P0420 code and PA state inspection

wrote:
> I have P0420 faulty code issue for over 6 months, and now it is the
> time for PA state inspection. I talked to some guys at Firestone auto
> shop and was told that both O2 sensors need to be replaced along with
> catalytic converter in order to ensure catalytic converter warranty. I
> tried to back-probe the post O2 sensor for my 2000 Corolla with 150K
> miles on it, but failed(Followed the auto repair book, but cannot id
> anything, maybe it is too complicated for me). Firestone asked $100 for
> computer diagnose for the problem and they also said that if post O2
> sensor was bad, they would not know whether catalytic converter was
> good or not because of misleading signal given by post O2 sensor.
> Basically they cannot give positive conclusion on whether post O2 is
> good or not by running computer diagnosis. I have it diagnosed at
> Toyota dealer 6 months ago and when I tried to retrieve diagnose info
> from dealer, what they have is the suggestion to replace both O2 sensor
> and catalytic converter(at that time, I had no idea O2 sensor can cause
> P0420 faulty code) at $1500.
> Here are my questions:
> Is it necessary to replace both O2 sensors for bad catalytic converter?
>
> It seems to me that I run out options but go ahead to have both O2
> sensors and catalytic converter replaced. Any other suggestions for
> what I should do?
>
> Thx

One more ting, is it a good idea to have post O2 sensor replaced first
or both O2 sensors before replacing catalytic converter? I am not sure
whether replacing O2 sensor(s) first is good idea or not, pls advise.
Thx
 >> Stay informed about: P0420 code and PA state inspection 

> It is a common procedure to replace one or both O2 sensors when P0420 comes
> up, however, it is possible to check the signal output from O2 sensors and
> determine whether they are functioning correctly or not, and with an exhaust
> gas analyzer, it is possible to check catalytic converter performance. The
> Toyota dealer should have the equipment to analyze both the O2 sensor signal
> and the exhaust gas.
> --
>
> Ray O
> (correct punctuation to reply)

Thanks very much Ray.
I have it done at dealer 6 months back and when I went back to delaer
this morning and found out what they could tell me is that the
suggestion to replace O2 sensor + catalytic converter. They asked me to
re-do the analysis since over 6-month passed. I don't like to pay the
same service again since it will cost me another $100 and may draw the
same conclusion. Here is what dealer found out at the first time:
"Access ECU, Locate DTC P0420 for catalyst below efficiency
Diagnose catalytic converter internally worn
new catalytic converter and oxygen sensor installed $1530.78 plus tax
Recommendation:
Front motor mount worn $219.55"

They claimed that "catalytic converter internally worn" and I have no
idea how they identify it through exhaust gas analyzer(honestly, I am
not sure whether they run the gas analyzer or not since it only costs
me $56 for checkup)? I am not sure whether I should trust them or not.
I prefer not to spend another $100 to do diagnosis, I may put it into
replacement instead.
Ray, in your opinion, what is the cost effective way to do it?
Thanks.
 >> Stay informed about: P0420 code and PA state inspection 

wrote:
> > It is a common procedure to replace one or both O2 sensors when P0420 comes
> > up, however, it is possible to check the signal output from O2 sensors and
> > determine whether they are functioning correctly or not, and with an exhaust
> > gas analyzer, it is possible to check catalytic converter performance. The
> > Toyota dealer should have the equipment to analyze both the O2 sensor signal
> > and the exhaust gas.
> > --
> >
> > Ray O
> > (correct punctuation to reply)
>
> Thanks very much Ray.
> I have it done at dealer 6 months back and when I went back to delaer
> this morning and found out what they could tell me is that the
> suggestion to replace O2 sensor + catalytic converter. They asked me to
> re-do the analysis since over 6-month passed. I don't like to pay the
> same service again since it will cost me another $100 and may draw the
> same conclusion. Here is what dealer found out at the first time:
> "Access ECU, Locate DTC P0420 for catalyst below efficiency
> Diagnose catalytic converter internally worn
> new catalytic converter and oxygen sensor installed $1530.78 plus tax
> Recommendation:
> Front motor mount worn $219.55"
>
> They claimed that "catalytic converter internally worn" and I have no
> idea how they identify it through exhaust gas analyzer(honestly, I am
> not sure whether they run the gas analyzer or not since it only costs
> me $56 for checkup)? I am not sure whether I should trust them or not.
> I prefer not to spend another $100 to do diagnosis, I may put it into
> replacement instead.
> Ray, in your opinion, what is the cost effective way to do it?
> Thanks.

