how i fixed my F***ing 420 code

[GeneralDisorder]

Might just un-piggy back it and try it that way. May give it just enough variation to not throw the post-cat fuel trim code.

 

GD

[the3rsss]

When anybody starts talking about an "easy" fix that involves welding my eyes kinda glass over.Anyway, dont want to hijack the thread but here is my question....I did the non-fouler trick about 5k ago. The 420 code went and didnt come back. Im in nj and due for inspection soon, I noticed they use a mirror at the state insp station. Are they just looking for cats under there? Any chance they will see the spacer? I would take it out before insp but wont that throw a pending code?

[idosubaru]

they should be just looking for a cat. that doesn't mean if they see something else they might not check into it further, but i would think that's really rare. never heard of anyone having an issue with this fix on other forums.

[CNY_Dave]

Tape a nudie centerfold under there... they won't even remember to check for the cat!

[davebugs]

As long as the non-fouler's are rusty they are kinda up out of the way and heat shield helps hide them.

 

Now if they are spiffy new shiny ones like you fixed it the day before - well, that they may actually pick up on. But I doubt it.

[J A Blazer]

For my 2000 4-cyl OBW, can someone please confirm that the AutoZone part that I need is a p/n 42009? It was out of stock and they have ordered one. I believe that it will be an 18 mm, but not sure. TIA.

[xbeerd]

i had the non foulers on my 2000 outback, i cant verify the part number as i had a buddy pick them up but the 18mm ones are the ones i had.

 

we went thru emissions 2 times (we test every other year here in WI) with them in there and never did anyone say a word about them.

 

actually the 2nd time thru they just plugged in the obd2 and that was it. no sniffer or anything

[J A Blazer]

Anyone in Virginia with experience on this issue? Here, they snif every two years and I'm due for an emissions inspection next month.

[fixingrusinc83]

check ohm resistence on plug wires. Read every poston it and everyone says O2 note new O2 in new Cat did not solve one guys post

Engineers At FUJI would have had this problem out of factory but did not. I will bet most is ohms above 5 when new plug wire is .7 to .8 (same amount of gas in but cold spark vrs hot spark gives less out to allow CAT to burn efficently)

[tanderson22]

When you get a P0420 code, it is because the cat is not getting the correct fluctuation in exhaust gasses (lean to rich & back) to work. It is a mixture problem and no matter how you fool the computer or how you get the light out, there is a problem that needs to be corrected. You can replace all the 02 sensors you want, most likely the o2 sensor is working and picking up on a problem, like 95% of the time a code for an o2 sensor is.

 

If you think you can attack this problem without A) knowing the 5 critical inputs understanding the OBDII / IM240 programs, your in for a ride.

 

The only thing I can say for sure is I have an extensive emissions background and I didn't read a post here that sounds like anyone has the foggiest......

[tanderson22]

check ohm resistence on plug wires. Read every poston it and everyone says O2 note new O2 in new Cat did not solve one guys post

Engineers At FUJI would have had this problem out of factory but did not. I will bet most is ohms above 5 when new plug wire is .7 to .8 (same amount of gas in but cold spark vrs hot spark gives less out to allow CAT to burn efficently)

 

What are you smoking????? Spark Temperature??? OHM resistance checks are a waste of time in most any repair scenario. The whole suppression ignition system is based on high voltage discharge through high resistance... The simple test there would be.... is it misfiring??? Yes, or NO???

 

And, no a new cat will not fix any P0420 problem unless the problem already took that cat out, and the new one will soon follow suit, because only the problem and not the cause was fixed.

[tanderson22]

18mm non fouler.

 

Yeah - just do all three.

 

And yes you are making this way too complicated.

 

1. Drill through the non-fouler with a 1/2" bit.

 

2. Unscrew sensor(s) using an open-end wrench, Ford wrench, crescent, etc

 

3. Thread sensor into non-fouler.

 

4. Thread the assembly back into the exhaust and tighten.

 

Done. Takes about 15 minutes.

 

GD

 

 

 

- Stupid Idea. Does nothing. just putting a "shield" over the o2 sensor so it's not in the flow of the exhaust. Poor idea built from misconceptions of how an emission system works.

