I have changed my mind. I'll argue some more.

About cars, it's clear I have more experience and skill than you have when it comes to working on them. About language, it's clear I have more skill at getting my ideas across, I am more articulate and I can better answer direct questions.

But when it comes to just talking nonsense, you surpass me. There is no argument there. Your use of language is somewhat stilted. You make the wildest assertions and assumptions. You put words in people's mouths. Your failure or refusal to answer direct, civil questions makes you impossible to work with. I don't know why you do that, but it's not really important. You either don't know, or you do know, but you don't say. Your bluster and evasion, while entertaining, is unhelpful at solving the question at hand. You post bullshit, get called on the bullshit, and ignore it. I would too, had I posted the crap you posted.

I'll give you another chance. What you do with it will be interesting. Will you demonstrate your knowledge and civility and answer the question? Or will you dodge it again, demonstrating your ignorance and hostility? Either way, I'm looking forward to your next post.

tw: Will you please explain how measuring gas mileage will fix a rough idle, as you asserted in post #92?

TW, what outstanding questions? You mentioned hooking it up to a computer and revving it. I don't have the tools to do that. Was there something else?

I drove it a short distance this morning, and it never had a chance to warm up. The idle was fine. But since it's only a problem when it's warmed up, it behaved as expected.

I think the problem is caused by the flint on one of the spark plugs needing replacing.

No, no, no...the flint stones didn't use fuel or spark plugs or oil drums. They just ran along with their feet hanging out of the hole in the bottom of the car.

Many examples were requested. Other patterns may exist but would only be apparent to you.
Number must be provided. That was only what you feel. How many gallons (to at least a tenth of a gallon) per how many miles? And what were those MPG numbers back in better days?
So what does it do when at 800 RPM? 1200 RPM?. When cold. When half warm. When hot at all those RPMs? Cold unfortunately means 800 RPM symptoms are not possible. Apparently it is still doing it hot. But at what temperature on the gauge does it start getting rough? Or does it only get rough when the high idle finally drops to 800 RPM.

Not yet stated is if you even have a tachometer on the dash - an example of information I was waiting for or had to assume was not relevant.

What other techniques were used or tried unsuccessfully to aggravate and diminish roughness? What parameter change when it becomes better or worse?

Previously discussed were the two separate systems. Idle and normal operation. How do symptoms change or exist in both modes?
The dealer connects an onboard computer. Or buy one for something like $150. However you must then learn the technology - which a dealer provides with his better computer for a fee. That onboard computer is how dealers find intermittents - should you need it fixed now. It is an option reserved for the future. But the option is how these type problems can be located.

Have you been flooring it after each restart as requested?
More suggestions. While idling, put your ear near the exhaust. Listen. Does it run smooth? Is there a pattern or sound? How does this also change with the next tank of Shell? How does it change with cold and warm? Examples of details that might quickly identify a problem without hiring an expensive dealer mechanic.

So what else was changed in the few thousand miles before this happened. Change of gas. Change of spark plugs. Anything else. All are example of what was noted early: I am assuming this problem still exists. Because nothing said so definitively. Is it still as bad? Or has it diminished as implied in a later post or with another tank of Shell?

If the idle is rough, just sand it down until it's smooth.

Hey! I'm trying not to be abrasive here.

Fuck. Check engine light is on. Got the codes read at AutoZone, they say:

P0421 - Warm up catalyst system (RH) efficiency below threshold
P0431 - Warm up catalyst system (LH) efficiency below threshold
P0174 - Lean Air/Fuel ratio bank 2

I know it will not pass inspection with this issue. But I just passed in November, so I'm safe there for 11 more months. My question is, is this a dangerous thing to be driving around with, or can it hang out for a few months with no real problems other than continuing to degrade a catalytic converter that is probably going to need replacement either way? I have to drive this thing for about 10 hours of holiday travel in just a couple weeks, and fixing it right now is going to be very painful.

I'm replying based on experience, not on knowledge.

Before panic, try filling the tank with "good" gas... not higher octane, but from a trusted gas station.
Be sure the cap in on tightly, as it should be
Try driving thru this first and maybe second tank of gas to see if the light goes out, and or the codes disappear.

This experience did happen with my grandson's Subaru, and the new gas did the job.

