Stock exhaust P0420 code. Help!

@GeorgeSanJose switching the o2’s is a great idea.

@Tester @circuitsmith Thanks, ill try that.

@db4690 I respect your opinion and i dont think you’re a jerk. But everyone cheats one way or another. There are so many laws, people just dont always get caught. There are laws that protect people/property and there are laws that drain our wallets. If the OBD2 system wasnt so unfair, i wouldnt have to “cheat”. Who is gonna suffer if i save a few bucks? The state? The shops that make a load of money doing inspections and selling people stuff they dont need? Id like to do it the right way. With a little help i might actually be able to. George had a great idea about swapping the o2 sensors. If the P0420 code changes to bank 2, im gonna return the mils (Hopefully i get a refund) and buy a new o2 sensor. Wish me luck and try not to be so judgmental. Im not a bad person and im not hurting anyone. You could say i might be poluting the air, but certainly no more than a guy driving an old car with no cats. Why is that legal? Nevermind… The system is seriously flawed and unfair… To put it mildly. lol.

@asemaster I got that info from a mechanic… If thats untrue, how unefficiant can a cat be before setting off a check engine light and P0420 code? I dont need anyones sympathy. Not like i can cry on anyones shoulder here lol… Advice is why im here. And i appreciate everyones help. So far i got none from you… If you had something more to offer, id love to hear it. Otherwise save the “Thats illegal” speech for someone who gives a… You know the rest :smiley:

"If the OBD2 system wasnt so unfair . . . "

It’s not unfair

It’s there to inform you . . . the car driver . . . that your emissions system is not working satisfactorily

“The system is seriously flawed and unfair.”

That is your opinion, not a fact

But this is still a free country, and we’re allowed to have our own opinons


I got that info from a mechanic… If thats untrue, how unefficiant can a cat be before setting off a check engine light and P0420 code?

There’s no one rule for that, as every manufacturer may have a different test strategy to determine catalyst efficiency, but generally speaking about 60-70%. Any mechanic who would say 95% to trip a DTC is in the dark about the operation and monitoring of catalyst efficiency.

Who is gonna suffer if i save a few bucks? The state?

Well, I will for one. I have to breathe the same air as you and everyone else around you. Catalysts are there for a reason. Straight-piping a car isn’t really any different than changing your oil and dumping it down the storm drain. How many cigarette butts can I dump on the sidewalk before I’m littering?

True, I haven’t given you any useful advice, because I don’t really have any to give when the goal is to fix your car wrong or not at all.

i can log in, but i cant leave the home page without it showing me as logged out and wont let me reply… PITA! I had to make an account quick to reply to you guys (My hollier than thou BFF’S)

This is Mike btw… You know, the very bad man who might pollute the envirorment with his (possibly) slightly inefficent catalytic converters. *Feels shame :neutral:

@db4690 “its not unfair” Well thats your opinion… And yes, for now we are all entitled to one. lol… They dont just inform you, they force you to comply with ridiculous and hypocritical standards. If they’re gonna bust my nuts, bust the balls of the guy cruising the 1930’s hotrod… And even better, if this is about the environment and not the almighty dollar. The government can pay for propper exhaust systems with our tax dollars. Because as of now, they mostly just create path for a shop to rape someones wallet. Which forces some of us who are on a tight budget to do what we have to. Cant miss work, gotta make that slave wage to feed the kids and the economy. :wink:

@asemaster Ok, 95% might be stretching it… But 60-70% Come on! You gotta show me something to back that up. Im sure you can post a link to something credible.
And read what i wrote to my friend db regarding your environmental concerns. Im with you there, i want a cleaner enviorment too. I think big brother should take some of that money we give them and help us in the right direction. But im pretty sure they are too busy kissing corporate ass, picking our pockets and working us over. LOL.
If your only advice is “Bring it to the shop” What is this place for? Dont get me wrong, i am amused with the legal talk. But i was thinking you’d have more to offer regarding my car. Everyone else was pretty helpful. George actually might save me money and make our enviroment that much cleaner. If its the o2 sensor ill buy one. You judged me and quit on me instantly. It was pretty harsh, but i forgive you. :smiley:

I might not be able to sign into my main account and comment here again. So if i dont return i want ya’ll to know, im gonna do my best at fixing it “the right way”. I appreciate all the great advice. Thanks again :smile:

Mikee, catalytic converters do not usually fail by becoming blocked. Catalytic converters cores are ceramic honeycombs coated with a rhodium-family metal (platinum palladium, the catalyst) that separates the nitrogen from the oxygen when it’s hot and comes in contact with NOx molecules. As exhaust passes through the honeycomb over the years, it slowly coats the catalyst with exhaust byproducts (mainly carbon) preventing the exhaust from contacting it. No contact means no changes to the exhaust composition. Changes to the amount of oxygen in the exhaust are what the upstream and downstream oxygen sensors compare, and when the change is no longer sufficient they ECU trips the code. Checking the converter for flow is good, but good flow does not mean the converter is good.

Yeah, I thank circuitsmith for the description of a MIL eliminator. I’d never heard of that before. But getting rid of a code does not fix the root cause of the problem. It’s analogous to putting electrical tape over the MIL to make the problem go away.

The bottom line is that you’re not going to make the light go away by debating anything about it on the internet. You need to get the cause confirmed and change the part(s).

Regarding the “unfair” question, lots of people do cheat. Lots of people also steal. And commit violent acts against others. The fact that a lot of people do it doesn’t justify it.

The unfair thing I see about the system is that there are so many states without testing. Who was required by the EPA to have testing and who wasn’t was largely a result of highly political, highly biased decisions by the EPA. NH, for example, was required to have an annual testing plan based on the studies when in fact the studies showed that the air pollution was being caused by weather patterns carrying pollution over NH from the industrial states around the Great Lakes.

It is definitely an unfair system. But it helps to realize that these decisions are made by politicians. Scientific studies are used by politicians the same way they use statistics. There is no regulatory agency whose top person was not a political appointee… a politician.

I kept silent but at this point will say this. You continue to blame the car and the car manufacturer by stating that “it’s not fair” and now pile on with the “government can pay for a proper exhaust system” and “mostly create a path for a shop to rape someones wallet”. That’s all total BS.
Modern exhaust systems are excellent.

Exhaust systems hold up very well and if you have a converter problem then it’s likely due for the same reason you’re struggling with now; trying to cheap out. A converter can fail due to a number of reasons including lack of maintenance. I’m assuming from the tone of this post that regular maintenance is not high on your agenda.

As to those MIL eliminators they’ve been around a while and the EPA is investigating them. The manufacturers and vendors give themselves an out by claiming they’re for “offroad use only”.
Translated: The buyer chose to use it on a public roadway; not our fault as we had no idea.
It may get to the point where a vehicle with an illegal item such as this may just get impounded.

As to the 1930s hot rodders you’re also offbase on that. Not only are there comparative few of them on the road and not driven daily the owners do one thing that you do not . They take care of them religiously by keeping them in an excellent state of tune.

In Georgia they check for the cats being removed using a mirror and fail the vehicle if they have. I’m sure their are some stations that would pass it, but I know the one I use wouldn’t.

I think I’m a credible source. Not trying to be snarky or have a big ego, but I’m a mechanic with over 25 years experience, an ASE Master Technician, state licensed emissions specialist, and train other mechanics for the state emissions program.

There’s not going to be a link to anything because catalyst efficiency is far more complicated than a link showing percentage efficiency or watching O2 sensors. Your mechanic who thinks that it’s that simple doesn’t understand it either. In a nutshell,

Your check engine light will come on and the car will store a fault code when the car detects a failure that will cause the tailpipe emissions to rise to 150% of the emissions standards outlined in the Federal Test Procedure. In the case of the catalyst, the car has to run the monitor and fail it twice before a fault code is set. Obviously the size and design of the engine, the size and design of the catalyst, single or dual exhaust, engine condition, driver operation, and detection strategy would all play a part in a catalyst fault.

Is it possible for a catalyst to only be operating at 75% and still have tailpipe emission below 1.5 time the legal maximum? Sure it is. Is it possible for a catalyst to be 95% efficient and still fail a catalyst monitor? Sure it is.