[tanderson22]

The reason for blocking the rear sensor is that the ECU looks for a change in voltage at the rear sensor compared to the front sensor. The change in voltage is reflective of the change in oxygen content in the exhaust after the catalytic converter does it's work. It has to see a lower voltage reading from the rear sensor in order to determine that the cat is working properly. Removing or partially removing the rear sensor from the exhaust stream effectively lowers (or is it raises... I can't ever remember which way that goes ) the voltage that the sensor sends back to the ECU, which tricks it into thinking the cat is working well, even if it's not there.

 

I can't say exactly why the code hasn't come back, but it very well could have something to do with the blockage of the front sensor.

 

 

Now that's interesting. They must have had the same idea you had. Or is there where you got your inspiration?

Either way. It seems to have worked for you, consequences yet to be seen, hopefully it lasts.

 

- ALMOST right..... a rear O2 sensor looks for stochiometricy from the converter - indicating a complete combustion/catlization, and it looks for 14.7 or about 0.5 volts in a short band (0-1.0v) sensor and DOES NOT FLUCTUATE when the cat is working.

 

Putting the O2 sensor in a sleeve or non-fouler can mimic this condition; however; you have a mixture problem somewhere else, and you will pay for it either in fuel or damage to the motor.

 

You compound your problem by "moding' your rear o2 because the computer will always have erronious fuel trim information because it "thinks" the cat / mixture is fine. Like every computer, garbage in, garbage out, and you will see the results when you have to rebuild your motor, or why you can't seem to get it to run "just" right anymore....because the fuel trim matrix is packed with erronious information because you fooled the computer, and the correct mixture is never output.

 

You have to find the cause of the mixture inefficency, fix it, and then you will have a real repair.

[CNY_Dave]

When you get a P0420 code, it is because the cat is not getting the correct fluctuation in exhaust gasses (lean to rich & back) to work. It is a mixture problem and no matter how you fool the computer or how you get the light out, there is a problem that needs to be corrected. You can replace all the 02 sensors you want, most likely the o2 sensor is working and picking up on a problem, like 95% of the time a code for an o2 sensor is.

 

If you think you can attack this problem without A) knowing the 5 critical inputs understanding the OBDII / IM240 programs, your in for a ride.

 

The only thing I can say for sure is I have an extensive emissions background and I didn't read a post here that sounds like anyone has the foggiest......

 

 

P0420 indicates that the after-converter O2 sensor is not seeing enough of a difference in reading from the before-converter O2 sensor, that the catalytic converter did not consume as much oxygen as expected, nothing more and nothing less.

 

One of the causes could possibly be a lean/rich mixture problem (other than a small vacuum leak), but you would most likely get a code based on the failure of the computer to obtain the correct mixture.

 

 

Dave

[CNY_Dave]

- Stupid Idea. Does nothing. just putting a "shield" over the o2 sensor so it's not in the flow of the exhaust. Poor idea built from misconceptions of how an emission system works.

 

I think you are the one with a misconception about the way the system works, although I agree that this method is only a last resort in cases where it's a too-sensitive system and checks have been made for legitimate problems (or, the cat just plain doesn't work and you need to pass inspection where they don't 'sniff-test', heh).

 

Dave

[tanderson22]

P0420 indicates that the after-converter O2 sensor is not seeing enough of a difference in reading from the before-converter O2 sensor, that the catalytic converter did not consume as much oxygen as expected, nothing more and nothing less.

 

One of the causes could possibly be a lean/rich mixture problem (other than a small vacuum leak), but you would most likely get a code based on the failure of the computer to obtain the correct mixture.

 

 

Dave

 

I've got a degree in Automotive technology; Thats not how it works..... sorry.

 

The post cat sensor does not monitor oxygen consumption; nothing in the emission system does this. The cat converter consumes nothing.