Best of luck...

You're fine.

This thread is instructive I believe (I'm guessing about your rig, other symptoms, etc). But the description seems on target. Short description: your catalytic converters are failing, gradually. This is determined by examining the exhaust flow downstream of the converters, and comparing it to some threshold. Yours seems to have crossed some threshold. It should drive fine.

and by fixing it being painful, you mean that you don't have $2000 for two new converters in your wallet, yeah?

Yeah.

This was what I was initially hoping. However, I have one of those cars where the light does not go off by itself, it must be manually turned off once triggered. And since this has to do with emissions, no shop that does state inspections is allowed to shut it off without a thorough investigation of the problem. One guy did turn it off for me on the sly, and it came back on again a couple days later, right after another refill of the gas tank. I don't think he'd do it again.

Anyone know how to turn off a check engine light?

year make and model?

black electrical tape.

2003 Mazda MPV

Grr. Someone clipped the front driver's side corner of our car today. It was parked on the street near the elementary school and they were pulling in front of it to park. It looks like we'll need a small dent hammered out of the fender, a new light housing, and a new front bumper.

Fortuneately, they left a note on the windshield. It's even someone we know.

And the really good news is that we need to get it inspected this month, and Mrs. Glatt had just inspected it a couple hours earlier. So there won't be a rush to get it fixed AND inspected before the end of the month.

Fuckin Christ

Yeah, assuming that it really truly is a failing emissions level triggering the light, and not a poor gas mixture like Lamplighter suggested. If it's a gas mixture problem, turning off the light may allow it to stay off, or it may come back on again and then I'll know for sure.

Mr. Clod and I were calculating, how many "expired inspection" tickets I would have to be pulled over for before it became worth the cost of a new catalytic converter... it's a lot of tickets.

Just pulling stuff out of my ear here but ...
The fact that both LH and RH (left hand and right hand?) catalysts are showing errors at the same time suggests either:
a. These catalysts are shitty and have a poor lifespan built in or
b. The catalysts are fine and the problem is caused by some factor shared between them, most likely the gas you are using.

B. Let it be b.

ETA: or c. the catalysts were fine but have been irreversibly cocked up by using shitty gas. Hope not.

You've got the cats, and some sensors (usually oxygen sensors) to report back to the computers how the cats are performing. A bad report could be a failure of either.

Only after you're sure of what the problem actually is, then explore your options
Here's a couple out of a list of 76.

The combination of codes imply a least expensive suspect. To say more requires information you cannot obtain.

Appreciate what you have and what is relevant. Oxygen sensors do nothing until the engine heats them to maybe 600 degrees. During a warm up period, the engine dumps larger amounts of gasoline into the engine. Much unburned gas is then burned by the catalytic converter when it gets hot.

Once the oxygen sensors get warm, then the engine computer changes a fuel input. Leans out the mixture based, in part, on data from an oxygen sensor.

Apparently you have two sensors. If one is proving bad data, then the engine will dump improper amounts of fuel into the engine. This can result either in a too lean mixture (causing exhaust valve failure) or too rich (causing catalytic converter failure).

A most likely suspect is a bad oxygen sensor. Fix it now to avert damage that may cost $thousands.

Bad gasoline causing this problem would be noted by mileage changes approaching maybe ten percent. Of the maybe 100 other possible errors associate with the converter, gasoline might only explain less than ten.

This failure could be something as simple as an oxygen sensor with a failed heater. Then the engine computer, after a delay, would be expecting data that was incorrect. Or it could be a thermal junction failure inside that sensor. Either way, a $100+ sensor is a least expensive solution. I believe you have two. Don't know if the shop will want to replace both or just one.

Again, your reply is only as useful as facts first provided. You (typically) cannot obtain numbers necessary for a better answer. The shop can.

But in that case, wouldn't the presence of both (LH) and (RH) codes mean that both oxygen sensors had to fail at almost exactly the same time?

Your cats are covered by a 8 yr /128,000 km waranty, has that expired?

Yeah, it was eight years old this past January, and has almost twice that mileage. But I've decided I can afford the diagnostic, and if they tell me I need new catalytic converters, I'll just tell them no and start figuring out how to wreck the thing for an insurance payout. ;)

i talked with a friend of mine about this. we came to the same conclusion. if the "good" gas doesn't solve your problem, replace both of the o2 sensors at the cat first. then if you still get the codes, you have a bad cat.