Since you’re not able or willing to have the car properly diagnosed, my advice for keeping the light off is check for exhaust leaks and repair as needed, replace the rear O2 sensors, replace the cats.

Alternately, take all the aftermarket stuff off the car, and find out if your state has a waiver or Consumer Assistance Program to help aging cars or gross polluter cars pass emissions.

+1 to ase’s post.
I’m afraid you’re just gonna have to fix it. The state waivers that I’m familiar with require you to spend a minimum (substantial) amount and prove that you’ve attempted to fix the problem but cannot. These waivers are designed specifically to prevent an owner from using the waiver instead of fixing the vehicle.

I remember as a child in the mid to late '60’s visiting California and some days the bad air made my eyes and throat sting; the sky looked tan instead of blue.
In 2008 I visited China and it was worse. On a “clear” day I could look directly at the sun.
Air pollution is a serious problem and every little bit hurts.

I lived in the L.A. area for a short time in the early 70s and you’re right about the sky. The mountains were just a faint outline in the brown haze.

Re the “unfair” comment. If you’ve followed my High HC problem on my Corolla, you know I’ve posted before about aspects of emissions testing here in Calif being less than optimum – that is if the goal is to reduce air pollution but still give the diy’er owners the best information and opportunity possible to comply.

I wouldn’t agree with the OP that it is the OBD II system that is unfair. What’s unfair – I’d phrase it as “not optimum” – is the difficulty a diy’er has with finding out what’s causing the problem. I think if the OP (Mike) knew for certain one of his cats was no good, and that replacing it would make the car pass emissions easily, he’d simply pay up for a new cat and replace it. Likewise if it was one of the O2 sensors.

The problem is there’s no method to test either the cats or the O2 sensors that is available to the diy’er. And replacing them one by one, retesting emissions, trying again, and hoping for the best is unrealistic and much too expensive. For example, most parts shops won’t allow you to return cats and O2 sensors unless they are unused and in the original packaging.

So diy’er OP Mike is put in an untenable situation. Especially when under the time limits and fines if exceeding those time limits imposed by the DMV.

So what’s the solution?

For one, the DMV’s emissions department could offer a big hand up to the OP. They could publish the emissions data they’ve gathered for similar cars with similar engines, and which fixes worked in which situations. And they could offer telephone assistance from emissions trained mechanics. And as long as the owner was clearing trying to comply, the registration would continue to be renewed, perhaps 3 or 6 months at a time.

Probably most folks here will agree in part at least with what I’ve said to now. This last part may be more controversial. If the owner did everything the DMV mechanic said to do, the car remained in unmodified condition with all OEM compatible emissions related parts, and it still didn’t comply, then the emissions problem should be given to the manufacturer of the car. Why? Because the problem is almost certainly a design or parts defect. A dealership shop should then take on the job at their expense and do what is necessary to make the car comply. The reason I like this idea is b/c it gives the manufacturers an incentive to design and build cars what are easy to diagnose if there’s an emissions problem.

A dealer could certainly take on problems like this at their expense. There’s going to be an argument against that though.

This means the MSRP of the car when new is going to take huge jump up for the person buying it; guaranteed. The customer who buys a new car now is paying as part of the MSRP a budgeted amount for warranty repairs already; they just don’t know it. Covering someone for an eternity is going to add a bunch more to that window sticker.

What if that was listed separately on the window sticker? Think the customer would get irate over a new car having an “Emissions Repair” figure listed as 5 grand extra or would it be buried in the MSRP price same as the warranty repair figure to keep the turmoil down…

The shop labor rates are going to go up on all repairs not even related to emissions faults. There is no free lunch. That 100 dollars a flat rate hour would become 125 or more and parts pricing would also rise along with fees and taxes.

This car is 16 years old and just because an O2 sensor and/or converter has allegedly failed at 90ish thousand miles does not mean there is or was a design flaw.

I honestly don’t see what the big controversy is

you’ve got a man who knows his car won’t legitimately pass the smog inspection

He’s nowhere near the point where a referee would get involved

he hasn’t even performed any repairs yet

“mil eliminators” are not a repair . . . they are tampering

he thinks “the system” is rigged, and not in his favor

He doesn’t want to pay a shop to diagnose and repair the car. It seems to me he thinks he shouldn’t even have to

That’s life . . . nobody is qualified to do everything. At some point in our lives, we have to admit that we can’t do something, and we pay somebody else to handle it. I’m comfortable admitting that fact. There’s lots of things I can’t do, and I know it.

