P0420 and bad oxygen sensors

"Scott Dorsey" > wrote in message
...
> Jeff Strickland > wrote:
>>
>>And, to clear up an important detail, I thought my CAT was clogged. My
>>fuel
>>mileage went into the dumper and the power fell off even more. I had every
>>indication of a motor that could not breathe, and I suspected the CAT as
>>the
>>problem. It turn out the muffler has dozens of baffles and stuff inside,
>>and
>>something came apart and blocked the passages that the exhaust goes
>>through.
>>
>>The CAT that failed the encounter with a hammer was having a connection
>>problem, the clamps would not hold because there was not enough bite, I
>>sought to enlarge the hole so the pipes would fit together deeper. The
>>plan
>>was a good one, the execution was bad. Oh well ...
>>
>>So, my position is that the CAT is very robust, and not a likely failure
>>item. If the sensor reports a failure of the CAT, my money is on the
>>sensor
>>first, and the CAT second.
>
> Okay, we have a problem here. There are basically two kinds of converter
> problems. First of all we have problems that actually block the exhaust
> line, which are the kind you're talking about. And those problems, as you
> note, are pretty rare.
>
> But there are other converter failures, where the converter no longer is
> effective at reducing emissions. If you have an older car and you live in
> a state that doesn't do emissions testing, you'll never know when these
> failures happen. And sadly, they happen all the time.
>
> If you have a newer car with a second O2 sensor on the output of the
> converter, and the converter fails, you'll get an error message saying
> that the converter has failed. And if you are in a state with emissions
> testing, you'll be told you didn't pass the test.
>
> You'll find if you look that the average lifespan of a converter is
> somewhat
> short of 100,000 miles, but that they mostly fail in such a way that you
> aren't noticing.
> --scott
>



It is my humble opinion that this type of problem -- loss of
effectiveness -- is rare. I would suggest that a CAT should last the life of
the car for the vast majority of owners. Yes, the CAT might fail, but I
suggest that the first thing to fail will be the sensor.

The sensor is a relatively fragile device that lives in a hostile
environment. The sensor will fail before the CAT.

I've not heard of a lifespan for a CAT. I drove a '94 BMW until it read
225,000 miles and was hit by another driver. I have a current '94 BMW with
over 130,000 miles and the CAT is strong. My daughter has an '00 BMW that is
quickly approaching 150,000 miles and the CAT works good. I have a '97 F150
with 110,000 miles and no problems with the CAT. Every car I own has more
miles than you suggested as the life of the CAT. Nobody in my family has
ever bought a CAT, and the only CAT I've bought was to replace the one that
I badly deformed while trying to correct an unrelated exhaust system
problem.

I'm not sure there is a stated life for a CAT, and I seem to recall reading
that they want the CAT to be a life item for the car that it is installed
in. As far as I know, the only thing that can happen, short of physical
damage -- the seams opening, that sort of thing -- is that the operator can
feed the vehicle's fuel supply some kind of product that is not good. I
don't know what not to feed a CAT, other than leaded gasoline, which I don't
even know where one could buy that anymore. I suppose there's a possibility
that aviation gas might be leaded -- but I don't know one way or the
other -- and it could be put into a car.

My advice is that if one gets a Failed CAT Code from the OBDII system, test
and replace the sensor before suspecting the CAT itself as a failure item.

The OBD II system has a sensor that looks specifically at the CAT, but the
actual failure item is the sensor itself, and the OBD II system has not got
a means of checking and evaluating the sensors themselves. Any code that
involves a sensor in the exhaust stream is likely to be caused by the sensor
itself, not the hardware that the sensor is looking at.

Jeff Strickland > wrote:
>
>It is my humble opinion that this type of problem -- loss of
>effectiveness -- is rare. I would suggest that a CAT should last the life of
>the car for the vast majority of owners. Yes, the CAT might fail, but I
>suggest that the first thing to fail will be the sensor.

Could be, but how would you know?