BAAAAD KITTY !!!!

Might be something here http://www.ifixit.com/Browse/Vehicle

If you need new converters, then an engine defect caused premature converter failure.

I mentioned two oxygen sensors. One before the converter and one after. Many cars do not use a sensor after the converter. But all must have the sensor before. Why would an engine problem cause its computer to detect those errors? A first sensor is giving bad numbers. Engine responds with a bad fuel to air ratio. Then a sensor after the converter reads bad numbers.

You don't know what to replace. This is just one likely suggestion. A likely suspect is one oxygen sensor causing bad numbers or improper engine operation. I see no reason to jump to a bad catalytic converter conclusion. Follow the evidence before fixing anything. The above scenario describes one possible reason for those codes.

Is the evidence a trail of money? Because I could follow that, and then fix anything.

In string theory, we believe reality has 11 dimensions (not to be confused with the twelve taught in AA meetings). Money is a low level domain where the most corrupt cut throats to collect cash. Higher level diagnostics and equipment reside in a dimension where Dollars never appear in diagnostic error codes.

Raise yourself from a dimension dominated by business school graduates and other primitive species. All praise the gods of math and science. All chant verses of logic.

Several forums mention this as one of that model's weak points... a common occurrence.

Are we talking about a car here? Cause if we are, you have just blown my teensy brain for the day. I should have had another cup of coffee before I read that. DAMN YOU TW!!!!! :p:

this is a good plan.

Wellll... looks like it might have to be my plan after all.

It definitely is the catalytic converters failing. Both failed at the exact same time? Yes, because apparently what happened is the one failed, and then the added strain on the other was too much for it to bear so it failed very shortly after.

So! I have new questions to be answered by knowledgeable people who aren't automatically inclined to get me to pay them.

1.) He says that while replacing both catalytic converters would be about $2000 all told, he can replace them with "universal" (i.e., off-brand) parts for a total of about $600. BUT, there is no guarantee it will work for any set period of time, or even at all. He hinted that this would really only be the option to pursue if we wanted it to work just long enough to sell it. But there is a chance that they could put them on, they would be completely nonfunctional with our vehicle, and we would be back where we started but $600 poorer. What are the chances these "universal parts" will indeed work with a 2003 Mazda MPV, for whatever length of time?

2.) He says that while we can continue to drive with it the way it is for some length of time, it won't be a steady decline into failure. The exhaust will get thicker, and the mileage will get worse, but then at some point in the possibly near future the house of cards will fall apart and I will suddenly only be able to go about 10-15 miles per hour. This doesn't sound to me to be the way a failing engine would work, but I know jack shit about it. Is this correct? Because I can deal with gradual, I can't deal with the engine giving out on me in the boonies halfway between here and Houston.

I had a friend years ago who had a similar problem. This was in a state with no emission testing at the time. Her cat also failed to the point that the engine wouldn't run properly. The cat was basically plugged and wouldn't let the exhaust through. So a mechanic told her he could poke holes with a screw driver through the guts of the converter to allow the exhausts a pathway through. This was illegal and allowed the exhausts to completely pass through the converter without being treated. Bad for the environment, but she got a few more years out of that car.

I doubt you could find a mechanic willing to do that for you, and it would only buy you enough time to make it to your next emissions test, where they might prosecute you when they see what you've done, but it's probably not all that hard to do yourself. Understand that I'm not recommending this, just relaying a story.

hm.

I'll tell you what I know about catalytic converters, Clodfobble. See if there's something there for you...

The catalytic converter is aptly named, it uses a catalyst, notably platinum, to convert substances in the exhaust stream to less toxic substances. The platinum, and other magical chemical stuffs, aren't consumed by this process, just used like eeensy weeensy chemical tools to rearrange the compounds flowing past. Mechanically, a catalytic converter works like this: take a double handful of drink stirrers, the hollow kind, and wrap your fingers and thumbs around a large bundle. Now, pick up the bundle and look through it. Weird, huh? It's like a straw of ten thousand tubes. Your catalytic converter is like this, but with tinier holes, and lots more of them. The surface of the straws are coated with this catalytic compound. The whole thing looks like a brick, except along the axis of the "straws", through which the exhaust flows. This "brick-thing" is contained in a kind of can with the exhaust pipe running in one end, through the cat, and out the other end.