OP, if you’re reading this, I don’t have any grudge against you

We just disagree on certain things

I also agree that there is nothing fundamentally wrong or flawed with OP’s car

it needs to be fixed, and that’s all there is to it, really


I had a military layover outside of LA in '71 and explored the area with a couple of fellow GIs. The air over LA was thick enough to butter on bread. There’s no question in my mind that the Clean Air and Water Act was necessary and the EPA has done a great deal of good. However, I personally believe that they’ve run amok, as regulatory agencies tend to do.

But that’s a whole 'nother discussion. In this case the OP simply bought a fast looking hot rod that he knew had a Check Engine Light illuminated. And now he’s trying to find a cheap way around fixing it because he apparently spent all his money on the purchase and can’t afford to fix it properly. I sympathize, but the only suggestion I can make is to either find a way to get the money or get a bus ticket and consider this an expensive lesson on looking past the purchase price… and on never buying a car with a CEL illuminated unless you have to cash to fix it. This one is in no way the EPA’s fault, the seller’s fault, or anybody else’s. It was just a bad decision, probably caused by being blinded by the car’s hot looks.

I agree with mountainbike about the EPA and other government agencies. They’re necessary but sometimes go overboard with things.

There was a news article a year or so ago about some government regulations pertaining to the auto business and while I can’t remember all of them there were a few that stuck with me.

One is a dealer being told his roof is draining water off the showroom roof too quickly and violating water runoff rules. Slowing water runoff may lead to leaks or a roof collapse.

Another is that the hood of a car must clear the engine by at least 3 inches as part of the crumple zone factor. This means raising the seats which means raising the roofline which means changing the wheels to keep it in proportion.

Homeland Security regulations state that a potential terrorist is not supposed to get a car loan. I wasn’t aware there was a YES or NO box to check on a line which asks “Are you going to use this vehicle as an IED?”.

The head of NADA stated that 21% of the cost of a car is related to conforming to regulations and the only surprise to me is that the number isn’t higher than that.

“One is a dealer being told his roof is draining water off the showroom roof too quickly and violating water runoff rules”

That one is simply hysterical. Thanks for the laugh.

The problem is there’s no method to test either the cats or the O2 sensors that is available to the diy’er.

There is no special license required to purchase a scan tool and learn to diagnose your own car. If someone wants to own and repair older vehicles they need to buy tools, no different than the need for an oil filter wrench to perform your oil changes.

A scan tool that displays live data can be found for less than $100, seems affordable. This is not an economical vehicle to operate, it couldn’t have chosen to meet a tight budget.

Autozone has the Actron CP9575 for $90. I have never used one, they claim it displays “live real time data”.

The problem is there’s no method to test either the cats or the O2 sensors that is available to the diy’er.

I’ve said this before here. With the exception of certain security-related components on European cars, anything and everything anyone needs to service and repair their own cars is available to anyone anywhere. All the tools, equipment, service information and technical bulletins needed are available to anyone who wants to buy them. If you’re interested in fixing your own car, there’s nothing stopping you from buying the tools and learning the technical info and going about it yourself. There are even web pages like with people there willing to help you.

For one, the DMV’s emissions department could offer a big hand up to the OP. They could publish the emissions data they’ve gathered for similar cars with similar engines, and which fixes worked in which situations

There are already programs like that out there, with the bulk of the info gathered from professional technicians who have figured out pattern failures, work-arounds, unique testing procedures, and alternate methods of achieving a proper repair that may not be outlined in factory manuals. But you gotta pay to play. We don’t work and give out our results for free.

And as long as the owner was clearing trying to comply, the registration would continue to be renewed, perhaps 3 or 6 months at a time.

Doesn’t the renewal notice come a month ahead of time? How much time is needed to get a car through smog? The only legitimate reason I can think of is a car needing a dealer-only part that’s on back-order. More exceptions and extensions just mean more avenues for people to circumvent the system.