>I've not heard of a lifespan for a CAT. I drove a '94 BMW until it read
>225,000 miles and was hit by another driver. I have a current '94 BMW with
>over 130,000 miles and the CAT is strong. My daughter has an '00 BMW that is
>quickly approaching 150,000 miles and the CAT works good. I have a '97 F150
>with 110,000 miles and no problems with the CAT.

How do you know any of the converters are good? Are you in a place where
you are getting annual emissions testing?

>Every car I own has more
>miles than you suggested as the life of the CAT. Nobody in my family has
>ever bought a CAT, and the only CAT I've bought was to replace the one that
>I badly deformed while trying to correct an unrelated exhaust system
>problem.

I'm sure this is the case, but that's not to say you weren't driving the
car with a completely ineffective converter for hundreds of thousands of
miles.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Wed, 18 Mar 2009 15:17:52 -0500, wrote:

wrote:
>
>>Lots of reasons for cats to fail - and many do. The thing to remember
>>is you need to solve the problem that killed the cat - as they
>>GENERALLY do not die on their own. MANY times a bad O2 sensor will
>>indicate a bad cat - and sometimes it will CAUSE a bad cat.
>
>So how can one remove it permanent and
>still have the car computer control car
>correctly?
>
>I have 2000 Mazda Protege ES with sensor
>before and after cat
Remove what?
On a 2000 you need both sensors and the cat.

"Scott Dorsey" > wrote in message
...
> Jeff Strickland > wrote:
>>
>>It is my humble opinion that this type of problem -- loss of
>>effectiveness -- is rare. I would suggest that a CAT should last the life
>>of
>>the car for the vast majority of owners. Yes, the CAT might fail, but I
>>suggest that the first thing to fail will be the sensor.
>
> Could be, but how would you know?
>

Check the sensor.



>>I've not heard of a lifespan for a CAT. I drove a '94 BMW until it read
>>225,000 miles and was hit by another driver. I have a current '94 BMW with
>>over 130,000 miles and the CAT is strong. My daughter has an '00 BMW that
>>is
>>quickly approaching 150,000 miles and the CAT works good. I have a '97
>>F150
>>with 110,000 miles and no problems with the CAT.
>
> How do you know any of the converters are good? Are you in a place where
> you are getting annual emissions testing?
>

Yes.


>>Every car I own has more
>>miles than you suggested as the life of the CAT. Nobody in my family has
>>ever bought a CAT, and the only CAT I've bought was to replace the one
>>that
>>I badly deformed while trying to correct an unrelated exhaust system
>>problem.
>
> I'm sure this is the case, but that's not to say you weren't driving the
> car with a completely ineffective converter for hundreds of thousands of
> miles.

Except I would fail smog check long before I drove thousands of miles, not
to mention tens, or hundreds of thousands.

On Wed, 18 Mar 2009 14:50:53 -0700, "Jeff Strickland"
> wrote:

