How could 50 to 100 clearings of the OBD codes (using a dumb OBD reader) cause the catalytic I/M readiness monitor to set after months of not setting?
Can the complicated electronics modules be "saving" scores of prior memory sessions perhaps?
The storey is a bit confusing because the pieces only fell in together well after the fact for each event, but here's the short summary of what happened as I loosely recall the major happenstances of this purely electronic ordeal.
[1] The check engine light has been on, on the dash, almost constantly [2] Mostly when I looked, it would be P0420 bad cat pending & set codes [3] I've been going through this regimen now, for about five or six years [4] I didn't need smog for more than a year so I didn't worry about codes [5] When it came within months of smog time, I cleared the OBD codes [6] Mostly either the code comes back or the readiness monitor won't set [7] But once in a while, the readiness monitor does set so I rush to smog [8] I did that - it passed smog - but failed for a hose in bad condition [9] I painted the hose black so that it would look like it's brand new [10] But then for another month I couldn't get the readiness monitor to set [11] At one point, I accidentally added gasoline with water (long story) [12] The car ran like hell for an entire gas tank until I refilled it
After that, it passed smog and for months now, no codes. What happened? I have no clue.
A miracle? A coincidence?
I do not know.
Maybe what "might" have happened is that during the time that I was driving on the tank of watery gas, I had to keep the OBD code clearer on my lap.
Within a mile, the engine would stumble and I'd clear the codes and the engine would run fine for another mile, and then it would stumble, and then I'd clear the code and it would run fine for another mile, and so on.
This I did for at least a hundred, maybe two hundred maybe three hundred times during the watery gas stage - but - miracles to happen I guess because after that, no codes and, get this, the readiness monitors all set.
I passed at a different smog station (with the painted hose to make it look like new not being an issue) and now I'm just wondering what the heck happened?
Can it be that there is some kind of multiple instance "persistent memory" inside one of the engine computers that I finally wiped out by clearing the codes hundreds of times in a row?
You left out the name and year of the vehicle. You're asking people to diagnose an apparently intermittent problem. Those are difficult to find even for someone with the proper equipment and access to the vehicle to diagnose. It could be a bad connection in a wiring harness for all I know. Best of luck in finding an answer. Do you know the song Blowing in the Wind by Peter, Paul, and Mary?
It cannot. But the fact that you've got 50 to 100 clearings of the OBD codes makes your general maintenance process very suspect.
What this means is that the O2 sensor downstream of your converter is reading an incorrect value. This could mean your converter is bad, or maybe that the O2 sensor is bad, or maybe that the connector is bad.
If other codes were set too, it could have been all kinds of other things. If you're seeing incorrect values on both pre and post converter sensors, you'll see other codes, and that could be the result of all kinds of misfiring issues or mixture control issues.
Have you considered actually finding and fixing the problem instead of constantly resetting the error? You're not doing your engine or your gasoline bill any good this way.
Wow, with maintenance like that it's a wonder your car runs at all.
Maybe the converter was dirty and all the steam cleaned it out. Maybe you had a fouled plug which was causing a misfire and the steam cleaned it up. Maybe you had a bad vacuum hose and the warmer weather caused it to seal up.
Since you didn't actually find the problem when you had the code coming up, and you made no attempt to do actual diagnosis, it's hard to tell after the fact.
As my father always said, "machines that fix themselves always break themselves again."
You are too fixated on the codes popping up and making no attempt to ask WHY the codes were popping up and what was actually going on. Stop worrying about the damn codes and start worrying about how the engine is running.
That's what I would suspect, over the repeated clearing of the codes doing it. The water could have also altered the readings of the O2 sensors. If it's from the water, the effect is likely temporary. Also I would think it might be possible that it's bad O2 sensors and not the catalytic converter. If they are past 100K, that might be the place to start.
That's a good question. Is there some chemistry that running water through the cat cleans it up?
The water issue was new as that was a complete accident that I had an empty tank and I had to take someone to the airport all of a sudden so I used a five gallon container of gas that was outside and it turned out to be old and it happened to have a lot of water in it as the cap was leaking inward.
