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So, I was driving my car today.. and after about 60miles, my CEL came on. So i pulled over and did the paper-clip trick and it flashed code 67. Upon looking online, I find the definition as:
" P0420


67


Catalyst System Efficiency Below Threshold "


.... Now, what does that mean, in english? Heh.. Any ideas would be appreciated.
 

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do u have a high-flow catalytic converter??

if u dont have it, it probably ur O2 sensor have gone bad or ur cat have gone bad. i would replace either both of them. u can remove the cat and inspect it.

we need more information. wat kind of car do u drive? header/cat??
 

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All that code means is your 2nd 02 sensor isn't seeing enough oxygen increase from what it is seeing at the 1st 02. There for the computer thinks your cat is not working properly and/or is missing or gutted. You can just buy a MIL eliminator if you did get rid of your cat, it will plug in where your 2nd 02 plugs in and you won't get anymore CEL's from it.
 

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Yeah, I guess a little back-history would be nice, eh?
Car: 1996 Teg LS, Automatic tranny. Stock, besides a SRI and muffler.

I noticed something rattling, sounded a bit like a heatshield, when i'd rev to about 2-3k. Under WOT it would go away, but when just tapping the throttle, you could hear it rattle. Long story short, I took the cat off and the filter/honeycomb (whatever you want to call it) was near non-existant, only about the size of a elongated baseball or so. That was the cause of my rattling noise, so I just punched out the filter and hooked the cat back up.

The O2 sensor did look a bit used etc, so it could probably due with replacing. Thanks for the replies, its appreciated.

*EDIT* sorry, I posted the original thread from someone else's account.
 

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If you replace that 02 sensor sfter your cat that you gutted you are chasing your own tail, you know kinda like a dog does. It will still set that code with a new sensor. Just buy a MIL eliminator from jegs or just deal with the CEL. All that sensor does is see if the cats doing its job. It will not effect the was your car runs like the 1st 02 sensor will.
 

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I can deal with the CEL being on.. And i figured it was because I gutted the cat as well. Just wanted to ask and make sure that's what it was. Like I said, the light came on after 60miles and I still had 250mi left to drive.. didnt want to hurt anything.
 

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Its hard to get away with that on obdII cars, being that your cat is gutted it dont help. Your running lean, if you think that It helps your car run faster your mistaken. No cat equal's high hc meaning mil on, ecu thinks your runniing rich so it leans the fuel trim to compensate. Shouldnt have gutted your cat, if you were going to go that route you should have bought a $20 test pipe and saved your cat for inspection. Now you got to replace the cat which is more expensive.
 

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Ok then, If your 02 after cat thinks your running rich and is leaning your car out then i wonder what the 1st 02 before the cat is doing when it sees the mixture go lean, maybe its just there for looks??. Thats why there is two of them on OBD2 the second one has one simple job, turn the check engine light if it determines the cat is not working properly. Do you really think they would make they one after the cat control fuel mixture? Nope, And 9 of the lab teachers I have been through who have been working on cars sence before I was born think so to. But you never know I could be wrong, they could be wrong, he could be right. Its just from what I know about OBD2 and what a cat does it just makes sense to have the first 02 worry about the a/f ratio. Lets look back at OBD1, 1 sensor before the cat.
 

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ATISTANG said:
Ok then, If your 02 after cat thinks your running rich and is leaning your car out then i wonder what the 1st 02 before the cat is doing when it sees the mixture go lean, maybe its just there for looks??. Thats why there is two of them on OBD2 the second one has one simple job, turn the check engine light if it determines the cat is not working properly. Do you really think they would make they one after the cat control fuel mixture? Nope, And 9 of the lab teachers I have been through who have been working on cars sence before I was born think so to. But you never know I could be wrong, they could be wrong, he could be right. Its just from what I know about OBD2 and what a cat does it just makes sense to have the first 02 worry about the a/f ratio. Lets look back at OBD1, 1 sensor before the cat.
Think ping pong......back and forth back and forth. This is what I was taught, If i remember correctly cuz I spent a lot of time daydreaming in class. First sensor reads wats going in , second measures amount being processed. All those two sensors do is compare and adjust, compare and adjust. I wont get into any arguements about this cuz everyone was taught differently. Secondary o2 sensor does tell you if the cat is working properly, but when I diagnois at Toyota, which has a more complicated emissions system than honda, Any time I get a cat below efficiency code, I sell a rear o2 sensor first. Why, Cuz 8 out of 10 times its a lazy or bad o2. Very rare that a cat will go bad. The main purpose of the secondary o2 sensor is to measure hc readings and keep track on that cat. Yes, the primary o2 sensor is important, but it can't do its job with out some readings from the rear o2. The reason why any obdII system will lean out the fuel trim is because hc readings are more important to the government, they dont want the car to be spitting raw hc's into the air.
 

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If you would have read my post, I said I gutted the cat because the filter was nearly non-existant. It wasnt really doing its job. I wasnt doing it to gain performance. It was rattling and making the car sound like shit. I was only asking because there are specific codes for each O2 sensor that can be thrown, and since it wasnt either of those codes in this case, I was curious as to an answer. And there is no emission/inspection where I live, so that's not an issue.
 