I just got off phone with dealer rep and he said that they used a
scanner tool to scan the output of O2 sensor and catalytic converter
instead of using exhause gas analyzer. He told me that the scanner does
more than just reading OBDII code and it can pin point the problem. The
conclusion is that the scanner tells them both of post O2 and cat
converter are bad.
 >> Stay informed about: P0420 code and PA state inspection 

Ray O wrote:
> wrote in message
>
> >
> > wrote:
> >> > It is a common procedure to replace one or both O2 sensors when P0420
> >> > comes
> >> > up, however, it is possible to check the signal output from O2 sensors
> >> > and
> >> > determine whether they are functioning correctly or not, and with an
> >> > exhaust
> >> > gas analyzer, it is possible to check catalytic converter performance.
> >> > The
> >> > Toyota dealer should have the equipment to analyze both the O2 sensor
> >> > signal
> >> > and the exhaust gas.
> >> > --
> >> >
> >> > Ray O
> >> > (correct punctuation to reply)
> >>
> >> Thanks very much Ray.
> >> I have it done at dealer 6 months back and when I went back to delaer
> >> this morning and found out what they could tell me is that the
> >> suggestion to replace O2 sensor + catalytic converter. They asked me to
> >> re-do the analysis since over 6-month passed. I don't like to pay the
> >> same service again since it will cost me another $100 and may draw the
> >> same conclusion. Here is what dealer found out at the first time:
> >> "Access ECU, Locate DTC P0420 for catalyst below efficiency
> >> Diagnose catalytic converter internally worn
> >> new catalytic converter and oxygen sensor installed $1530.78 plus tax
> >> Recommendation:
> >> Front motor mount worn $219.55"
> >>
> >> They claimed that "catalytic converter internally worn" and I have no
> >> idea how they identify it through exhaust gas analyzer(honestly, I am
> >> not sure whether they run the gas analyzer or not since it only costs
> >> me $56 for checkup)? I am not sure whether I should trust them or not.
> >> I prefer not to spend another $100 to do diagnosis, I may put it into
> >> replacement instead.
> >> Ray, in your opinion, what is the cost effective way to do it?
> >> Thanks.
> >
> > I just got off phone with dealer rep and he said that they used a
> > scanner tool to scan the output of O2 sensor and catalytic converter
> > instead of using exhause gas analyzer. He told me that the scanner does
> > more than just reading OBDII code and it can pin point the problem. The
> > conclusion is that the scanner tells them both of post O2 and cat
> > converter are bad.
> >
>
> You can go with what they told you and be pretty sure the problem will be
> fixed, or if you are willing to gamble a little, you can go with just the
> Cat and see what other trouble codes, if any come up. The downfall to this
> approach is that you may have to make another trip and pay another
> diagnosis, but the up side is that you won't pay for unnecessary parts.
>
> Here is basically how the O2 sensors and catalytic converter (cat) work:
>
> There is an O2 sensor in the exhaust ahead (upstream, or #1) of the cat, and
> one after the cat (downstream, or #2). Sensor #1 measures oxygen in the
> air, and from that measurement, can determine if the air/fuel mixture has
> too much or too little fuel. Sensor #1 tells the computer what to do, the
> computer makes an adjustment, and then Sensor #1 takes another measurement
> to determine if more adjustment is necessary. This happens very quickly, so
> the signal coming from the O2 sensor is constantly fluctuating.
>
> After the exhaust gas flows past Sensor #1, it enters the cat and gets
> cleaned up, and then flows past Sensor #2. If the cat is working properly,
> the signal from Sensor #2 should not fluctuate. If the signal fluctuates,
> then the computer assumes that the cat is not working and stores trouble
> code P0420.
>
> If sensor #2 were not working, then it wouldn't know the cat is bad or it
> would set a different trouble code.
>
> In other words, the code scanner does not measure the exhaust gas directly;
> it looks at readings from various sensors and infers whether the exhaust is
> clean or not.
> --
>
> Ray O
> (correct punctuation to reply)

Thanks Ray.

After reading your post, I've decided to have the whole things
replaced. In past over 10-months(not 6, sorry), I keep cancelling the
code(P0420). The faulty code used to come up within 2-month. But
recently, it keeps showing up every 2 weeks(no other code except P0420,
pretty consistant). I may assume that post O2 sensor may be good. Local
shop will not provide warranty on Cat unless 2 O2 sensors are replaced
at the same time. Either way, I have to pass PA inspection soon.
Anyway, thanks for the education.
WM
 >> Stay informed about: P0420 code and PA state inspection 

wrote in message

>I have P0420 faulty code issue for over 6 months, and now it is the
> time for PA state inspection. I talked to some guys at Firestone auto
> shop and was told that both O2 sensors need to be replaced along with
> catalytic converter in order to ensure catalytic converter warranty. I
> tried to back-probe the post O2 sensor for my 2000 Corolla with 150K
> miles on it, but failed(Followed the auto repair book, but cannot id
> anything, maybe it is too complicated for me). Firestone asked $100 for
> computer diagnose for the problem and they also said that if post O2
> sensor was bad, they would not know whether catalytic converter was
> good or not because of misleading signal given by post O2 sensor.
> Basically they cannot give positive conclusion on whether post O2 is
> good or not by running computer diagnosis. I have it diagnosed at
> Toyota dealer 6 months ago and when I tried to retrieve diagnose info
> from dealer, what they have is the suggestion to replace both O2 sensor
> and catalytic converter(at that time, I had no idea O2 sensor can cause
> P0420 faulty code) at $1500.
> Here are my questions:
> Is it necessary to replace both O2 sensors for bad catalytic converter?
>
> It seems to me that I run out options but go ahead to have both O2
> sensors and catalytic converter replaced. Any other suggestions for
> what I should do?
>
> Thx
>