>
>"Scott Dorsey" > wrote in message
...
>> Jeff Strickland > wrote:
>>>
>>>And, to clear up an important detail, I thought my CAT was clogged. My
>>>fuel
>>>mileage went into the dumper and the power fell off even more. I had every
>>>indication of a motor that could not breathe, and I suspected the CAT as
>>>the
>>>problem. It turn out the muffler has dozens of baffles and stuff inside,
>>>and
>>>something came apart and blocked the passages that the exhaust goes
>>>through.
>>>
>>>The CAT that failed the encounter with a hammer was having a connection
>>>problem, the clamps would not hold because there was not enough bite, I
>>>sought to enlarge the hole so the pipes would fit together deeper. The
>>>plan
>>>was a good one, the execution was bad. Oh well ...
>>>
>>>So, my position is that the CAT is very robust, and not a likely failure
>>>item. If the sensor reports a failure of the CAT, my money is on the
>>>sensor
>>>first, and the CAT second.
>>
>> Okay, we have a problem here. There are basically two kinds of converter
>> problems. First of all we have problems that actually block the exhaust
>> line, which are the kind you're talking about. And those problems, as you
>> note, are pretty rare.
>>
>> But there are other converter failures, where the converter no longer is
>> effective at reducing emissions. If you have an older car and you live in
>> a state that doesn't do emissions testing, you'll never know when these
>> failures happen. And sadly, they happen all the time.
>>
>> If you have a newer car with a second O2 sensor on the output of the
>> converter, and the converter fails, you'll get an error message saying
>> that the converter has failed. And if you are in a state with emissions
>> testing, you'll be told you didn't pass the test.
>>
>> You'll find if you look that the average lifespan of a converter is
>> somewhat
>> short of 100,000 miles, but that they mostly fail in such a way that you
>> aren't noticing.
>> --scott
>>
>
>
>
>It is my humble opinion that this type of problem -- loss of
>effectiveness -- is rare. I would suggest that a CAT should last the life of
>the car for the vast majority of owners. Yes, the CAT might fail, but I
>suggest that the first thing to fail will be the sensor.
>
>The sensor is a relatively fragile device that lives in a hostile
>environment. The sensor will fail before the CAT.
>
>I've not heard of a lifespan for a CAT. I drove a '94 BMW until it read
>225,000 miles and was hit by another driver. I have a current '94 BMW with
>over 130,000 miles and the CAT is strong. My daughter has an '00 BMW that is
>quickly approaching 150,000 miles and the CAT works good. I have a '97 F150
>with 110,000 miles and no problems with the CAT. Every car I own has more
>miles than you suggested as the life of the CAT. Nobody in my family has
>ever bought a CAT, and the only CAT I've bought was to replace the one that
>I badly deformed while trying to correct an unrelated exhaust system
>problem.
>
>I'm not sure there is a stated life for a CAT, and I seem to recall reading
>that they want the CAT to be a life item for the car that it is installed
>in. As far as I know, the only thing that can happen, short of physical
>damage -- the seams opening, that sort of thing -- is that the operator can
>feed the vehicle's fuel supply some kind of product that is not good. I
>don't know what not to feed a CAT, other than leaded gasoline, which I don't
>even know where one could buy that anymore. I suppose there's a possibility
>that aviation gas might be leaded -- but I don't know one way or the
>other -- and it could be put into a car.
>
>My advice is that if one gets a Failed CAT Code from the OBDII system, test
>and replace the sensor before suspecting the CAT itself as a failure item.
>
>The OBD II system has a sensor that looks specifically at the CAT, but the
>actual failure item is the sensor itself, and the OBD II system has not got
>a means of checking and evaluating the sensors themselves. Any code that
>involves a sensor in the exhaust stream is likely to be caused by the sensor
>itself, not the hardware that the sensor is looking at.
>
>
>
>
>
>
I would suggest that you don;t know what you are talking about. The
sensor that monitors the catalyst is just a second o2 sensor. If the
second sensor tracks the first sensor, the converter is not
functioning. It's that simple. It is possible, but not likely, that
the conveerter could fail in such a way that the sensor would not pick
up the failure, but extremely unlikely that the sensor would indicate
a bad cat if it was functioning properly. Both sensors would need to
fail, and in such a way that they did not cause an O2 sensor failure
code, in order for this to occurr. EXTREMELY unlikely, when you
actually know how they work.

When I say it is POSSIBLE the cat could fail and not be caught by the
sensors, it is because the oxidation catalyst uses up oxygen, and the
reduction catalyst frees up oxygen, but generally not the same amount
each way. The front O2 sensor oscilates with the O2 concentration of
the exhaust gas. When the exhaust is lean, the oxidation catalyst
works making co into co2 and burning off unburned hydrocarbons.- so
the second sensor does not track. When the exhaust is rich the
reduction catalyst works,removing O2 from NOX, making nitrogen and O2.
The O2 is generally stored by the cat to feed the oxidation catalyst,
so the O2 concentration of the exhaust remains more or less constant
at the back sensor. Multiple mode failures in the converter could,
concievably, occur which would provide a relatively constant O2 level
at the rear sensor without fully treating the HC, CO and NOX.