The 2004 Mitsubishi Lancer 4-cylinder tiny engine has always had this problem since I bought it as the previous owner sold the entire car to me for $200 knowing it needed a new catalytic converter & much other stuff.
A mechanic told him that was the reason for the P420 code, but what I did when I got the car was put a new oxygen sensor in and that helped for a couple of years to get it through smog but it still is hard to set the readiness monitors. I know all about the drive cycle but it's got nothing to do with that as it takes months of use to set the readiness monitors.
Only two things have ever set the readiness monitors for me, one of which was to drive for a few hundred miles at one stretch, and back, which shouldn't do anything (because I know what a drive cycle entails).
The other thing happened to be the water in the gasoline fiasco, where the tank is something like ten or so gallons, but I put in five gallons of a gas:water mix, which I used up and then refilled with clean gasoline.
Once the codes see a misfire of 1 in 200 revolutions, the engine control module turns off the electricity to that spark plug, and the only way to turn it back on is either to shut down the car or reset the codes.
It turns out that clearing the codes while driving works perfectly. There is a seven second delay between stumbling, clearing, and the codes gone.
I know this because I had the OBD tester in my lap for hundreds of miles over a period of a couple weeks where I reset the code I don't know how many times, but probably a few hundred times in a single tank of gas.
What's weird is that this issue of the P0420 cat code and the inability to reset the cat read monitor has happened for many years (probably three smogs, so that's six years) but its character changed completely after the water-in-the-gas fiasco with the hundreds of reset actions.
Now there is no P0420 code and the readiness monitor set it self nicely. How did that happen?
I was thinking that there might be a database inside the engine control modules of the last fifty or so codes, where I used them all up by clearing more than those fifty or so times, but your idea that the water in the gas chemically cleaned out the cat sounds better as it's kind of like a 'seafoam' treatment, of sorts.
Is there any chemistry backing up that idea that the water cleaned the cat?
The question isn't about how horrible a person I am but whether or not running gas:water could have (probably temporarily) increased the efficiency of an old cat (or whether clearing an engine control unit buffer could have enabled the cat readiness monitor to be more easily set).
As for your negative comment about my maintenance skills, I must not have been clear although I thought I was detailed enough with the dozen steps listed. I don't care about the cat efficiency unless I have to smog.
Then, all of a sudden, I care about two things [1] I care that there are no pending or set codes (especially P0420) [2] I care that the readiness monitors are set (especially the cat)
You don't seem to know engines well, so allow me to explain that when the engine sees a misfire in 1 out of 200 revolutions (most cars), the engine control module permanently shuts down the spark to that cylinder (to protect the cat).
This is permanent.
[1] The engine is running but at some point the engine noticeably stumbles [2] The CEL goes on and the cylinder will be off forever [3] Even if you drive for the 300 miles or so that the gas tank can do
There are only 2 things that will undo that permanently shut off cylinder. [1] Either you turn the engine off and start it back (in which case the code is still there but the spark is back again) [2] Or you clear the codes (in which case the code is gone and the spark is back to that cylinder)
Then the cycle repeats anew.
This is well known so if you don't know it you just don't know engines well and that's fine because this question is about the cat and not the engine.
Could the water:gas mixture, somehow, have increased the cat efficiency? Could the hundreds of code clearings, somehow, have wiped out a buffer?
When I got the Mitsubishi Lancer 2004 for $200 it had this problem then. I replaced the oxygen sensor (there appears to only be one upstream sensor) and that alone fixed the problem for the first smog about 5 or 6 years ago.
There are no oxygen sensor codes. I need to repeat that because the oxygen sensor is not showing any codes.
That means the oxygen sensor is getting the correct voltage, the wires are fine (although there could be an intermittence I guess), and the input and output are fine.
I repeat there are no oxygen sensor codes. Therefore, I see no reason to suspect the oxygen sensor on a mere whim.
I've noticed a lot of people replace the sensor whenever they get a code but that's what the tests are for on the sensor itself. If the sensor were bad, it would show a code of a bad input, output, or power connection.
It doesn't.