It is a common procedure to replace one or both O2 sensors when P0420 comes
up, however, it is possible to check the signal output from O2 sensors and
determine whether they are functioning correctly or not, and with an exhaust
gas analyzer, it is possible to check catalytic converter performance. The
Toyota dealer should have the equipment to analyze both the O2 sensor signal
and the exhaust gas.
--

Ray O
(correct punctuation to reply)
 >> Stay informed about: P0420 code and PA state inspection 

wrote in message

>
>> It is a common procedure to replace one or both O2 sensors when P0420
>> comes
>> up, however, it is possible to check the signal output from O2 sensors
>> and
>> determine whether they are functioning correctly or not, and with an
>> exhaust
>> gas analyzer, it is possible to check catalytic converter performance.
>> The
>> Toyota dealer should have the equipment to analyze both the O2 sensor
>> signal
>> and the exhaust gas.
>> --
>>
>> Ray O
>> (correct punctuation to reply)
>
> Thanks very much Ray.
> I have it done at dealer 6 months back and when I went back to delaer
> this morning and found out what they could tell me is that the
> suggestion to replace O2 sensor + catalytic converter. They asked me to
> re-do the analysis since over 6-month passed. I don't like to pay the
> same service again since it will cost me another $100 and may draw the
> same conclusion. Here is what dealer found out at the first time:
> "Access ECU, Locate DTC P0420 for catalyst below efficiency
> Diagnose catalytic converter internally worn
> new catalytic converter and oxygen sensor installed $1530.78 plus tax
> Recommendation:
> Front motor mount worn $219.55"
>
> They claimed that "catalytic converter internally worn" and I have no
> idea how they identify it through exhaust gas analyzer(honestly, I am
> not sure whether they run the gas analyzer or not since it only costs
> me $56 for checkup)? I am not sure whether I should trust them or not.
> I prefer not to spend another $100 to do diagnosis, I may put it into
> replacement instead.
> Ray, in your opinion, what is the cost effective way to do it?
> Thanks.
>

Most modern service tracking software requires the service advisor to enter
a CCR, or Condition (what the customer is saying or asking), a Cause (what
is causing the condition that the customer is describing, and a Remedy (what
the technician did to fix the problem).

The technician that looked at the car did not write a good explanation of
what he found, and rather than going back to ask the tech, the service
advisor made up the cause. I know this because catalytic converters do not
"wear internally." By definition, a catalyst is something that causes a
chemical change without the catalyst itself changing or being used up, so in
theory, the catalyst in a catalytic converter will last forever. In
reality, the particulates (soot) in the exhaust gradually form a coating on
the catalyst so that the exhaust gas no longer comes in contact with the
catalyst. The other thing that can happen to a catalytic converter is that
the metal structure corrodes and the corrosion blocks the exhaust flow or
coats the catalyst.

My guess is that the both the dealership and Firestone did not actually
check O2 sensor performance and did not do an analysis of the exhaust gas.
They pulled the code and recommended that you change everything that could
cause that code, which is the 2 O2 sensors and the cat itself.

With that shotgun approach, fixing the problem is a pretty sure bet, but
personally, I would prefer to actually check O2 sensor performance before
replacing it. If you are only want to replace one O2 sensor and want to
take a shot at which O2 sensor to replace, replace upstream one in the
exhaust manifold.

If you just want to pass PA emissions, just change the cat. Keep in mind
that after the work is done, it can take up to a week for the computer to
reach "ready" state.
--

Ray O
(correct punctuation to reply)
 >> Stay informed about: P0420 code and PA state inspection 

wrote in message

>
> wrote:
>> > It is a common procedure to replace one or both O2 sensors when P0420
>> > comes
>> > up, however, it is possible to check the signal output from O2 sensors
>> > and
>> > determine whether they are functioning correctly or not, and with an
>> > exhaust
>> > gas analyzer, it is possible to check catalytic converter performance.
>> > The
>> > Toyota dealer should have the equipment to analyze both the O2 sensor
>> > signal
>> > and the exhaust gas.
>> > --
>> >
>> > Ray O
>> > (correct punctuation to reply)
>>
>> Thanks very much Ray.
>> I have it done at dealer 6 months back and when I went back to delaer
>> this morning and found out what they could tell me is that the
>> suggestion to replace O2 sensor + catalytic converter. They asked me to
>> re-do the analysis since over 6-month passed. I don't like to pay the
>> same service again since it will cost me another $100 and may draw the
>> same conclusion. Here is what dealer found out at the first time:
>> "Access ECU, Locate DTC P0420 for catalyst below efficiency
>> Diagnose catalytic converter internally worn
>> new catalytic converter and oxygen sensor installed $1530.78 plus tax
>> Recommendation:
>> Front motor mount worn $219.55"
>>
>> They claimed that "catalytic converter internally worn" and I have no
>> idea how they identify it through exhaust gas analyzer(honestly, I am
>> not sure whether they run the gas analyzer or not since it only costs
>> me $56 for checkup)? I am not sure whether I should trust them or not.
>> I prefer not to spend another $100 to do diagnosis, I may put it into
>> replacement instead.
>> Ray, in your opinion, what is the cost effective way to do it?
>> Thanks.
>
> I just got off phone with dealer rep and he said that they used a
> scanner tool to scan the output of O2 sensor and catalytic converter
> instead of using exhause gas analyzer. He told me that the scanner does
> more than just reading OBDII code and it can pin point the problem. The
> conclusion is that the scanner tells them both of post O2 and cat
> converter are bad.
>