When the exhaust gasses heat up the cat to the normal running temp, the chemistry does its magic, making the exhaust less toxic. That's when things are running right. But, naturally, things can go wrong. There are a couple MAIN ways a catalytic converter can fail.

It can be ruined chemically. One easy (well, used to be easy, now it's harder, but you get the idea) way is to run a tank of leaded fuel through the car. The car will probably be ok, but it will poison the catalytic converter. It's a goner. The lead ruins the surface so the chemistry doesn't happen. The car will run fine, but the emissions will be bad. There are other ways to degrade the cat too, if your car is burning a lot of oil, that can crap it up too. So, you can foul up the cat chemically (pun intended).

You can also ruin a catalytic converter mechanically. That "bundle of straws" I was telling you about? In the cat, they're made of ceramic, like your.. well, I don't know what it's like. but the upshot is the thing is FRAGILE. And it is impervious to heat, that is, you can't melt it, and "send it down the tailpipe". If it gets broken anywhere, even a little, it will crumble, maybe slowly, maybe all at once, and you will have a MECHANICAL obstruction to your exhaust flow. This, as you may well imagine, is bad. This is (probably) the "plugged up" scenario you heard. I can hear a failing catalytic converter, they have a distinctive tinkling sound at low speeds. That is from the ceramic element rattling around in the metal box that contains it. When they're new, they are neatly, and tightly fitted inside the box (it could be many different shapes, box, cylinder, tube, lozenge, etc, whatever). As the car is driven, and it gets shaken around, it's possilble that this ceramic honeycomb gets rattled around and maybe knocked loose a little. Imagine it's still in there, but knocked around some, so that the corners are rounded a little. Now it just sits in the can, which is fine, but it's a ceramic "brick" sitting in a sheet metal "can" attached to the exhaust plumbing. It's gonna rattle. That's what I can hear, you could hear it too.

Anyhow, the cat that comes with the car is designed specifically for that car in lots of ways. Like, where it connects, how hot it will get when the engine is running normally, how much flow it can accomodate, how much catalyzing surface area is available to the exhaust, etc etc etc. Your "universal" one isn't designed with these specific parameters in mind. It likely has the same chemistry setup, but will it be hot enough? too hot? too restrictive? too "loose"? etc etc etc. These are the kinds of unknowns that give the mechanic pause regarding the efficacy of the universal parts. I think the chance that the universal units would NOT WORK AT ALL is low. Unless they're like, mock ups or some other nonsense. I think you could just BYPASS the flippin converters all together and the car would still run, but you'd be passing untreated emissions. But the car would run.

Does this help?

V: Once that catalyst is destroyed, doesn't the exhaust develop a really stinky smell.

I've been behind cars that had such a stinky exhaust,
and I humored myself by thinking it was a bad converter.

Could be. ??

Stink is often sulfur, and I associate sulfur with diesel, not gasoline, but certainly, if you're not treating the exhaust as designed, there could be such a side effect.

That type of failure means one converter failed months earlier. And the oxygen sensor only for the failed converter was reporting that failure long before a second converter failed. You did not report those those symptoms.

To have both converters fail so quickly requires something that causes complete damage in maybe one day. For example, contaminated fuel that permanently damaged both converters.

A catalytic converter simply burns gasoline that an engine did not. Converts unburned gasoline (and other pollutants) into nitrogen, oxygen, water, and other non-pollutants. A failed converter does not reduce gas mileage. It just stops converting gasoline, et al to non-pollutants.

Only way a converter can reduce mileage is to collapse and restrict exhaust flow. This becomes obvious from a noticeable reduction in acceleration and decidedly changed engine noise. Two converters do not fail within the same hour. I would get a second opinion.

What will a mechanic do when changing a converter? Automatically replace oxygen sensors that might be defective. Then the vehicle owner can only assume the mechanic was correct.

A P0174 error code is unrelated to the converter. Implies an engine problem; not a converter failure.