It's only the P0420 and there is only one bank so it's for the cat.
"The P0420 code signals a low catalyst system efficiency. This code suggests that the oxygen levels are below the desired threshold (Bank 1), which most often results from problems with your car's exhaust or fuel systems."
I'm sure it's the cat. I just don't want to replace the cat.
And, get this, it passes smog without me doing anything but clearing the P0420 code and letting the readiness monitors (especially for the cat) set.
The problem isn't passing smog because it generally took a few months of driving to finally set the readiness monitors after clearing.
The question is only whether clearing the codes hundreds of times allowed some kind of "buffer" to be wiped out in the engine control module - or - as someone else suggested - maybe the water in the gas increased the efficiency (somehow? chemically?) of the catalytic converter?
There is no problem other than the cat is the original 2004 and it has low efficiency, and, as a result, every once in a while the P0420 pops up and the readiness monitor for the cat takes hundreds of miles for it to set.
There was absolutely nothing wrong with the hose & it's expensive to replace. It passes smog. It would have cost about $100 bucks to replace.
Painting it accomplished essentially the same function as replacing it given there was nothing functionally wrong with the hose at that time.
It just didn't pass a visual inspection. I would have passed it. He didn't. He wanted me to do a repair right then and there at his gas station.
I refused. I think he just wanted business by claiming the hose was bad. There was nothing I could do other than pay him and never go back there.
There was nothing wrong with the hose from a functional standpoint. If it actually fails, then I'll replace it. But I'll wait for it to fail.
It doesn't seem like you understand engines at all by the comments you're making. This is a car that cost $200 five or six years ago. Not a Tesla.
It has an old 2004 tired low efficiency catalytic converter. That's all.
If I'm not going to replace a hose that isn't broken, I'm certainly not going to replace a catalytic converter that isn't broken either.
It passes smog. It just throws a low efficiency code for the cat.
Once in a while.
I don't think you understand engines as there couldn't possibly have been a "fouled plug" as that's just shooting in the air hoping to hit the moon.
It's not a vacuum hose either as that would have thrown a different code. Probably a P0171 or similar lean engine condition which is a common fault.
If you keep shooting at the moon, you might hit it, but that's not the kind of guesses I was hoping to get as to how either the hundreds of resets alone, or the bad gas alone, or the combination, caused the apparently (probably temporary) fixing of a low efficiency catalytic converter code.
You never asked me what diagnostics I've run, where I _believe_ that the code is telling me the truth, which is that the cat is low efficiency at intermittent stages.
You're just shooting at the moon hoping you'll hit it while I'm believing EVERYTHING the car is telling me. The OBD codes are telling me that the cat is low efficiency sometimes and I believe it. Why wouldn't I believe it?
It's not the oxygen sensor as I replaced it and I tested the old one with a burner flame and it read in the range that was to be expected of it.
I don't know why I have trouble setting the readiness monitor for the cat, but I "suspect" (yes, I am assuming) that it's due to the low efficiency.
I think you missed the part about that being caused by water in the gas. The water, if that's what cleaned out the cat, turned out to be a boon.
I find it incredulous that you think I'm fixated on the "codes popping up", where I'm _believing_ everything the codes are telling me. Everything.
[1] The cat, sometimes, is low efficiency [2] The cat readiness monitor, after clearing, takes a long time to set
I believe exactly what the codes are telling me. I did all the diagnostics long ago and there's nothing to do but replace the cat if I cared about the low efficiency and readiness monitors.
The only time I care about either of them is when I need to pass smog. Which I _always_ do pass - except when the hose looks ugly that is.
The question here isn't how horrible a person I am and how great you are. The question is simply what caused the complete change of character.
Did the water in the gas have any chance of chemically "cleaning" out the cat such that it suddenly became more efficient (probably temporarily) as one person suggested?
Or, maybe did just clearing out the buffer of fifty or so prior codes stored in the engine control module enable the readiness monitor to be set?
You seem to be right at the inflection point of the cat efficiency, so almost anything that affects its efficiency will cause your symptoms.
That means your real question, whether you know it yet or not, is what can increase/decrease the efficiency of a catalytic converter in operation?