You can go with what they told you and be pretty sure the problem will be
fixed, or if you are willing to gamble a little, you can go with just the
Cat and see what other trouble codes, if any come up. The downfall to this
approach is that you may have to make another trip and pay another
diagnosis, but the up side is that you won't pay for unnecessary parts.

Here is basically how the O2 sensors and catalytic converter (cat) work:

There is an O2 sensor in the exhaust ahead (upstream, or #1) of the cat, and
one after the cat (downstream, or #2). Sensor #1 measures oxygen in the
air, and from that measurement, can determine if the air/fuel mixture has
too much or too little fuel. Sensor #1 tells the computer what to do, the
computer makes an adjustment, and then Sensor #1 takes another measurement
to determine if more adjustment is necessary. This happens very quickly, so
the signal coming from the O2 sensor is constantly fluctuating.

After the exhaust gas flows past Sensor #1, it enters the cat and gets
cleaned up, and then flows past Sensor #2. If the cat is working properly,
the signal from Sensor #2 should not fluctuate. If the signal fluctuates,
then the computer assumes that the cat is not working and stores trouble
code P0420.

If sensor #2 were not working, then it wouldn't know the cat is bad or it
would set a different trouble code.

In other words, the code scanner does not measure the exhaust gas directly;
it looks at readings from various sensors and infers whether the exhaust is
clean or not.
--

Ray O
(correct punctuation to reply)
 >> Stay informed about: P0420 code and PA state inspection 

wrote in message

>
> Ray O wrote:
>> wrote in message
>>
>> >
>> > wrote:
>> >> > It is a common procedure to replace one or both O2 sensors when
>> >> > P0420
>> >> > comes
>> >> > up, however, it is possible to check the signal output from O2
>> >> > sensors
>> >> > and
>> >> > determine whether they are functioning correctly or not, and with an
>> >> > exhaust
>> >> > gas analyzer, it is possible to check catalytic converter
>> >> > performance.
>> >> > The
>> >> > Toyota dealer should have the equipment to analyze both the O2
>> >> > sensor
>> >> > signal
>> >> > and the exhaust gas.
>> >> > --
>> >> >
>> >> > Ray O
>> >> > (correct punctuation to reply)
>> >>
>> >> Thanks very much Ray.
>> >> I have it done at dealer 6 months back and when I went back to delaer
>> >> this morning and found out what they could tell me is that the
>> >> suggestion to replace O2 sensor + catalytic converter. They asked me
>> >> to
>> >> re-do the analysis since over 6-month passed. I don't like to pay the
>> >> same service again since it will cost me another $100 and may draw the
>> >> same conclusion. Here is what dealer found out at the first time:
>> >> "Access ECU, Locate DTC P0420 for catalyst below efficiency
>> >> Diagnose catalytic converter internally worn
>> >> new catalytic converter and oxygen sensor installed $1530.78 plus tax
>> >> Recommendation:
>> >> Front motor mount worn $219.55"
>> >>
>> >> They claimed that "catalytic converter internally worn" and I have no
>> >> idea how they identify it through exhaust gas analyzer(honestly, I am
>> >> not sure whether they run the gas analyzer or not since it only costs
>> >> me $56 for checkup)? I am not sure whether I should trust them or not.
>> >> I prefer not to spend another $100 to do diagnosis, I may put it into
>> >> replacement instead.
>> >> Ray, in your opinion, what is the cost effective way to do it?
>> >> Thanks.
>> >
>> > I just got off phone with dealer rep and he said that they used a
>> > scanner tool to scan the output of O2 sensor and catalytic converter
>> > instead of using exhause gas analyzer. He told me that the scanner does
>> > more than just reading OBDII code and it can pin point the problem. The
>> > conclusion is that the scanner tells them both of post O2 and cat
>> > converter are bad.
>> >
>>
>> You can go with what they told you and be pretty sure the problem will be
>> fixed, or if you are willing to gamble a little, you can go with just the
>> Cat and see what other trouble codes, if any come up. The downfall to
>> this
>> approach is that you may have to make another trip and pay another
>> diagnosis, but the up side is that you won't pay for unnecessary parts.
>>
>> Here is basically how the O2 sensors and catalytic converter (cat) work:
>>
>> There is an O2 sensor in the exhaust ahead (upstream, or #1) of the cat,
>> and
>> one after the cat (downstream, or #2). Sensor #1 measures oxygen in the
>> air, and from that measurement, can determine if the air/fuel mixture has
>> too much or too little fuel. Sensor #1 tells the computer what to do,
>> the
>> computer makes an adjustment, and then Sensor #1 takes another
>> measurement
>> to determine if more adjustment is necessary. This happens very quickly,
>> so
>> the signal coming from the O2 sensor is constantly fluctuating.
>>
>> After the exhaust gas flows past Sensor #1, it enters the cat and gets
>> cleaned up, and then flows past Sensor #2. If the cat is working
>> properly,
>> the signal from Sensor #2 should not fluctuate. If the signal
>> fluctuates,
>> then the computer assumes that the cat is not working and stores trouble
>> code P0420.
>>
>> If sensor #2 were not working, then it wouldn't know the cat is bad or it
>> would set a different trouble code.
>>
>> In other words, the code scanner does not measure the exhaust gas
>> directly;
>> it looks at readings from various sensors and infers whether the exhaust
>> is
>> clean or not.
>> --
>>
>> Ray O
>> (correct punctuation to reply)
>
> Thanks Ray.
>
> After reading your post, I've decided to have the whole things
> replaced. In past over 10-months(not 6, sorry), I keep cancelling the
> code(P0420). The faulty code used to come up within 2-month. But
> recently, it keeps showing up every 2 weeks(no other code except P0420,
> pretty consistant). I may assume that post O2 sensor may be good. Local
> shop will not provide warranty on Cat unless 2 O2 sensors are replaced
> at the same time. Either way, I have to pass PA inspection soon.
> Anyway, thanks for the education.
> WM
>