The vehicle is a six cylinder engine. Usually, two converters mean one for three cylinders with no connection common to all six cylinders. If all cylinders connect to a common pipe, then much less expensive is to design one converter for all six cylinders. All six cylinders connected to both converters leaves me suspicious. A third reason why I have trouble with his conclusions.

What happens when one oxygen sensor fails? It reports a too lean mixture. So the engine dumps too much gas into cylinders and converters. While dumping maximum gasoline into the engine, a failed oxygen sensor still reports “too lean” - error code P0174. A resulting overheated converter fails due to burning too much unburned gasoline. I don’t believe this is your problem. But it is another example of what better describes your symptoms.

Big V - excellent description.

Lamplighter - stinky exhaust can also be a car running on LPG or even biodiesel.

TW - yeah, that bit about one cat failing thereby "putting extra strain on the other"... :eyebrow: assuming they're parallel, this makes no sense.

But could they be serial?

Come to think of it, probably not, because it doesn't explain the LH and RH codes. Ideas, anybody?

Which symptoms was I supposed to report? My check engine light was not on prior to this episode. It was running fine; still is.

In fact, the check engine light has not yet come back on, since it got shut off yesterday after the diagnostic. I'mma keep waiting...

Think horses, not zebras.

If your mechanic reset the check engine light and you are driving with "good" gas,
I'll suggest that both converters did NOT fail at the same time, or at all.
Instead it was a loose gas cap or something like that.

If the check engine light comes back on right within just a few miles, that's one thing,
but if it stays off for a longer, I suggest it's your mechanic that is failing.

Get a second opinion, or third, from a reputable establishment.
.

Yeah, when the other guy shut it off for me on the sly, it came back on within 2 days I think. So we'll see. I'm certainly not having any work done on it if the light stays off.

I also went ahead and ponied up for a guy at justanswer(.com.) Basic freelance expert site, about $18 for a conversation as long as you need it to be, I've had success using them before. Anyway, he said yes, the catalytic converters in a Mazda MPV are in parallel, but if one is mostly plugged up, then it will cause exhaust to back up into the engine and thus be forced by pressure into the other one, leading to the "added strain" effect. He said it was kind of unlikely, since the parts are the same age, it's not like I have one terrible one and one that's fine, unless maybe one sustained damage at some point (which is possible, I did go over a really violent pothole over the summer that knocked my alignment way out of whack.)

He noted, however, that there are also two O2 sensors, and one wouldn't affect the other, so even if it is actually sensor issue we're still looking at two sensors going bad at the same time (which is pretty much the issue tw noted, except instead he accused me of not mentioning that the first O2 sensor must have been failing months ago. :)) He said the only other possible thing that might cause these codes is an exhaust leak somewhere up the line that might be confusing both O2 sensors, though he said again this would generally cause a sensor code, not a converter code.

If a first failed converter put extra strain on the second, then you reported a failure of the first converter a month plus ago. A second converter failed only recently. As I said, those are the symptoms you were supposed to report if the mechanics diagnosis was accurate. You did not report those symptoms.

You did report symptoms that, for example, report a failing oxygen sensor. It was probably first failing as much as a year ago. Could have been seen long ago by a computer attached to the diagnostic ports. But only recently got bad enough to cause an error code. Do not confuse that oxygen sensor with others on the converters - which, in hindsight, I believe you and others were doing.

Meanwhile, the mechanic's analysis (bad converters) do not explain error code P0174.

An intermittent error code implies your always existing failure is slowly getting worse. Or only gets reported when detected in consecutive engine restarts.

Furthermore, error code P0174 may not cause a check engine light. May be detected repeatedly by the engine computer. But only reported on its diagnostic port.

Some designs have a ‘diagnostic plug’ that, when attached, causes unreported error codes to appear as a flashing check engine light.

Driving conditions (and even different gas) may cause a marginal problem to be worse. Always there and detected by monitoring numbers from various sensors. Those codes can be created by a long list of possible suspects. Blaming two failed converters was way down the suspect list.

Suspect list could be shortened significantly by monitoring numbers from various sensors, as noted above. But you cannot do that without a maybe $120 computer that plugs into every car's computer (ie Car Chip). Check engine light can be cleared by that layman’s tool, or sometimes by a ‘diagnostic plug’.

