P0420 comes back after CAT and O2 sensors replaced

In article <E7qdnZIHQYkIF6_YnZ2dnUVZ_r2dnZ2d@ez2.net>,
"Jeff Strickland" <crwlr@yahoo.com> wrote:
[color=blue]
> AND I have faith that the CAT
> is a reliable component,[/color]

Miss placed faith.
The OP has already stated that he did NOT opt for a genuine OEM
Toyota cat.
Fact; original equipment OBD2 certified catalytic convertors have
to by EPA rules, test at better than 75% efficiency.
Aftermarket catalytic convertors only test to 40% efficiency and
often times, a fair amount less.

The problem the OP is having is well known and discussed in the
emissions industry, that being; most aftermarket cats are no
where near efficient enough to meet the OBD2 monitoring criteria,
and in almost all cases, result in a failed repair which is
usually followed by mass parts swapping based on the flawed logic
that the new aftermarket cat -must- be doing its job so there
-must- be another failed component.

[email]wenmang@yahoo.com[/email] wrote:
[color=blue]
> It is raining today, on my way home, the check light turned on and I
> checked, it reads P0420. I just have CAT and 2 O2 sensors(front adn
> back) replaced about a month, how come?[/color]

Before replacing an O2 sensor, I would read their voltages, either
directly or through the car's computer. You'll need either an
oscilloscope (for electronics, not the kind for ignition systems) or a
digital voltage meter (don't use the analog type since it will load
down the sensor too much and slightly damage it). It's best if the
meter has a bar graph because that reacts much faster than the digits
display. The front O2 sensor should read about 1/2 volt AC on the
meter, or about 1 volt peak-peak on the oscilloscope. The rear sensor
should read the same if the catalytic converter doesn't work at all;
otherwise its voltage reading will be much lower, about 0.1V peak-peak.
You may be able to do a very rough check of the catalytic converter by
pointing an infrared thermometer at it. It should be hotter than the
exhaust pipe in front of it by at least tens of degrees.

"Scott in Florida" <askifyouwant@mindspring.net> wrote in message
news:jlb5j29hos0bd16mdv58opsctno8t505cs@4ax.com...[color=blue]
> On Sun, 15 Oct 2006 15:39:07 -0500, "Ray O"
> <rokigawaATtristarassociatesDOTcom> wrote:
>[/color]

<repetitive drivel snipped>
[color=blue]
> I guess the only answer is to get you two a set of gloves...LOL
>
> I have to admit, I'm learning from both of you and grinnin a bit
> along the way....
>[/color]

LOL! You are learning from whoever is right and being confused by whoever
is wrong! <g>

This discussion is a lot like ones my wife and I have with my daughter ;-)
--

Ray O
(correct punctuation to reply)

"aarcuda69062" <nonelson@sbcglobal.net> wrote in message
news:nonelson-BC7A23.17223815102006@newsclstr02.news.prodigy.com...[color=blue]
> In article <E7qdnZIHQYkIF6_YnZ2dnUVZ_r2dnZ2d@ez2.net>,
> "Jeff Strickland" <crwlr@yahoo.com> wrote:
>[color=green]
>> AND I have faith that the CAT
>> is a reliable component,[/color]
>
> Miss placed faith.
> The OP has already stated that he did NOT opt for a genuine OEM
> Toyota cat.
> Fact; original equipment OBD2 certified catalytic convertors have
> to by EPA rules, test at better than 75% efficiency.
> Aftermarket catalytic convertors only test to 40% efficiency and
> often times, a fair amount less.
>
> The problem the OP is having is well known and discussed in the
> emissions industry, that being; most aftermarket cats are no
> where near efficient enough to meet the OBD2 monitoring criteria,
> and in almost all cases, result in a failed repair which is
> usually followed by mass parts swapping based on the flawed logic
> that the new aftermarket cat -must- be doing its job so there
> -must- be another failed component.[/color]


Agreed. My point is that he should never have replaced the CAT in the first
place. He had this code several weeks ago, and my suggestion then was to
replace only the after-CAT sensor. He elected to follow the advice of
another poster and spend more money than I would have spent to replace what
is normally a life item.

If I was getting a P0420 code, I would reset the computer and wait for
another occurance. If it came, then I'd replace the after-CAT sensor and
reset the computer again. If the code repeated at that point, then I'd learn
the troubleshooting procedure for the various sensors and wiring harness.