> wrote in message
...
> On Wed, 18 Mar 2009 14:50:53 -0700, "Jeff Strickland"
> > wrote:
>
>>
>>"Scott Dorsey" > wrote in message
...
>>> Jeff Strickland > wrote:
>>>>
>>>>And, to clear up an important detail, I thought my CAT was clogged. My
>>>>fuel
>>>>mileage went into the dumper and the power fell off even more. I had
>>>>every
>>>>indication of a motor that could not breathe, and I suspected the CAT as
>>>>the
>>>>problem. It turn out the muffler has dozens of baffles and stuff inside,
>>>>and
>>>>something came apart and blocked the passages that the exhaust goes
>>>>through.
>>>>
>>>>The CAT that failed the encounter with a hammer was having a connection
>>>>problem, the clamps would not hold because there was not enough bite, I
>>>>sought to enlarge the hole so the pipes would fit together deeper. The
>>>>plan
>>>>was a good one, the execution was bad. Oh well ...
>>>>
>>>>So, my position is that the CAT is very robust, and not a likely failure
>>>>item. If the sensor reports a failure of the CAT, my money is on the
>>>>sensor
>>>>first, and the CAT second.
>>>
>>> Okay, we have a problem here. There are basically two kinds of
>>> converter
>>> problems. First of all we have problems that actually block the exhaust
>>> line, which are the kind you're talking about. And those problems, as
>>> you
>>> note, are pretty rare.
>>>
>>> But there are other converter failures, where the converter no longer is
>>> effective at reducing emissions. If you have an older car and you live
>>> in
>>> a state that doesn't do emissions testing, you'll never know when these
>>> failures happen. And sadly, they happen all the time.
>>>
>>> If you have a newer car with a second O2 sensor on the output of the
>>> converter, and the converter fails, you'll get an error message saying
>>> that the converter has failed. And if you are in a state with emissions
>>> testing, you'll be told you didn't pass the test.
>>>
>>> You'll find if you look that the average lifespan of a converter is
>>> somewhat
>>> short of 100,000 miles, but that they mostly fail in such a way that you
>>> aren't noticing.
>>> --scott
>>>
>>
>>
>>
>>It is my humble opinion that this type of problem -- loss of
>>effectiveness -- is rare. I would suggest that a CAT should last the life
>>of
>>the car for the vast majority of owners. Yes, the CAT might fail, but I
>>suggest that the first thing to fail will be the sensor.
>>
>>The sensor is a relatively fragile device that lives in a hostile
>>environment. The sensor will fail before the CAT.
>>
>>I've not heard of a lifespan for a CAT. I drove a '94 BMW until it read
>>225,000 miles and was hit by another driver. I have a current '94 BMW with
>>over 130,000 miles and the CAT is strong. My daughter has an '00 BMW that
>>is
>>quickly approaching 150,000 miles and the CAT works good. I have a '97
>>F150
>>with 110,000 miles and no problems with the CAT. Every car I own has more
>>miles than you suggested as the life of the CAT. Nobody in my family has
>>ever bought a CAT, and the only CAT I've bought was to replace the one
>>that
>>I badly deformed while trying to correct an unrelated exhaust system
>>problem.
>>
>>I'm not sure there is a stated life for a CAT, and I seem to recall
>>reading
>>that they want the CAT to be a life item for the car that it is installed
>>in. As far as I know, the only thing that can happen, short of physical
>>damage -- the seams opening, that sort of thing -- is that the operator
>>can
>>feed the vehicle's fuel supply some kind of product that is not good. I
>>don't know what not to feed a CAT, other than leaded gasoline, which I
>>don't
>>even know where one could buy that anymore. I suppose there's a
>>possibility
>>that aviation gas might be leaded -- but I don't know one way or the
>>other -- and it could be put into a car.
>>
>>My advice is that if one gets a Failed CAT Code from the OBDII system,
>>test
>>and replace the sensor before suspecting the CAT itself as a failure item.
>>
>>The OBD II system has a sensor that looks specifically at the CAT, but the
>>actual failure item is the sensor itself, and the OBD II system has not
>>got
>>a means of checking and evaluating the sensors themselves. Any code that
>>involves a sensor in the exhaust stream is likely to be caused by the
>>sensor
>>itself, not the hardware that the sensor is looking at.
>>
>>
>>
>>
>>
>>
> I would suggest that you don;t know what you are talking about. The
> sensor that monitors the catalyst is just a second o2 sensor. If the
> second sensor tracks the first sensor, the converter is not
> functioning. It's that simple. It is possible, but not likely, that
> the conveerter could fail in such a way that the sensor would not pick
> up the failure, but extremely unlikely that the sensor would indicate
> a bad cat if it was functioning properly. Both sensors would need to
> fail, and in such a way that they did not cause an O2 sensor failure
> code, in order for this to occurr. EXTREMELY unlikely, when you
> actually know how they work.
>
> When I say it is POSSIBLE the cat could fail and not be caught by the
> sensors, it is because the oxidation catalyst uses up oxygen, and the
> reduction catalyst frees up oxygen, but generally not the same amount
> each way.