Taking your long drive example, I think that long drive might have heated the cat to the point that maybe that heat temporarily increased its chemical efficiency. Maybe the same thing happens with water in the gas?
Or, maybe it's not the water in the gas but the fact that the water caused the cylinder to shut off which caused gas to flow over the cat which might have again heated up the cat enough to temporarily increase its efficiency?
You only threw a little gas onto the cat because you kept resetting the codes so you threw gas on the cat, and then you ran normally hot, and then you again threw gas on the cat, & you repeated that cycle many times over.
Maybe that heat:cool:heat:cool:heat:cool:heat:cool cycle increased the efficiency of the cat just enough over a threshold to stabilize the system?
All indicators are that you're on the cusp of catalytic efficiency, where
98% of the time or thereabouts you're just efficient enough, but under some conditions that you need to figure out (usually temperature & humidity), you're below efficiency.
Then the code is set which will reset on its own within three drive cycles. But once you clear the code, you have to wait for cat readiness to be set.
If you have the time for your next smog, I suggest you do NOT clear the codes (because then you add the second readiness monitor to the mix), but that you let the drive cycle (usually around 50 miles) clear it for you.
Technically, you only need to replace the front of the cat, not the back. (:->)
You can narrow down the problem even further by knowing that only the NOx "light off" brick in the front of the cat is monitored by the OBD system.
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That "light off" brick stores oxygen it separates from the NOx vapors. The HC/CO catalyst brick behind it is not monitored by the OBD system.
So your problem is probably limited only to the front NOx section alone.
"The Upstream O2 signal switches very rapidly in response to Fuel Trim (several times a second). The O2 sensor behind the light-off catalyst (the Downstream Sensor) is also monitoring oxygen, but if the light-off (NOx) catalyst is storing oxygen properly (meaning the catalyst is healthy), the rear O2 sensor signal will be very lazy when compared to the upstream O2. When the ECM/PCM sees the downstream O2 sensor switching at or near the same rate as the upstream O2 sensor, it sets the P0420 code."
To do its job, the front "light off" NOx catalyst brick has to be hot. And it has to be able to store enough oxygen to add it to the NOx vapors.
If anything you did makes that front NOx "light off" brick get hotter or store more oxygen, then you'd be experiencing the effect that you've seen.
Certainly. All that steam in there could have cleaned the converter out. But it ALSO could have cleaned out the downstream O2 sensor. And it might have temporarily cleaned something completely unrelated too.
No.
You have a downstream sensor, and you know that because you got a P0240.
Check what the P0240 code means. It means that the downstream O2 sensor is not getting the correct value. Since you aren't getting any other codes, you can assume the upstream O2 sensor is getting the correct value, and that the engine stoichometry is good but that the gas coming out of the converter is not good.
That is why the P0240 sensor implies a bad converter.
How bad is the converter? Is the issue the converter itself or the measurement? The code does not tell you. If you have a proper scanner you can look at the actual values of the oxygen sensors. You can see that they are in range, that they are settling in quickly, and how well they track one another. This is how you determine whether it's a sensor or the converter or both.
If you do not have a proper scanner you are working blind and all you can do is measure the converter temperature with an IR thermometer and make sure it's getting up to temperature properly. If it's too cold, it's not working. This is a very crude measurement.
The P0240 -is- a downstream oxygen sensor code.
The P0240 -is- a downstream oxygen sensor code.
The P0240 -is- a downstream oxygen sensor code.
It's likely the converter, yes, and you should almost certainly replace it, but first verify that it's not working by looking at the actual values.
Likely it's working right now but is marginal... actual measurements will tell you for sure.
Do you have the smog numbers? The numbers are also an indication of how marginal things really are.
That sounds like a problem to me, and one that isn't that awful to fix with a generic replacement.
On 23 Apr 2023, PietB <www.godfatherof.nl/@opt-in.invalid> posted some news <news:u23t4e$3tosi$ snipped-for-privacy@dont-email.me:
I don't know if hotter is better, but certainly the cat has to be at least hot enough to reduce the nitrogen oxides by adding oxygen to them.