Now that the CAT has been replaced with an aftermarket part, all bets are
off. I agree that the new CAT might not work well, and if the sensor he
installed required him to splice in a new connector, then I'd suspect that
repair as well. In my humble opinion, he had a relatively easy problem that
has been blown out of proportion. I can't say with any certainty because I
am on the other side of the computer screen, but my gut feeling is that he
had a failed sensor that could have been replaced in less than 5 minutes,
but a different approach was taken. Now, I think he needs professional help
with good parts and diagnostic equipment.

On Sun, 15 Oct 2006 12:25:37 -0700, "Jeff Strickland"
<crwlr@yahoo.com> wrote:[color=blue]
>"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message
>news:cfd71$45328750$180ffe52$18086@msgid.meganewsservers.com...[color=green]
>> "doncee" <nodbcspam9814wanted@charter.net> wrote in message
>> news:Xns985D842964D76medbcSWBEll@216.196.97.131...[/color][/color]
[color=blue][color=green][color=darkred]
>>> Just to add fuel to the bad firmware theory, have a friend who
>>> had this problem on '02 Corolla. Chk light was reset & drove the
>>> vehicle 7 to 10 days to allow the computer recycle then took it
>>> for emission inspection & passed with flying colors. If in fact
>>> the CAT or the mixture being emited was actually bad would not
>>> the vehicle failed emissions??[/color]
>>
>> No, because emissions checks on vehicles with OBD II do not actually
>> sample the emissions. An emissions check on an OBD II vehicle involves
>> plugging a code reader into the OBD II port and reading the contents of
>> the vehicle's computer to make sure that it is ready and has not detected
>> a problem for the past 2 drive cycles. If the vehicle has been driven for
>> 2 drive cycles without detecting an error, then it is "ready," and will
>> pass the emissions check.
>>[color=darkred]
>>> Chk Eng light has come on since
>>> & been reset & stays off for several weeks or months before it
>>> comes on again. Am certainly no expert but this intermitent
>>> behavior certainly sounds like some sort of false\positive &\or
>>> computer problem.
>>> dc[/color]
>>
>> Most diagnostic trouble codes (DTC) have 2-trip detection logic, where the
>> electronic control module (ECM or computer) has to detect a problem on 2
>> consecutive drive cycles, or trips. If the ECM does not detect the
>> problem on 2 consecutive trips, it will turn the malfunction indicator
>> light (MIL or check engine light) off. A marginal problem can make the
>> MIL go on and off.[/color]
>
>I don't know where you live, but in California, they put a probe in the
>exhaust pipe to actually measure the exhaust stream coming out. They do
>other stuff too, but they ALWAYS measure the exhaust output at the tailpipe
>using a probe.[/color]

California does BOTH - first the Testing Computer scans the Car's
ECM Computer and looks for either the AOK code that the engine has
completed two complete drive cycles successfully with no codes set
(which won't be there if the car ECM was reset just before the test in
an attempt to try sneaking by) or for any trouble codes that have been
set.

If it fails that part, there's no sense going any further.

After that step is passed they call for a visual check for tampering
with under hood systems or hacking out cat converters, tampered
evaporative emissions systems, bad gas cap seals, etc.

And only after you pass all that THEN they call for the sniffer
probe to be inserted in the tailpipe and a short drive cycle on a
chassis dynamometer, to see if the ECM's idea of 'Normal' meets with
reality.

--<< Bruce >>--

On Sun, 15 Oct 2006 21:58:45 GMT, Scott in Florida
<askifyouwant@mindspring.net> wrote:[color=blue]
>On Sun, 15 Oct 2006 15:39:07 -0500, "Ray O"
><rokigawaATtristarassociatesDOTcom> wrote:[/color]
[color=blue][color=green]
>>I don't expect everyone to know and understand the answer to question #7, so
>>in my desire to share my experience with and teach those who do not know, I
>>gave the CORRECT answer. My answer happens to agree with the National
>>Institute for Automotive Service Excellence, which is the body that tests
>>and certifies automotive technicians, with the factory serive manual, and I
>>suspect with Haynes, Chilton, and anyone else who actually understands how
>>DTC P0420 is set. Why do you insist in giving advice that is contrary to
>>the advice given by the factory and every legitimate source of automotive
>>information?[/color]
>
>I guess the only answer is to get you two a set of gloves...LOL
>
>I have to admit, I'm learning from both of you and grinnin a bit
>along the way....[/color]

Yeah, Scott - and since Ray seems to be the one who actually knows
WTF he's talking about here, he gets the good gloves. (The ones with
the horseshoes sewn in.) ;-)

Jeff: Stop arguing and talking nonsense and listen to Ray, he has
the training on this stuff. His ASE Certs may have expired, but that
doesn't mean he's suddenly turned into an blithering idiot.