I know what the sensors monitor.

What I said was that there is no sensor to monitor the sensors. The sensors
send false data, particularly in the case of the O2 sensors _because_ the
environment that these sensors operate in is very hostile. Given the
specific code being discussed, P0420, all I'm saying is that the sensor is
more likely a failure item than the CAT.

I'm not looking at a CAT failure that is not reported, I'm looking at a
reported CAT failure that does not really exist.

We HAVE a code. It specifically points to the after-CAT sensor because the
code that is generated can never happen from an upstream sensor.

We have a false report of an very costly item failing. That's my story, and
I'm sticking to it.

wrote:

>>I have 2000 Mazda Protege ES with sensor
>>before and after cat
> Remove what?
> On a 2000 you need both sensors and the cat.


remove the cat

> wrote in message
...
> wrote:
>
>>>I have 2000 Mazda Protege ES with sensor
>>>before and after cat
>> Remove what?
>> On a 2000 you need both sensors and the cat.
>
>
> remove the cat

Why do you want to remove the cat?
--

Ray O
(correct punctuation to reply)

"Jeff Strickland" > wrote in message
...
>
><snipped> I'm not looking at a CAT failure that is not reported, I'm
>looking at a reported CAT failure that does not really exist.
>
> We HAVE a code. It specifically points to the after-CAT sensor because the
> code that is generated can never happen from an upstream sensor.
>
> We have a false report of an very costly item failing. That's my story,
> and I'm sticking to it.
>
>
We've been through this before.

Your premise that the code that is generated can never happen from an
upstream sensor is incorrect. P0420 is generated IF the signal from sensor
#2 (post-cat) looks like the signal from sensor #1 (upstream sensor). When
the system is warmed up, the signal from S1 oscillates, and on an
oscilloscope, looks something like a square wave because the oxygen content
in the exhaust gas is oscillating. After the exhaust passes through the
cat, the O2 content in the gas is evened out so that the signal that S2 puts
out has less variance in amplitude (height of the wave) and frequency
(number of waves per minute) and so the signal from S2 looks different from
the signal from S1.

If the cat is bad, or if you took the cat out of the system and replaced it
with a piece of pipe, the O2 content doesn't get evened out and so the
signal from S2 looks like the signal from S1. IOW, the signal from S2 looks
dead if the cat is working and looks lively when the cat is not working. If
the ECU sees a lively signal, that means the cat isn't working and it sets
P0420.

If you get P0420, it is a good idea to check the sensors because it is easy
to check, they generally have a shorter life than a cat, a sensor is cheaper
than a cat, and a bad S1 can cause premature cat failure, but the cat should
also be changed because the likelihood of a false P0420 is almost nil.
--

Ray O
(correct punctuation to reply)

"Ray O" > wrote:

>>>>I have 2000 Mazda Protege ES with sensor
>>>>before and after cat
>>> Remove what?
>>> On a 2000 you need both sensors and the cat.
>>
>>
>> remove the cat
>
>Why do you want to remove the cat?

Cause I don't have the money to replace it