P0420 and bad oxygen sensors

That's why owners shouldn't replace catalytic converters without
checking sensors first:

Feb 2009 Motor.com article:
http://www.motor.com/magazine/pdfs/022009_02.pdf

On Sun, 15 Mar 2009 20:25:15 -0700 (PDT), wrote:

>That's why owners shouldn't replace catalytic converters without
>checking sensors first:
>
>Feb 2009 Motor.com article:
>http://www.motor.com/magazine/pdfs/022009_02.pdf


Helps to have a 4 gas analyzer to check the exhaust pre and post cat -
then you KNOW if the cat is working.

Also having a good scanner that can "track" the O2 sensor helps - you
can see what the sensor is doing. Often switching sensors from pre to
post will also tell you if the sensor is the problem. If moving the
sensors still gives the same code, without an o2 sensor code, it id
VERY likely the cat IS week.

A catalytic converter is VERY robust, and unless you feed the car leaded
gasoline or some other unauthorized substance, the CAT ought to last the
life of the car.

The only CAT that I have ever replaced was physically damaged by reason of
losing a battle with a very large hammer. I had an '89 Ford motorhome
(motorhome on a Ford chassis) that I thought had a CAT problem in about
2003. The CAT was fine. The muffler was the problem. The muffler was a
significantly less costly repair. The motorhome is still going strong with
the same CAT that I thought needed replacing back in '03.

I'd not expect any '96 or newer car or truck sold in the USA to have a CAT
problem for several more years.

The sensors, on the other hand, are not nearly so robust and the environment
they live in is very hostile. I'd suspect a sensor failure long before a CAT
problem.




> wrote in message
...
> That's why owners shouldn't replace catalytic converters without
> checking sensors first:
>
> Feb 2009 Motor.com article:
> http://www.motor.com/magazine/pdfs/022009_02.pdf

"Jeff Strickland" > wrote in message
...
>A catalytic converter is VERY robust, and unless you feed the car leaded
>gasoline or some other unauthorized substance, the CAT ought to last the
>life of the car.
>
> The only CAT that I have ever replaced was physically damaged by reason of
> losing a battle with a very large hammer. I had an '89 Ford motorhome
> (motorhome on a Ford chassis) that I thought had a CAT problem in about
> 2003. The CAT was fine. The muffler was the problem. The muffler was a
> significantly less costly repair. The motorhome is still going strong with
> the same CAT that I thought needed replacing back in '03.
>
> I'd not expect any '96 or newer car or truck sold in the USA to have a CAT
> problem for several more years.
>
> The sensors, on the other hand, are not nearly so robust and the
> environment they live in is very hostile. I'd suspect a sensor failure
> long before a CAT problem.
>

Pre OBD II vehicles generally did not have a post-cat O2 sensor so there was
no on-board way for the vehicle's diagnostic system to evaluate the
performance of the cat so you would not get a check engine light related to
cat performance. The only way to evaluate cat performance in a pre-OBD II
vehicle is with an exhaust gas analyzer (also the best way to evaluate cat
performance in an OBD II vehicle).

The catalyst in a catalytic converter does not get used up or wear out so it
could theoretically last forever. What happens when cats fail is that the
catalyst becomes coated with contaminants like particulate (soot) so that
the exhaust gas passing over the catalyst bed does not come in contact with
the catalyst so no catalytic action occurs, or the converter develops a hole
that allows exhaust gas to escape and cool air to enter, or interior
corrosion allows the bed holding the catalyst to collapse or come apart,
clogging the flow of exhaust.

Your motor home probably saw a lot of highway miles, with a nice hot exhaust
that minimized buildup of contaminants on the catalyst, prolonging its life.
--

Ray O
(correct punctuation to reply)

"Ray O" > wrote in message
...
>
> "Jeff Strickland" > wrote in message
> ...
>>A catalytic converter is VERY robust, and unless you feed the car leaded
>>gasoline or some other unauthorized substance, the CAT ought to last the
>>life of the car.
>>
>> The only CAT that I have ever replaced was physically damaged by reason
>> of losing a battle with a very large hammer. I had an '89 Ford motorhome
>> (motorhome on a Ford chassis) that I thought had a CAT problem in about
>> 2003. The CAT was fine. The muffler was the problem. The muffler was a
>> significantly less costly repair. The motorhome is still going strong
>> with the same CAT that I thought needed replacing back in '03.
>>
>> I'd not expect any '96 or newer car or truck sold in the USA to have a
>> CAT problem for several more years.
>>
>> The sensors, on the other hand, are not nearly so robust and the
>> environment they live in is very hostile. I'd suspect a sensor failure
>> long before a CAT problem.
>>
>
> Pre OBD II vehicles generally did not have a post-cat O2 sensor so there
> was no on-board way for the vehicle's diagnostic system to evaluate the
> performance of the cat so you would not get a check engine light related
> to cat performance. The only way to evaluate cat performance in a pre-OBD
> II vehicle is with an exhaust gas analyzer (also the best way to evaluate
> cat performance in an OBD II vehicle).
>
> The catalyst in a catalytic converter does not get used up or wear out so
> it could theoretically last forever. What happens when cats fail is that
> the catalyst becomes coated with contaminants like particulate (soot) so
> that the exhaust gas passing over the catalyst bed does not come in
> contact with the catalyst so no catalytic action occurs, or the converter
> develops a hole that allows exhaust gas to escape and cool air to enter,
> or interior corrosion allows the bed holding the catalyst to collapse or
> come apart, clogging the flow of exhaust.
>
> Your motor home probably saw a lot of highway miles, with a nice hot
> exhaust that minimized buildup of contaminants on the catalyst, prolonging
> its life.
> --

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.