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Dang Civic said:
Think ping pong......back and forth back and forth. This is what I was taught, If i remember correctly cuz I spent a lot of time daydreaming in class. First sensor reads wats going in , second measures amount being processed. All those two sensors do is compare and adjust, compare and adjust.
Yes you did to much daydreaming lol, each senor switches back and forth from 0-1v constently. Ok, 02 eliminators to do away with your 2nd 02. People use them all the time on cars making anywhere from 100hp to 1000hp. Do you ever see anyone running eliminators for both primary and secondary 02's? Hmm... I wonder why not. Can anyone answer this question? Anyone.... Anyone.... Bueller?? Lets see here, eliminators simulate a secondary 02 that is seeing something cleaner than what the primary is seeing. There for, these are designed to switch back and forth very fast and stay towards the low end of the voltage range, this tells the ecm "cat is working great" (for those of you now confused it doesn't literally say that) even though the cat might now be laying in your garage in that pile of stock car parts you could probably build another car with. Thats what they do, they fool the ecm, not something you would do if it had anything to do with you a/f ratio, at least I would hope not. If you did do this your car would always run rich do to the signal it is sending. What if it was made to switch back and forth to where it looked like the car was running at a a/f of 14.7, you ask? Your ecm would freak out :whore when it made a change in injector duty cycle, ign timing, egr valve % open, or stuff like that because it should see a little change from the primary 02, and when it doesn't you get everyone favorite light, the CHECK ENGINE LIGHT :eek . I know this because in lab we would get bored, so my teacher (who is some kind of driveablity god) would set stuff like this up on a lab car then turn us loose. Then when we would find the problem and fix it he would make us explain the whole process from how the problem started, what else did this problem effect, to how the ecm reconized the problem. If anyone of you obd2 guys out there have a real wide band 02 (not the one you splice into your primary 02 sensor just so the gauge can tell you that your 02 is infact switching back and forth like it should), get your car to operation temp and look at your a/f then with the car still running unplug your secondary 02 and see if it changes.
 

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ATISTANG said:
Yes you did to much daydreaming lol, each senor switches back and forth from 0-1v constently. Ok, 02 eliminators to do away with your 2nd 02. People use them all the time on cars making anywhere from 100hp to 1000hp. Do you ever see anyone running eliminators for both primary and secondary 02's? Hmm... I wonder why not. Can anyone answer this question? Anyone.... Anyone.... Bueller?? Lets see here, eliminators simulate a secondary 02 that is seeing something cleaner than what the primary is seeing. There for, these are designed to switch back and forth very fast and stay towards the low end of the voltage range, this tells the ecm "cat is working great" (for those of you now confused it doesn't literally say that) even though the cat might now be laying in your garage in that pile of stock car parts you could probably build another car with. Thats what they do, they fool the ecm, not something you would do if it had anything to do with you a/f ratio, at least I would hope not. If you did do this your car would always run rich do to the signal it is sending. What if it was made to switch back and forth to where it looked like the car was running at a a/f of 14.7, you ask? Your ecm would freak out :whore when it made a change in injector duty cycle, ign timing, egr valve % open, or stuff like that because it should see a little change from the primary 02, and when it doesn't you get everyone favorite light, the CHECK ENGINE LIGHT :eek . I know this because in lab we would get bored, so my teacher (who is some kind of driveablity god) would set stuff like this up on a lab car then turn us loose. Then when we would find the problem and fix it he would make us explain the whole process from how the problem started, what else did this problem effect, to how the ecm reconized the problem. If anyone of you obd2 guys out there have a real wide band 02 (not the one you splice into your primary 02 sensor just so the gauge can tell you that your 02 is infact switching back and forth like it should), get your car to operation temp and look at your a/f then with the car still running unplug your secondary 02 and see if it changes.
:bow
 

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Did I say anything out of what I meant?

This is taken from my Toyota book, written by Toyota.

" OBDII vehicles require two oxygen sensors: One before and after the catalytic converter. The Oxygen sensor, or air/fuel ratio sensor, before the cat. con. is used by the ecm to adjust the air/fuel ratio.....The oxygen sensor after the cat is used primarily to determine cat. conv. efficiency."

Just a little bit from the book. What I said is one of the basic priciples of what I was trying to explain. Maybe I was a bit unclear, but still, I was not completely wrong nor you. There is also an adjustment chart that any obdII ecm will follow too. It explains the rich and lean status. Shall I scan and post that too? I never said you were wrong buddy, but you take my opinion as if I also didnt know what i was talking about. I some times write as if I am confused but I talk a whole lot better in person.
 

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Dang Civic said:
Your running lean, if you think that It helps your car run faster your mistaken. No cat equal's high hc meaning mil on, ecu thinks your runniing rich so it leans the fuel trim to compensate.
This was what is wrong, the rest is pretty good, sorry about being a smart ass, thats just how I am sometimes. I think I drank to much coffee before wirteing that :bounce
 
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