A least expensive solution is to watch this problem. Wait for it to become so obvious that any mechanic can fix it the first time. However if a check engine lights repeatedly, then fix it now to avoid possible future engine damage.

I suspect a P0174 error code still exists. That error code, alone, does not trigger a check engine light. But my wild speculation is based only in experience - not in facts required from the shop manual. Speculation is best anyone here can do without further information from that plug-in computer (sold even in Sears and Wal-Mart) and from a shop manual.

Your best suggestion is in a paragraph that starts, "A least expensive solution ...". I, on the other hand, have a nasty habit of doing things on cars that also exposed Saddam's WMDs and Tokyo Electric's lies about Fukushima. Ruthlessly, finding numbers and irrefutable facts (that explains all three error codes) requires information currently not available.

Or even as cheap as $76.00. Looks like a neat little device, actually. Perhaps...

this

Sorry, Fob. If it were me, I'd go for cheap fix and trade in, but I'm kind of biased because that's the point I'm at with my van. Or at least was before I wrote off the Focus....

Instinctively I would have, but the guy scared me with the possibility (or outright lie?) that it might be completely non-functional with my car, and we'd be $600 poorer and no better off.

However, the check engine light has not yet come back on. We shall see, oh, we shall see....

Well this has turned into a complete clusterfuck.

We told the mechanic we did not have the money for the repairs, and at any rate, we didn't have the time or energy to deal with this until after the holidays. He says no problem, but hey, they've got a no-interest financing option, and we should go ahead and apply for the card today so that the account will be active when we're ready. We are resigned to having to fix this at some point in the future, so we do the application. He also says that since the parts will take awhile to come in, he will order them now so that they will be in stock when we are ready.

So we drove all over Texas during the holidays, probably 1000 miles total, and the check engine light still did not come back on. The mechanic called me several times just before we left, and just after getting back, pushing me very hard to come back in and have the repairs done. Suspicious, we took it to a second mechanic... and the emissions tested just fine. Catalytic converters are A-OK, they said. HMMM.

We are prepared to call this a simple error on the first mechanic's part, though we suspect he may have known that the initial error was really just a bad tank of gas. But before we can call him to tell him the "good" news, he calls us and leaves a message cheerfully saying that they have gone ahead and charged the no-interest account we opened for $2,303, for the repair we "authorized," and wondering again when we will come in and have it done.

What the fucking fuck?!

Mr. Clod calls, and lets the guy know 1.) about the good test results on the catalytic converters, for which the guy has no explanation, 2.) that we have closed the goddamn account, and 3.) that we will be disputing the charges, and he's insane if the thinks that the card issuer is going to let him charge for parts he still has in his possession and labor he never did. The guy starts talking about restocking fees for the parts, and the conversation ends at an impasse, with Mr. Clod refusing the proposed 25% and the mechanic saying he'll check with the parts manufacturer and find out if they can "cut us a break." We actually agreed between ourselves that we'd be willing to pay 10% (of the parts cost only, certainly not the labor) just to make the problem go away, but the guy never called back to negotiate further.

So fine. Royal screwing averted, never going back to that mechanic again. Still have to deal with getting the charges off the account, but we feel confident that will happen, it will just take some legwork. Done and done.

And then yesterday, the check engine light comes back on. Fucking fuck.

If the shitty mechanic had just been patient, we'd be in his shop right now, getting the repair done. But his behavior regarding the credit card is unforgiveable, so at best we're going to someone else. Except, of course, we still don't have the money for the repair, and what are the chances that we will be able to open a no-interest car repair account now, when we just opened one, closed it days later, and currently still have $2300 sitting on it? I find that unlikely.

Kelly Blue Book is worse than we thought, the minivan is at best worth $2300 in its entirety, maybe less. So I purchased an OBD-II code reader off Amazon, with which I can shut off the light myself, and hopefully we can trade it in quickly before it comes on again. We did find another MPV at a dealer that is 2 years newer, has less than half the mileage, and is listed at $8000. So that's probably the one we'll get, if we can make the trade-in work.

Sigh.

Geeeeessh, what an episode.
If you've not signed a work order, just deny deny deny.

Maybe once you get the check engine light turned off, and good gas,
it might help to invest in a new gas cap, and be sure it's on tight at each filling.

A second mechanic on a different side of town might be a good investment too.