(Several other things could explain that, but I digress...) ;-)

Catalytic converters are reliable, but only to a point - they do
wear out over time and from accumulated use. You are using the old
American Car meme where a car is "worn out and ready to scrap, and buy
a new one at 100,000 miles", and thinking that way yes it's a
"lifetime" item.

And while a catalyst should make it that far, after 100K it's a
crapshoot how much farther. It dies, you replace it and keep going.

And they also get poisoned by lead and other heavy metals that can
get into the system. Coolant leaks, use of the wrong "carburetor"
(throttle body) cleaning solvents or improper sealants that get
through and poison the Platinum and other noble metals in the matrix.

And they can have a partial ceramic matrix meltdown from too much
unburned fuel (bad sparkplug or coil causing a misfire), creating a
bypass passage that lets uncatalyzed hydrocarbons get around the
matrix and out the tailpipe.

When the #2 Oxygen Sensor after the catalyst is making the same wide
voltage swings as the #1 sensor before the catalyst, that's pretty
reliably showing that the catalyst is not working.

If the catalyst is working properly you want to see big and more-or-
less matching swings on both the #1 and #2 Oxygen sensors at a cold
start as soon as the sensors warm up.

And soon after that the catalyst matrix warms up to operating temp
and lights off, and starts burning up the excess hydrocarbons and
pollutants. And while the #1 sensor will keep making bigger swings
with throttle and load changes, you should only see corresponding
*small* voltage swings on the #2 sensor after that. Meaning the
catalyst is scrubbing the gases properly before the #2 sensor.

If the #2 sensor is bad you'll see a very weak or flat-line signal
all the time - cold, hot, full or part throttle, over-run down a hill,
the output will be either a few faint twitches or nothing.

Now you have to determine WHY. Just throwing expensive replacement
parts at the car until the light goes off (and it might never go out)
without understanding /why/ you are doing it is a fool's game.

--<< Bruce >>--

On Sun, 15 Oct 2006 20:24:07 -0500, "Ray O"
<rokigawaATtristarassociatesDOTcom> wrote:
[color=blue]
>
>"Scott in Florida" <askifyouwant@mindspring.net> wrote in message
>news:jlb5j29hos0bd16mdv58opsctno8t505cs@4ax.com...[color=green]
>> On Sun, 15 Oct 2006 15:39:07 -0500, "Ray O"
>> <rokigawaATtristarassociatesDOTcom> wrote:
>>[/color]
>
><repetitive drivel snipped>
>[color=green]
>> I guess the only answer is to get you two a set of gloves...LOL
>>
>> I have to admit, I'm learning from both of you and grinnin a bit
>> along the way....
>>[/color]
>
>LOL! You are learning from whoever is right and being confused by whoever
>is wrong! <g>
>[/color]

LOL....I know who is right, but it is entertaining to watch the
back/forth...

[color=blue]
>This discussion is a lot like ones my wife and I have with my daughter ;-)[/color]

LOL....

Kids are that way....

Some arguments you don't/can't win....


--

Scott in Florida

In article <nPCdnXmZEbiZcK_YnZ2dnUVZ_oidnZ2d@ez2.net>,
"Jeff Strickland" <crwlr@yahoo.com> wrote:
[color=blue][color=green]
> > The problem the OP is having is well known and discussed in the
> > emissions industry, that being; most aftermarket cats are no
> > where near efficient enough to meet the OBD2 monitoring criteria,
> > and in almost all cases, result in a failed repair which is
> > usually followed by mass parts swapping based on the flawed logic
> > that the new aftermarket cat -must- be doing its job so there
> > -must- be another failed component.[/color]
>
>
> Agreed. My point is that he should never have replaced the CAT in the first
> place. He had this code several weeks ago, and my suggestion then was to
> replace only the after-CAT sensor. He elected to follow the advice of
> another poster and spend more money than I would have spent to replace what
> is normally a life item.[/color]