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

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Jeff Strickland" > wrote in message
...
>
> "Ray O" > wrote in message
> ...
>>
>> "Jeff Strickland" > wrote in message
>> ...
>>>A catalytic converter is VERY robust, and unless you feed the car leaded
>>>gasoline or some other unauthorized substance, the CAT ought to last the
>>>life of the car.
>>>
>>> The only CAT that I have ever replaced was physically damaged by reason
>>> of losing a battle with a very large hammer. I had an '89 Ford motorhome
>>> (motorhome on a Ford chassis) that I thought had a CAT problem in about
>>> 2003. The CAT was fine. The muffler was the problem. The muffler was a
>>> significantly less costly repair. The motorhome is still going strong
>>> with the same CAT that I thought needed replacing back in '03.
>>>
>>> I'd not expect any '96 or newer car or truck sold in the USA to have a
>>> CAT problem for several more years.
>>>
>>> The sensors, on the other hand, are not nearly so robust and the
>>> environment they live in is very hostile. I'd suspect a sensor failure
>>> long before a CAT problem.
>>>
>>
>> Pre OBD II vehicles generally did not have a post-cat O2 sensor so there
>> was no on-board way for the vehicle's diagnostic system to evaluate the
>> performance of the cat so you would not get a check engine light related
>> to cat performance. The only way to evaluate cat performance in a
>> pre-OBD II vehicle is with an exhaust gas analyzer (also the best way to
>> evaluate cat performance in an OBD II vehicle).
>>
>> The catalyst in a catalytic converter does not get used up or wear out so
>> it could theoretically last forever. What happens when cats fail is that
>> the catalyst becomes coated with contaminants like particulate (soot) so
>> that the exhaust gas passing over the catalyst bed does not come in
>> contact with the catalyst so no catalytic action occurs, or the converter
>> develops a hole that allows exhaust gas to escape and cool air to enter,
>> or interior corrosion allows the bed holding the catalyst to collapse or
>> come apart, clogging the flow of exhaust.
>>
>> Your motor home probably saw a lot of highway miles, with a nice hot
>> exhaust that minimized buildup of contaminants on the catalyst,
>> prolonging its life.
>> --
>
> 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.

Yup, the effect is like Eddie Murphy sticking a bannana up the tailpipe in
Beverly Hills Cop.

>
> 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.
>

I don't think that cat failure is as rare as you think; it is just that cat
failure is not detected very often, which is why the OBD II standard
included a way to check cat efficiency.
--

Ray O
(correct punctuation to reply)

On Wed, 18 Mar 2009 08:24:21 -0700, "Jeff Strickland"
> wrote:

>
>"Ray O" > wrote in message
...
>>
>> "Jeff Strickland" > wrote in message
>> ...
>>>A catalytic converter is VERY robust, and unless you feed the car leaded
>>>gasoline or some other unauthorized substance, the CAT ought to last the
>>>life of the car.
>>>
>>> The only CAT that I have ever replaced was physically damaged by reason
>>> of losing a battle with a very large hammer. I had an '89 Ford motorhome
>>> (motorhome on a Ford chassis) that I thought had a CAT problem in about
>>> 2003. The CAT was fine. The muffler was the problem. The muffler was a
>>> significantly less costly repair. The motorhome is still going strong
>>> with the same CAT that I thought needed replacing back in '03.
>>>
>>> I'd not expect any '96 or newer car or truck sold in the USA to have a
>>> CAT problem for several more years.
>>>
>>> The sensors, on the other hand, are not nearly so robust and the
>>> environment they live in is very hostile. I'd suspect a sensor failure
>>> long before a CAT problem.
>>>
>>
>> Pre OBD II vehicles generally did not have a post-cat O2 sensor so there
>> was no on-board way for the vehicle's diagnostic system to evaluate the
>> performance of the cat so you would not get a check engine light related
>> to cat performance. The only way to evaluate cat performance in a pre-OBD
>> II vehicle is with an exhaust gas analyzer (also the best way to evaluate
>> cat performance in an OBD II vehicle).
>>
>> The catalyst in a catalytic converter does not get used up or wear out so
>> it could theoretically last forever. What happens when cats fail is that
>> the catalyst becomes coated with contaminants like particulate (soot) so
>> that the exhaust gas passing over the catalyst bed does not come in
>> contact with the catalyst so no catalytic action occurs, or the converter
>> develops a hole that allows exhaust gas to escape and cool air to enter,
>> or interior corrosion allows the bed holding the catalyst to collapse or
>> come apart, clogging the flow of exhaust.
>>
>> Your motor home probably saw a lot of highway miles, with a nice hot
>> exhaust that minimized buildup of contaminants on the catalyst, prolonging
>> its life.
>> --
>
>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.
>
>
>
>
>
>
>
You'd be surprised how marginal many cats are from new - the calaysts
are expensive so as little as possible active material is used.
Anything goes wrong that reduces the effectiveness of the cat AT ALL
and you fail your e-test.

Coolant leak burning antifreeze can poison the cat. The O2 sensor goes
bad, causing the engine to run rich - dead cat. Burning oil? Dead cat.
Leaded gas? dead cat.

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.

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

> wrote in message
...
> 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

What do you want to remove permanently?
--

Ray O
(correct punctuation to reply)