This video for my Chevy talks about catalytic converter cleaners, which, if that works, must be doing something chemical to the platinum plated screen.
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For my Chevy, they suggest either removing the cat and soaking in detergent for 10 hours, or pouring LiquiMoly catalytic system cleaner & driving it.
When I looked up what the LiquiMoly did though, it only says that it prevents soot from getting into catalytic converer in the first place.
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The video explains the detergent method cleans out the honeycomb screens.
That video also covers extending the oxygen sensor away from its mount but if they're going to visually inspect all your hoses, they'll see that too.
It could be that your watery gas somehow cleaned out the screen honeycomb?
It could be the steam that cleaned the platinum based metal group screens. Or maybe the fuel mixture was lean enough to heat the grids to burn soot?
Might be based on this which says that the efficiency is calculated over a period of time from many measurements under many conditions.
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"For a catalyst efficiency code like P0420 to be set, a number of criteria must be met. For example, the oxygen or air/fuel ratio sensors must see a reduction in efficiency of the converter. In other words, the oxygen levels before and after the converter, they don't change or they're not within the specified levels, well, it's going to set a code.
But it is not an automatic pass or fail. The oxygen sensors need to see this loss in efficiency over a number of drive cycles and under certain conditions. This is why it might take a few hours or even a few days for the light to come back on after you clear that efficiency code, and this is why it may take time for that code to come back.
The converter has an efficiency rating that is computed by the Engine Management System. This number rates the amount of reduction that is occurring in the converter and its ability to even store oxygen. But the efficiency of the converter is tied to the fuel trim of the engine.
Most engines will minutely alter the short-term fuel trim to replenish oxygen in the converter to add fuel or reduce the amount of fuel. This helps to keep the converter in the correct temperature range to achieve the most efficient operation."
I think he said a P0420 but you probably just transposed the numbers as that's an efficiency code.
Not really. It's a comparison of the upstream to downstream code.
I'd like to see them also.
There's nothing wrong once he clears the code. It could be he changed the calculus for the catalytic efficiency numbers by zeroing out the codes a lot given it stores them for at least a few days according to the article.
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It could be that by eliminating the previous efficiency calculus, he starts with a baseline efficiency calculus which is exactly what he has.
So there can't be a loss of efficiency if he gets to determine the current efficiency by zeroing all the codes out a hundred times.
Clever if that trick works twice because you get to determine the baseline efficiency, instead of letting the ECM/PCM determine its own efficiency.
Right. And we don't know what the integration time is, but we can guess at what it is by how long it was taking for the code to come back before. That time has been exceeded now.
There's nothing *to set a new code* wrong once he clears the code. That does not mean that there is nothing wrong. You need to see the numbers in order to know if something is wrong.
Yes, but how long will it take to recalculate? I would not expect it to be very long, and previous resets didn't do this.
But really, until we see actual numbers, all anyone can do is guess blindly.
On 23 Apr 2023 20:42:44 -0000, Scott Dorsey wrote:
If the mixture is rich it depletes the oxygen but if it's run lean, the oxygen is added back, so I'm leaning toward a half tank of lean fuel.
This says the efficiency calculations is not octane dependent where adding the water maybe monetarily raised the octane rating inside the cylinder.
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This says you might be able to regenerate the oxygen to improve the catalytic efficiency (CE) by the use of oxalic acid & citric acid.
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[1] "Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and Citric Acid Washing" by S.Y. Christou, H. Birgersson, J.L.G. Fierro, A.M. Efstathiou, Environmental Science and Technology. 40 (2006) 2030-2036. The abstract for this article states: "The efficiency of dilute oxalic and citric acid solutions on improving the oxygen storage capacity (OSC) and catalytic activity of a severely aged (83,000 km) commercial three-way catalyst (TWC) has been investigated. Washing procedures applied after optimization of experimental parameters, namely, temperature, flow-rate, and concentration of acid solution, led to significant improvements of OSC and catalytic activity (based on dynamometer test measurements) of the aged TWC. The latter was made possible due to the removal of significant amounts of various contaminants accumulated on the catalyst surface (e.g., P, S, Pb, Ca, Zn, Si, Fe, Cu, and Ni) during driving conditions, as revealed by Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and X-ray Photoelectron Spectroscopy (XPS) analyses. For the first time, it is demonstrated that dilute oxalic acid solution significantly improves the catalytic activity of an aged commercial TWC toward CO, CxHy, and NOx conversions under real exhaust gas conditions (dynamometer tests) by two to eight times in the 250−450 °C range and the OSC quantity by up to 50%. Oxalic acid appears to be more efficient than citric acid in removing specifically P- and S-containing compounds from the catalyst surface, whereas citric acid in removing Pb- and Zn-containing compounds, thus uncovering surface active catalytic sites."