He had diagnostics from two different shops, one a Toyota
dealership that indicated that the cat-con was no longer
functioning.
Catalytic convertors do not last forever, that is why you can buy
replacements. Trick is to buy the -right- replacement.
[color=blue]
> If I was getting a P0420 code, I would reset the computer and wait for
> another occurance. If it came, then I'd replace the after-CAT sensor and
> reset the computer again. If the code repeated at that point, then I'd learn
> the troubleshooting procedure for the various sensors and wiring harness.[/color]

If I had a code P0420, I'd use my scan tool to do some dynamic
testing of the oxygen sensors involved. If I force the fuel
system rich and lean and the oxygen sensors respond accordingly,
then the sensors are functioning as they should be.
[color=blue]
> Now that the CAT has been replaced with an aftermarket part, all bets are
> off. I agree that the new CAT might not work well, and if the sensor he
> installed required him to splice in a new connector, then I'd suspect that
> repair as well.[/color]

I believe that he mentioned in one of his earlier posts that he
bought genuine Toyota sensors on line and saved $40 per sensor
doing so.
[color=blue]
> In my humble opinion, he had a relatively easy problem that
> has been blown out of proportion. I can't say with any certainty because I
> am on the other side of the computer screen, but my gut feeling is that he
> had a failed sensor that could have been replaced in less than 5 minutes,
> but a different approach was taken. Now, I think he needs professional help
> with good parts and diagnostic equipment.[/color]

I think that originally, he got ambiguous advice from the
Firestone store which then planted the seed of doubt when he went
to the dealership. At 150K miles, I wouldn't want to give any
warranty on a job like this when there's a good chance that the
O2 sensors are original or very high mileage, so the
recommendation that both be replaced is sound business management.

There are plenty of trouble codes that will identify a stuck
high, stuck low, lazy, open, or shorted O2 sensor, hell, Nissans
have their share of post cat o2 sensor failures, but they don't
flag a P0420 when it happens.

"Bruce L. Bergman" <blPYTHONbergman@earthlink.invalid> wrote in message
news:go16j2lg07vak2q43lfr336m9jt90mb218@4ax.com...
[color=blue]
> On Sun, 15 Oct 2006 21:58:45 GMT, Scott in Florida
> <askifyouwant@mindspring.net> wrote:[color=green]
>>On Sun, 15 Oct 2006 15:39:07 -0500, "Ray O"
>><rokigawaATtristarassociatesDOTcom> wrote:[/color]
>[color=green][color=darkred]
>>>I don't expect everyone to know and understand the answer to question #7,
>>>so
>>>in my desire to share my experience with and teach those who do not know,
>>>I
>>>gave the CORRECT answer. My answer happens to agree with the National
>>>Institute for Automotive Service Excellence, which is the body that tests
>>>and certifies automotive technicians, with the factory serive manual, and
>>>I
>>>suspect with Haynes, Chilton, and anyone else who actually understands
>>>how
>>>DTC P0420 is set. Why do you insist in giving advice that is contrary to
>>>the advice given by the factory and every legitimate source of automotive
>>>information?[/color]
>>
>>I guess the only answer is to get you two a set of gloves...LOL
>>
>>I have to admit, I'm learning from both of you and grinnin a bit
>>along the way....[/color]
>
> Yeah, Scott - and since Ray seems to be the one who actually knows
> WTF he's talking about here, he gets the good gloves. (The ones with
> the horseshoes sewn in.) ;-)
>
> Jeff: Stop arguing and talking nonsense and listen to Ray, he has
> the training on this stuff. His ASE Certs may have expired, but that
> doesn't mean he's suddenly turned into an blithering idiot.
>
> (Several other things could explain that, but I digress...) ;-)
>
> Catalytic converters are reliable, but only to a point - they do
> wear out over time and from accumulated use. You are using the old
> American Car meme where a car is "worn out and ready to scrap, and buy
> a new one at 100,000 miles", and thinking that way yes it's a
> "lifetime" item.
>
> And while a catalyst should make it that far, after 100K it's a
> crapshoot how much farther. It dies, you replace it and keep going.
>
> And they also get poisoned by lead and other heavy metals that can
> get into the system. Coolant leaks, use of the wrong "carburetor"
> (throttle body) cleaning solvents or improper sealants that get
> through and poison the Platinum and other noble metals in the matrix.
>
> And they can have a partial ceramic matrix meltdown from too much
> unburned fuel (bad sparkplug or coil causing a misfire), creating a
> bypass passage that lets uncatalyzed hydrocarbons get around the
> matrix and out the tailpipe.
>
> When the #2 Oxygen Sensor after the catalyst is making the same wide
> voltage swings as the #1 sensor before the catalyst, that's pretty
> reliably showing that the catalyst is not working.
>
> If the catalyst is working properly you want to see big and more-or-
> less matching swings on both the #1 and #2 Oxygen sensors at a cold
> start as soon as the sensors warm up.
>
> And soon after that the catalyst matrix warms up to operating temp
> and lights off, and starts burning up the excess hydrocarbons and
> pollutants. And while the #1 sensor will keep making bigger swings
> with throttle and load changes, you should only see corresponding
> *small* voltage swings on the #2 sensor after that. Meaning the
> catalyst is scrubbing the gases properly before the #2 sensor.
>
> If the #2 sensor is bad you'll see a very weak or flat-line signal
> all the time - cold, hot, full or part throttle, over-run down a hill,
> the output will be either a few faint twitches or nothing.
>
> Now you have to determine WHY. Just throwing expensive replacement
> parts at the car until the light goes off (and it might never go out)
> without understanding /why/ you are doing it is a fool's game.
>
> --<< Bruce >>--
>[/color]