It's not the gas cap, man. The code that came up today is the same one as before, failing catalytic converter. The car is almost 9 years old and has 155,000 miles, it's not that surprising.

Clodfobble - what you suggest seems a bit unethical.

Now that you have a reader, view the oxygen sensor voltage yourself. As posted long ago, if the O2 sensor is defective, it is reporting a voltage reading that is off on the edge. Intermittent. Therefore the engine computer is intermittently dumping wrong amounts of fuel into the engine. Different gas even from the same station will push that marginal voltage over and back behind a failure line. Obvious when the diagnostic port provides an actual volt number.

Still never answered were answers to tests that would have said so much more. For example, floor it after each restart. Because (and again) some defects are only reported when the accelerator is moved the exact same way after every consecutive restart.

Eventually that defect will become so bad that any mechanic can find it. But this you know because my post was based in provided and known facts. No reasons existed to suspect catalytic converters as defective. Your emission tester only confirmed what was obvious because reasons for that conclusion were also posted.

Engine light and code does not say what is wrong (as others have mistakenly assumed). It only says where to start looking. “Looking”: as in CSI's, "Follow the evidence." Viewing actual numbers - ie voltage from that oxygen sensor. Which is read from the computer by an OBD2 reader (ie Car Chip) attached to the diagnostic port.

What should be obvious to all and is obvious to you - a gas cap has zero relationship to what comes out the exhaust.

Now, did the $2+K mechanic explain the whys as I have done? Welcome to everything in the world. Without reasons why AND numbers, then the guy (any guy) is probably lying. Welcome to history taught by Saddam's WMDs.

Better dealers have a big computer that both reads those numbers AND does the voltage analysis for them (and you). Did the garage that did emission tests use that computer? Or just test emissions with a wand inside the exhaust pipe? Did he provide actual numbers for CO, CO2, NOx etc? Nobody cares if those numbers are good or bad. Only relevant is the actual value and what the manufacturer limits for each were supposed to be.

Whereas the problem could be with other system parts, one likely suspect was one particular oxygen sensor that was not the O2 sensors others were only assuming. Reread those posts to see what your emission test station may have also confirmed.

A diagnostic port is only reporting on what sees symptoms. It does not report what is wrong - as your $2+K mechanic probably has done. Due to marginal operation of a first oxygen sensor, then other following oxygen sensors (after the cat converter) may be reporting symptoms of that defect.

This is only hard if others assume a diagnostic message actually reports a problem. Diagnostic message about the cat converters never said those are defective. Only said what is coming out is incorrect - only reported a symptom. Use the OBD2 to read voltages from that O2 sensor - which is not the one reporting an error. And answer all previous questions including those from last month.

OK... no reproach intended

Yes, it does.

On the other hand, I don't believe that a dealership is going to resell this vehicle for anything but scrap. At this level, what they are really doing is mentally figuring the cost difference as just a discount on the car I'm buying, and taking possession of the trade-in as a convenience. But if I don't have that "valid" trade-in, it will be harder to negotiate the same discount they could have given me anyway.

You crack me up, tw. Seriously. When the OBDII reader gets here (5-8 business days with FREE SUPER SAVER SHIPPING,) I'll see if I can figure out how to get it to report a voltage number for both O2 sensors. Just for you, because you made me laugh.

Those many previous questions required no ODB2.

For example. Start the car. Drive it on a fixed course that includes one spot where you literally floor it. Do not turn off the engine until you are right back where you started. Repeat that at least three times. Its computer might seea a same failure all three times. But does not report some failures until you have driven it the exact same way after each new restart.

Asked were other important questions such as how an emissions test was performed. By connecting to the computer diagnostic port? By using an exhaust pipe wand? What were numbers for each pollutant? Also important information. And did not require an ODB2.

I don't have the CarPro scanner, the check engine light is currently my only method of failure reporting. Right now, the light is already on. It does not go off without being manually reset.

We didn't watch it happen. It was done however your average state inspection place does it. We didn't get any numbers, we just got a piece of paper indicating that it passed the state inspection threshold (which I am told is somewhat lower than the check engine light threshold.)

stay tuned. there will be another job posted in my projects thread.

Because plt is the coolest and most awesomest person in the world!