 Share Posted November 30, 2009 Ignorant question: What's this "non-fouler?" Aside: I am aware that it's against federal regs to tamper with or alter emissions-control systems. I don't have any code that I'm trying to correct, and frankly I prefer emission-controlled vehicles. I'm just curious about this. Link to comment Share on other sites More sharing options...
GeneralDisorder Posted November 30, 2009 Share Posted November 30, 2009 It's a spacer designed to keep a spark plug from being oil-contaminated by an engine that has very bad oil consumption. It just so happens that O2 sensors and spark plugs share the same thread. They are about $5 to $10 at most auto-parts stores. Look in the "HELP!" section as they are generally carried there. They can also be found on ebay. GD Link to comment Share on other sites More sharing options...
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