 

The post cat signal should not fluctuate because the catlytic converter is not creating any fluctuation/ increase in voltage due to a steady, clean emission gas that is stochiometric, clean, or balanced (fully burnt). (Lambda) Steady voltage tells the computer the catalyst is efficent and keeps the monitor out. If it is not doing this, the cat is not being efficient. The exhaust mixture from the engine must switch steadlily from rich to lean (what the upstream o2 controls), which is the minimal requirement of catalyzation, and if this does not occur, the catalyst does not work. Too much O2 and it overheats and the monolith melts down to a slug and when it cools; you stall. Too much CO and HC and you loose the catalytic action if it goes on too long because the platinum and palladium are saturated with these chemicals and have no o2 to combust them to CO2 and H2O with. Sometimes a lot of 02 will revive this type of catalyst. Catalytic converters do not wear out unless they are poluted. Catalyst means it aids in the chemical reaction, but does not take part in. There are no moving parts, and platinum group metals do not wear out.

 

Simply. if the Post-cat sensor sees anything but a steady output, the cat is not efficent and the PO420 or P0430 code will be set, because that is the parameters per OBD specs for the trouble code to occur.

 

IF the voltage fropm the post cat sens were to fluctuate, it would indicate either a rich or lean condition from the converter, which would be "pollution" so the MIL lights up.

 

Differences in reading with the upstream o2 has nothing to do with it;

 

You would not get any codes from any non-emission monitored parts failure, and most P0420 related causes are not monitored.

 

The #1 misunderstanding of CEL diagnostics is to believe it has anything to do with diagnosis or helping a tech out. It has everything to do with Emissions and federal laws passed. It is the evil work of politicians.

 

You are correct in one aspect; it is a mixture probelm.

 

Understanding what the output voltage of that post o2 sensor is; and why that value would occur; is the first step to the solution.

 

From this point you can pay me shop rate for the rest these are trade secrets and the fruits of experience which are seldom shared.

[CNY_Dave]

Where did I say it fluctuates? I never did.

 

And, the 'converter' most certainly does consume oxygen and certain compounds in the exhaust, that's its whole purpose.

 

If you want to be pedantic and say it's not the converter that consumes the oxygen, but that the oxygen is consumed during a reaction inside the converter, that would indeed be more accurate, but needlessly so for this level of conversation.

 

And, the second O2 sensor is most certainly there to measure how much oxygen was consumed in the cat (done by comparing the 2nd sensor's signal with the 1sts).

 

If the actual catalyzation optimization mechanism is to have the mixture altered up and down a bit (utilizing the oxygen storage capability of the catalyst) and the second sensor sees a constant reading, that doesn't change the fact that it's monitoring the O2 level in the exhaust- it's comparing the O2 level against the 1st sensor. 1st sensor, it varies, 2nd sensor, it's constant.

 

 

3-way cat operation:

2NOx → xO2 + N2

2CO + O2 → 2CO2

Oxygen consumed (reacted)

 

CxH2x+2 + [(3x+1)/2]O2 → xCO2 + (x+1)H2O

Again, oxygen consumed.

 

 

Dave

Edited February 13, 2012 by CNY_Dave

[CNY_Dave]

Let me add I'm not trying to be a wongleflute (though I am gifted that way) but you are approaching this from a very specific angle that was taught and may have certain details, and I am coming at this knowing what is going on at the level of what principles are involved.

 

I don't need to be a jet engine mechanic to know that the spinny bits up front compress the air, the air is heated by the compression, fuel is sprayed in,the fuel burns (O2 is consumed), and the hot gasses turn the spinny bits in the back of the engine, and those spinny bits are the ones that spin the front spinny bits.

 

Likewise, I don't need to know exactly how the AF ratio may (or may not) fluctuate in order to make the converter operate optimally to know that the in converter O2 is consumed, and that an O2 sensor can only do one thing- measure the level of O2 (the O2 concentration).

[Ricearu]

I have a degree in automotive technology. I can say that too. Because I DO...

 

The ECM adjusts the AF ratio based on the front O2 sensor. Rear sensor only indicates a problem with the cat or with the O2 sensors. It will not damage the engine by taking it out of the stream.

 

[ivans imports]

here in canada we just smoke one and reset it

[WoodsWagon]

I've got a degree in Automotive technology; Thats not how it works..... sorry.

 

Simply. if the Post-cat sensor sees anything but a steady output, the cat is not efficent and the PO420 or P0430 code will be set, because that is the parameters per OBD specs for the trouble code to occur.