You're welcome, good luck!
--

Ray O
(correct punctuation to reply)
 >> Stay informed about: P0420 code and PA state inspection 

P0420 -- Catalyst System Efficiency Below Threshold (Bank 1)


I would NOT replace the O2 Sensor(s) or the CAT at this time.

The code says that the stuff coming out of the CAT is not up to snuff, but
the stuff going in is okay. This means the O2 Sensor(s) is(are) okay because
they would throw their own code if they were having a problem. The CAT has
no moving parts, and you are hard pressed anymore to find leaded fuel to put
into the tank -- which is the primary means of destroying a CAT. All you
have left is a false reading from the after-CAT sensor.

Of course, there is an outside chance that the wiring is hosed, but I'd be
inclined to discount that possibility for now. I have a newly acquired '95
Bronco that was throwing a code tied to the O2 Sensors, I replaced the
affected sensor and the code is gone. My point is, the wiring is in good
shape, and my truck is 5 years older than your car.

I'd be at the parts counter requesting the after CAT sniffer before I spent
more than a second or two on other possibilities. Replacing the sensor is an
easy job, it's much like replacing a spark plug. The only difficulty I
foresee is that it might be corroded in place.




wrote in message

>I have P0420 faulty code issue for over 6 months, and now it is the
> time for PA state inspection. I talked to some guys at Firestone auto
> shop and was told that both O2 sensors need to be replaced along with
> catalytic converter in order to ensure catalytic converter warranty. I
> tried to back-probe the post O2 sensor for my 2000 Corolla with 150K
> miles on it, but failed(Followed the auto repair book, but cannot id
> anything, maybe it is too complicated for me). Firestone asked $100 for
> computer diagnose for the problem and they also said that if post O2
> sensor was bad, they would not know whether catalytic converter was
> good or not because of misleading signal given by post O2 sensor.
> Basically they cannot give positive conclusion on whether post O2 is
> good or not by running computer diagnosis. I have it diagnosed at
> Toyota dealer 6 months ago and when I tried to retrieve diagnose info
> from dealer, what they have is the suggestion to replace both O2 sensor
> and catalytic converter(at that time, I had no idea O2 sensor can cause
> P0420 faulty code) at $1500.
> Here are my questions:
> Is it necessary to replace both O2 sensors for bad catalytic converter?
>
> It seems to me that I run out options but go ahead to have both O2
> sensors and catalytic converter replaced. Any other suggestions for
> what I should do?
>
> Thx
>
 >> Stay informed about: P0420 code and PA state inspection 