Everything I've read says it takes a few drive cycles which can take days but we don't really know yet how much integration time the PCM uses for CE.
The PCM could save the CE for years for all we know about how this works.
I found a lot of articles that said it takes "40 drive cycles" though.
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"Any time the MIL lamp is on, the cause should be investigated - the sooner the better. Ignoring it will not make it go away - unless the fault does not recur in three consecutive drive cycles that encounter the same operating conditions, or the fault is not detected for another 40 drive cycles. If OBD II sees no further evidence of the problem it will turn off the MIL lamp and erase the code."
I'm not sure why it takes 40 full drive cycles, as that's something like a few hundred days up to an entire year if you know how drive cycles work.
But when I added "40 drive cycles" to the search, I got lots of hits. But they all seem to be a copy of the same words, so you never know.
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"With some exceptions, the OBD II warning lamp will also go out if a problem does not recur after 40 drive cycles."
If one drive cycle takes days, and about 50 miles, 40 will take forever. Maybe he cleared all that garbage when he cleared the codes >40 times?
I don't think there will be any numbers for states using the OBD test only.
I searched for details on how the catalytic efficiency (CE) is determined but I haven't found anything other than generic percentages reported.
I would like to see the numbers but alas they likely won't exist if the smog test is just an OBD check since an OBD check doesn't measure anything.
There was no backfiring but lots of stammering which cleared the moment I reset the codes, so the palpable stammering was caused by shutting down the cylinder due to non-palpable misfiring due probably to a non-stoichiometric air:fuel ratio due to the water in the gasoline.
I went to my glovebox to get the smog report but it doesn't show any values. It just says the following in a chart & gives certificate serials.
Air Injection System = NA Catalyst = pass Computers, sensors, switches & wiring = pass Crankcase emission controls = pass Exhaust gas recirculation (EGR) = pass Fuel evaporation system (EVAP) = pass Fuel metering system = pass Liquid fuel leak check = pass OBDII = pass Other emission related components/systems = pass Smoke check = pass Turbocharger/supercharger = NA Vacuum lines to sensors/switches = pass
I think I found out why the readiness monitors were hard to set but I'm still researching that so I'll write that up separately for review.
I'm looking for how they electronically determine catalytic converter efficiency to compare the old values with the new values.
Most cites are general purpose and they also say wrong things since we know that only the NOx matters at the front of the cat, not HC or CO emissions.
This reference explains a bit of the complexity of what it takes to set the readiness monitors where what it says is that it's not just a simple thing.
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"If there are any efficiency or related codes stored or even a pending diagnostic trouble code, they can prevent a monitor from ever running or completing."
I wonder if there is even one inefficient code stored in the 40 stored drive cycle results that this is what is preventing the readiness monitors from being set?
That reference also said there are other gotchas on when a readiness monitor will be set, for example, the fuel level apparently matters. "Be sure that you have enough fuel in the car. Some monitors, for instance the EVAP monitor, may require the fuel level to be between 35% and 85% to initiate the diagnostic testing."
The reference specifically calls out the problem of setting readiness monitors when the catalytic converter efficiency is in question. "any time you're troubleshooting a catalyst efficiency problem, it's very important to use a scan tool that can tell you if all the readiness monitors have run or not. If one or more monitors are not ready, the vehicle will have to be driven under the correct conditions to make the monitor set. Then, and only then, will you get an accurate diagnosis."
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