 

IF the voltage fropm the post cat sens were to fluctuate, it would indicate either a rich or lean condition from the converter, which would be "pollution" so the MIL lights up.

 

Differences in reading with the upstream o2 has nothing to do with it;

 

You would not get any codes from any non-emission monitored parts failure, and most P0420 related causes are not monitored.

 

The #1 misunderstanding of CEL diagnostics is to believe it has anything to do with diagnosis or helping a tech out. It has everything to do with Emissions and federal laws passed. It is the evil work of politicians.

Well, I've got an Associates Degree in Honda Automotive Technology, so WOOO hooray for me. I'm also willing to share information and knowledge without coming across as a douche or asking to be paid shop rate.

 

Diagnostic codes have everything to do with helping a tech fix a car. The CEL only comes on if the detected failure could cause the car to emit 50% more pollution than it was designed to, so that is part of federal emissions law. The codes stored, freeze frame data, and live data stream are diagnostic tools though because they give a window into what the computer is seeing and working with.

 

Now, your post cat sensor statement. Earlier cars with simpler programming strategies could be fooled by a resistor pack feeding 0.5v back to the computer from a rear 02 sensor simulator. So for those cars your steady state voltage holds true. Manufacturers got wise to that though, so newer cars look for fluctuation on the rear o2 sensor signal. You will get a P0139 circuit slow response code if there isn't fluctuation on the rear sensor.

 

When a cat has failed to work, the exhaust will pass though without changing its composition, so the rear sensor output will mirror the front sensor output. That sets a P0420 code.

 

By using a o2 sensor spacer to shield it from the direct flow of the exhaust, you cut a balance between setting either code. The sampling rate of the sensor is reduced to the point that it no longer fluctuates like the front sensor, but it still fluctuates enough to not set a slow response code. It works, even on cars with no catalyst.

 

Now, going back to the P0420 code, it can also be set by an inaccurate front 02 sensor. If the front sensor is not following the mixture changes as quickly as it should and is sitting closer to a steady 0.5v, it's signal will look more like the rear 02 sensor. The P0420 is set as a result of the comparison of the two sensor readings, and if both readings are similar, it assumes the catalyst has failed. That is why replacing the 02 sensors can often fix a P0420 code. I've got cars out there that are code free 3 years after replacing just the o2 sensors for a 420 code.

 

Now there's also the bit about o2 sensor fluctuation. o2 sensors are very peaky in their signal variation. Go a little bit leaner than 14.7 and the voltage drops way down from 0.5. Go a little bit richer than 14.7 and it quickly jumps up to 1v. This is the reason that the signal voltage oscillates so wildly with minor mixture changes, and also why the signal output is ignored when the engine has to go rich under higher load. The signal variation does not mean the ECU is feeding the cat lean and rich mixtures to keep it lit.

 

All manufactures have switched to using a/f sensors instead of 02's for the front sensor because an a/f sensor reads accurately over a much broader mixture range, not just 14.7:1 like an o2 sensor.

[Robert Harik]

I've got a degree in Automotive technology; Thats not how it works..... sorry.

 

The post cat sensor does not monitor oxygen consumption; nothing in the emission system does this. The cat converter consumes nothing.

 

The post cat signal should not fluctuate because the catlytic converter is not creating any fluctuation/ increase in voltage due to a steady, clean emission gas that is stochiometric, clean, or balanced (fully burnt). (Lambda) Steady voltage tells the computer the catalyst is efficent and keeps the monitor out. If it is not doing this, the cat is not being efficient. The exhaust mixture from the engine must switch steadlily from rich to lean (what the upstream o2 controls), which is the minimal requirement of catalyzation, and if this does not occur, the catalyst does not work. Too much O2 and it overheats and the monolith melts down to a slug and when it cools; you stall. Too much CO and HC and you loose the catalytic action if it goes on too long because the platinum and palladium are saturated with these chemicals and have no o2 to combust them to CO2 and H2O with. Sometimes a lot of 02 will revive this type of catalyst. Catalytic converters do not wear out unless they are poluted. Catalyst means it aids in the chemical reaction, but does not take part in. There are no moving parts, and platinum group metals do not wear out.