wrote in message

>
> wrote:
>> I have P0420 faulty code issue for over 6 months, and now it is the
>> time for PA state inspection. I talked to some guys at Firestone auto
>> shop and was told that both O2 sensors need to be replaced along with
>> catalytic converter in order to ensure catalytic converter warranty. I
>> tried to back-probe the post O2 sensor for my 2000 Corolla with 150K
>> miles on it, but failed(Followed the auto repair book, but cannot id
>> anything, maybe it is too complicated for me). Firestone asked $100 for
>> computer diagnose for the problem and they also said that if post O2
>> sensor was bad, they would not know whether catalytic converter was
>> good or not because of misleading signal given by post O2 sensor.
>> Basically they cannot give positive conclusion on whether post O2 is
>> good or not by running computer diagnosis. I have it diagnosed at
>> Toyota dealer 6 months ago and when I tried to retrieve diagnose info
>> from dealer, what they have is the suggestion to replace both O2 sensor
>> and catalytic converter(at that time, I had no idea O2 sensor can cause
>> P0420 faulty code) at $1500.
>> Here are my questions:
>> Is it necessary to replace both O2 sensors for bad catalytic converter?
>>
>> It seems to me that I run out options but go ahead to have both O2
>> sensors and catalytic converter replaced. Any other suggestions for
>> what I should do?
>>
>> Thx
>
> One more ting, is it a good idea to have post O2 sensor replaced first
> or both O2 sensors before replacing catalytic converter? I am not sure
> whether replacing O2 sensor(s) first is good idea or not, pls advise.
> Thx
>


ALWAYS replace the first sensor identified by the diagnostic system before
replacing other sensors or the CAT.

Replace the after-CAT sensor now, and reset the code -- go to Autozone and
buy the sensor, and they will reset the code (turning the light off) for
you, or they will let you use the code reader and reset the codes yourself.
Then, wait for a few days to see if the light comes on again, then use the
code reader again to see what the fault is.

I assume you read the codes, then reset them, then the Check light came on
again. This code (P0420) is one that might come on, then the conditions that
caused it go away on their own but the light remains on for years. I doubt
you are in this situation, but the proof would be to reset the computer
(using the scan tool) and then if the Check light remains out, then you have
no worries. If the light comes on again, AND the new code is also P0420,
then you need the after-CAT sensor.
 >> Stay informed about: P0420 code and PA state inspection 

"Jeff Strickland" wrote in message

>
> wrote in message
>
>>
>> wrote:
>>> I have P0420 faulty code issue for over 6 months, and now it is the
>>> time for PA state inspection. I talked to some guys at Firestone auto
>>> shop and was told that both O2 sensors need to be replaced along with
>>> catalytic converter in order to ensure catalytic converter warranty. I
>>> tried to back-probe the post O2 sensor for my 2000 Corolla with 150K
>>> miles on it, but failed(Followed the auto repair book, but cannot id
>>> anything, maybe it is too complicated for me). Firestone asked $100 for
>>> computer diagnose for the problem and they also said that if post O2
>>> sensor was bad, they would not know whether catalytic converter was
>>> good or not because of misleading signal given by post O2 sensor.
>>> Basically they cannot give positive conclusion on whether post O2 is
>>> good or not by running computer diagnosis. I have it diagnosed at
>>> Toyota dealer 6 months ago and when I tried to retrieve diagnose info
>>> from dealer, what they have is the suggestion to replace both O2 sensor
>>> and catalytic converter(at that time, I had no idea O2 sensor can cause
>>> P0420 faulty code) at $1500.
>>> Here are my questions:
>>> Is it necessary to replace both O2 sensors for bad catalytic converter?
>>>
>>> It seems to me that I run out options but go ahead to have both O2
>>> sensors and catalytic converter replaced. Any other suggestions for
>>> what I should do?
>>>
>>> Thx
>>
>> One more ting, is it a good idea to have post O2 sensor replaced first
>> or both O2 sensors before replacing catalytic converter? I am not sure
>> whether replacing O2 sensor(s) first is good idea or not, pls advise.
>> Thx
>>
>
>
> ALWAYS replace the first sensor identified by the diagnostic system before
> replacing other sensors or the CAT.

Bad advice. One should always CHECK the component identified by the
diagnostic system. In the case of P0420, based on a signal from the sensor,
the ECM determined that the cat is bad. The system cannot really give a
false "cat is bad" code.

Think of the signal from the O2 sensor as an EKG. #1 sensor sniffs oxygen,
sends a signal to the ECM to adjust injector duration, takes another sniff,
and adjusts some more. When it is in closed loop mode, it is continually
varying voltage.

Then, if the cat is working, it cleans the nasties out of the exhaust
stream, and then sensor #2 takes sniffs. If the exhaust is clean, sensor #2
sends a flat line signal because sensor #1 has already done the work of
adjusting the air/fuel ratio. If the cat isn't working, then the signal
from sensor 2 would be the same as the signal from #1 - in other words, it
is working.

If you think about the logic, it is theoretically to get a false 'cat is
good' if sensor 2 were bad but because it takes an active sensor 2 to give a
cat is bad signal, it has to be good.

>
> Replace the after-CAT sensor now, and reset the code -- go to Autozone and
> buy the sensor, and they will reset the code (turning the light off) for
> you, or they will let you use the code reader and reset the codes
> yourself. Then, wait for a few days to see if the light comes on again,
> then use the code reader again to see what the fault is.

I am not a fan of aftermarket O2 sensors because many of them require
snipping and splicing wires, and that splice makes a big weak point in the
circuit.

>
> I assume you read the codes, then reset them, then the Check light came on
> again. This code (P0420) is one that might come on, then the conditions
> that caused it go away on their own but the light remains on for years. I
> doubt you are in this situation, but the proof would be to reset the
> computer (using the scan tool) and then if the Check light remains out,
> then you have no worries. If the light comes on again, AND the new code is
> also P0420, then you need the after-CAT sensor.
>

Again, there is a different code for a bad after-cat sensor.
--

Ray O
(correct punctuation to reply)
 >> Stay informed about: P0420 code and PA state inspection 

Ray O wrote:
> "Jeff Strickland" wrote in message
>
> >
> > wrote in message
> >
> >>
> >> wrote:
> >>> I have P0420 faulty code issue for over 6 months, and now it is the
> >>> time for PA state inspection. I talked to some guys at Firestone auto
> >>> shop and was told that both O2 sensors need to be replaced along with
> >>> catalytic converter in order to ensure catalytic converter warranty. I
> >>> tried to back-probe the post O2 sensor for my 2000 Corolla with 150K
> >>> miles on it, but failed(Followed the auto repair book, but cannot id
> >>> anything, maybe it is too complicated for me). Firestone asked $100 for
> >>> computer diagnose for the problem and they also said that if post O2
> >>> sensor was bad, they would not know whether catalytic converter was
> >>> good or not because of misleading signal given by post O2 sensor.
> >>> Basically they cannot give positive conclusion on whether post O2 is
> >>> good or not by running computer diagnosis. I have it diagnosed at
> >>> Toyota dealer 6 months ago and when I tried to retrieve diagnose info
> >>> from dealer, what they have is the suggestion to replace both O2 sensor
> >>> and catalytic converter(at that time, I had no idea O2 sensor can cause
> >>> P0420 faulty code) at $1500.
> >>> Here are my questions:
> >>> Is it necessary to replace both O2 sensors for bad catalytic converter?
> >>>
> >>> It seems to me that I run out options but go ahead to have both O2
> >>> sensors and catalytic converter replaced. Any other suggestions for
> >>> what I should do?
> >>>
> >>> Thx
> >>
> >> One more ting, is it a good idea to have post O2 sensor replaced first
> >> or both O2 sensors before replacing catalytic converter? I am not sure
> >> whether replacing O2 sensor(s) first is good idea or not, pls advise.
> >> Thx
> >>
> >
> >
> > ALWAYS replace the first sensor identified by the diagnostic system before
> > replacing other sensors or the CAT.
>
> Bad advice. One should always CHECK the component identified by the
> diagnostic system. In the case of P0420, based on a signal from the sensor,
> the ECM determined that the cat is bad. The system cannot really give a
> false "cat is bad" code.
>
> Think of the signal from the O2 sensor as an EKG. #1 sensor sniffs oxygen,
> sends a signal to the ECM to adjust injector duration, takes another sniff,
> and adjusts some more. When it is in closed loop mode, it is continually
> varying voltage.
>
> Then, if the cat is working, it cleans the nasties out of the exhaust
> stream, and then sensor #2 takes sniffs. If the exhaust is clean, sensor #2
> sends a flat line signal because sensor #1 has already done the work of
> adjusting the air/fuel ratio. If the cat isn't working, then the signal
> from sensor 2 would be the same as the signal from #1 - in other words, it
> is working.
>
> If you think about the logic, it is theoretically to get a false 'cat is
> good' if sensor 2 were bad but because it takes an active sensor 2 to give a
> cat is bad signal, it has to be good.
>
> >
> > Replace the after-CAT sensor now, and reset the code -- go to Autozone and
> > buy the sensor, and they will reset the code (turning the light off) for
> > you, or they will let you use the code reader and reset the codes
> > yourself. Then, wait for a few days to see if the light comes on again,
> > then use the code reader again to see what the fault is.
>
> I am not a fan of aftermarket O2 sensors because many of them require
> snipping and splicing wires, and that splice makes a big weak point in the
> circuit.
>
> >
> > I assume you read the codes, then reset them, then the Check light came on
> > again. This code (P0420) is one that might come on, then the conditions
> > that caused it go away on their own but the light remains on for years. I
> > doubt you are in this situation, but the proof would be to reset the
> > computer (using the scan tool) and then if the Check light remains out,
> > then you have no worries. If the light comes on again, AND the new code is
> > also P0420, then you need the after-CAT sensor.
> >
>
> Again, there is a different code for a bad after-cat sensor.
> --
>
> Ray O
> (correct punctuation to reply)

Fortunately, the exhause shop allows me to purchase Toyota O2 sensors
and installs them for me for a $100. I have ordered O2 sensors
online(waiting for shipment now) and each costs me $100 which is much
cheaper compared with the one offered by the shop($140 each).
I tried very hard to rremove psot-O2 sensor, but I could not and it
stucks and I don't have decent equipment to raise the car high enough I
guess to apply full-force.
 >> Stay informed about: P0420 code and PA state inspection 