 

Simply. if the Post-cat sensor sees anything but a steady output, the cat is not efficent and the PO420 or P0430 code will be set, because that is the parameters per OBD specs for the trouble code to occur.

 

IF the voltage fropm the post cat sens were to fluctuate, it would indicate either a rich or lean condition from the converter, which would be "pollution" so the MIL lights up.

 

Differences in reading with the upstream o2 has nothing to do with it;

 

You would not get any codes from any non-emission monitored parts failure, and most P0420 related causes are not monitored.

 

The #1 misunderstanding of CEL diagnostics is to believe it has anything to do with diagnosis or helping a tech out. It has everything to do with Emissions and federal laws passed. It is the evil work of politicians.

 

You are correct in one aspect; it is a mixture probelm.

 

Understanding what the output voltage of that post o2 sensor is; and why that value would occur; is the first step to the solution.

 

From this point you can pay me shop rate for the rest these are trade secrets and the fruits of experience which are seldom shared.

 

What a load. He did make one good point: http://forums.nasioc.com/forums/showthread.php?t=2234058

 

http://forums.nasioc.com/forums/showthread.php?t=2156769&highlight=rear+o2+sensor

 

http://forums.nasioc.com/forums/showthread.php?t=1654883&highlight=rear+o2+sensor

 

This code is a problem with all all cars and using the spacer is common, but in california( bay area) they look, and if you have this set up you will fail smog.

 

This is easy to build and works great: http://www.youtube.com/watch?v=YkMD7uS47b4 Only for pre 05?

Edited February 14, 2012 by Robert Harik

[WoodsWagon]

He did make one good point: http://forums.nasioc.com/forums/showthread.php?t=2234058

From that post on nabisco:

Do Not Use a Rear O2 Sensor Extender Bung/Anti-Fouler/etc With a 2005+ Subaru

 

Regardless of what they're called, what they do is to move the O2 sensor physically farther away from the main exhaust flow in hopes of tricking the ECU into not throwing the P0420 DTC when you run headers, a HFC, or a trackpipe. While on some cars they do actually prevent the P0420 DTC from being thrown, they cause fueling problems on all cars 2005 and newer. In 2005, Subaru switched to an ECU that uses the input from the rear O2 sensor to affect fueling in addition to simply monitoring the cat (as in 2004 and older cars). If you remove the rear O2 sensor entirely, or even just move it out of the main exhaust flow, you'll develop strange fueling errors as the ECU tries to make the rear O2 see what it's programmed to achieve. The result of this is slightly worse fuel economy, a worse idle, and generally increased difficulty in getting the car tuned to a good state.

 

Summary: DO NOT USE O2 SENSOR SPACERS OR SPARK PLUG ANTI-FOULERS ON 2005 OR NEWER SUBARUS.

 

 

Also, it's worth noting that you can't use electronic "MIL Eliminators" like the ones from Pony Express on 2005 and newer Subarus either. Your only solution to getting a P0420 DTC on the newer cars is to disable it in the tune.

[brus brother]

Thanks for the link but even more now to worry about with MY05

"Your model year has a problem where it starts to leak very early from the oil return galleries on the bottom of the heads. Make no mistake: it IS a headgasket leak and you DO need to do somehting about it. You'll get no further warning before it converts to a much more serious oil-to-coolant leak."

BOTH of my 05's have the telltale oil leak at the driver's side!

Anybody tracking these leaks and failure rates?

May have to start a new thread.

[unibrook]

Just adding this to a bunch of PO420 threads to help future Searchers:

Just a couple of data points to toss in for those suffering the

occasional PO420 CEL.  My car is a 2001 Forest with 120k miles on

her....yes, she is a Lesbaru.

My CEL PO420 has been coming on

about thrice per year lately.  I plug in my CEL Scanner and erase the

code and drive on my merry way.  Since we do limited, mostly city

driving, it can take a while for Emissions Test Ready reset cycle to

complete.....so you can pass inspection.  This month, it took about 189

miles and nearly 3 weeks of driving to get the pending PO420 to turn off

and the Emissions Ready Green Light to appear in my CEL Code Scanner. 

Then it passed inspection no problem.