"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message

>
> "Jeff Strickland" wrote in message
>
>>
>> wrote in message
>>
>>>
>>> wrote:
>>>> I have P0420 faulty code issue for over 6 months, and now it is the
>>>> time for PA state inspection. I talked to some guys at Firestone auto
>>>> shop and was told that both O2 sensors need to be replaced along with
>>>> catalytic converter in order to ensure catalytic converter warranty. I
>>>> tried to back-probe the post O2 sensor for my 2000 Corolla with 150K
>>>> miles on it, but failed(Followed the auto repair book, but cannot id
>>>> anything, maybe it is too complicated for me). Firestone asked $100 for
>>>> computer diagnose for the problem and they also said that if post O2
>>>> sensor was bad, they would not know whether catalytic converter was
>>>> good or not because of misleading signal given by post O2 sensor.
>>>> Basically they cannot give positive conclusion on whether post O2 is
>>>> good or not by running computer diagnosis. I have it diagnosed at
>>>> Toyota dealer 6 months ago and when I tried to retrieve diagnose info
>>>> from dealer, what they have is the suggestion to replace both O2 sensor
>>>> and catalytic converter(at that time, I had no idea O2 sensor can cause
>>>> P0420 faulty code) at $1500.
>>>> Here are my questions:
>>>> Is it necessary to replace both O2 sensors for bad catalytic converter?
>>>>
>>>> It seems to me that I run out options but go ahead to have both O2
>>>> sensors and catalytic converter replaced. Any other suggestions for
>>>> what I should do?
>>>>
>>>> Thx
>>>
>>> One more ting, is it a good idea to have post O2 sensor replaced first
>>> or both O2 sensors before replacing catalytic converter? I am not sure
>>> whether replacing O2 sensor(s) first is good idea or not, pls advise.
>>> Thx
>>>
>>
>>
>> ALWAYS replace the first sensor identified by the diagnostic system
>> before replacing other sensors or the CAT.
>
> Bad advice. One should always CHECK the component identified by the
> diagnostic system. In the case of P0420, based on a signal from the
> sensor, the ECM determined that the cat is bad. The system cannot really
> give a false "cat is bad" code.
>

Agreed, but there is no check for the CAT. The only thing to do is check the
sensor, or simply replace it and cross one's fingers that everything else is
okay, and the sensor is simply not working. sure, one could test the
resistance, but any test done at home will be a static test -- the
conditions are constant, not changing -- and the error is related to a
dynamic set of parameters -- it is looking for changing conditions. I can't
think of a dynamic test that can be done at home, although I readily agree
that theyr COULD be a dynamic test that may be accomplished in the shop --
although I have no knowledge that such a test actually exists.



> Think of the signal from the O2 sensor as an EKG. #1 sensor sniffs
> oxygen, sends a signal to the ECM to adjust injector duration, takes
> another sniff, and adjusts some more. When it is in closed loop mode, it
> is continually varying voltage.
>
> Then, if the cat is working, it cleans the nasties out of the exhaust
> stream, and then sensor #2 takes sniffs. If the exhaust is clean, sensor
> #2 sends a flat line signal because sensor #1 has already done the work of
> adjusting the air/fuel ratio. If the cat isn't working, then the signal
> from sensor 2 would be the same as the signal from #1 - in other words, it
> is working.
>
> If you think about the logic, it is theoretically to get a false 'cat is
> good' if sensor 2 were bad but because it takes an active sensor 2 to give
> a cat is bad signal, it has to be good.
>
>>
>> Replace the after-CAT sensor now, and reset the code -- go to Autozone
>> and buy the sensor, and they will reset the code (turning the light off)
>> for you, or they will let you use the code reader and reset the codes
>> yourself. Then, wait for a few days to see if the light comes on again,
>> then use the code reader again to see what the fault is.
>
> I am not a fan of aftermarket O2 sensors because many of them require
> snipping and splicing wires, and that splice makes a big weak point in the
> circuit.
>
>>
>> I assume you read the codes, then reset them, then the Check light came
>> on again. This code (P0420) is one that might come on, then the
>> conditions that caused it go away on their own but the light remains on
>> for years. I doubt you are in this situation, but the proof would be to
>> reset the computer (using the scan tool) and then if the Check light
>> remains out, then you have no worries. If the light comes on again, AND
>> the new code is also P0420, then you need the after-CAT sensor.
>>
>
> Again, there is a different code for a bad after-cat sensor.


Splitting hairs, Ray. P0420 _IS_ the after-CAT sensor. It is reporting that
what comes out of the CAT is not what the system is looking for, by
definition making it the After CAT Sensor. Anything reported in this range
of codes is saying that either the CAT itself is bad or that the sensor's
internal heating element is not working. Since we do not have a heatrer
element error code, then the CAT is bad OR the sensor itself is bad. My vote
is on the sensor.
 >> Stay informed about: P0420 code and PA state inspection