As usual, an excellent, thorough, and understandable explanation from Bruce!

I generally try not to reply to posts with questions that someone else has
already answered unless I want to correct a wrong answer, provide additional
information, or try to clarify things if there is contradicting information.

I don't mind if people disagree with me on opinions, but like Mr. Spock, I
like using logic and facts as a basis for making recommendations.
--

Ray O
(correct punctuation to reply)

Thanks everybody. I indeed purchased OEM O2 sensors from Toyota
Dealer(online) and both sensors were installed along with aftermarket
CAT. After a week of installation, my car has everything(monitors)
cleared and it passed Pa state inspection. The problem came back after
about 2 weeks of driving since then. The check light is back with P0420
code. The local exhause shop where I had everything installed could not
believe my story and they kept saying that it was almost impossible to
have CAT going bad like that, and they insisted that they hardly saw
CAT defective(1 out of hundreds they installed, maybe). They asked me
to provide the proof by going to Dealer and have it checked. If Dealer
says CAT is bad, they will honor the warranty of CAT. I just cleared
code this weenend, still waiting drive cycle is done. I will send it to
dealer if check light is back, and keep you posted the outcome.


On Oct 16, 11:17 am, aarcuda69062 <nonel...@sbcglobal.net> wrote:[color=blue]
> In article <nPCdnXmZEbiZcK_YnZ2dnUVZ_oidn...@ez2.net>,
> "Jeff Strickland" <c...@yahoo.com> wrote:
>[color=green][color=darkred]
> > > The problem the OP is having is well known and discussed in the
> > > emissions industry, that being; most aftermarket cats are no
> > > where near efficient enough to meet the OBD2 monitoring criteria,
> > > and in almost all cases, result in a failed repair which is
> > > usually followed by mass parts swapping based on the flawed logic
> > > that the new aftermarket cat -must- be doing its job so there
> > > -must- be another failed component.[/color][/color]
>[color=green]
> > Agreed. My point is that he should never have replaced the CAT in the first
> > place. He had this code several weeks ago, and my suggestion then was to
> > replace only the after-CAT sensor. He elected to follow the advice of
> > another poster and spend more money than I would have spent to replace what
> > is normally a life item.He had diagnostics from two different shops, one a Toyota[/color]
> dealership that indicated that the cat-con was no longer
> functioning.
> Catalytic convertors do not last forever, that is why you can buy
> replacements. Trick is to buy the -right- replacement.
>[color=green]
> > If I was getting a P0420 code, I would reset the computer and wait for
> > another occurance. If it came, then I'd replace the after-CAT sensor and
> > reset the computer again. If the code repeated at that point, then I'd learn
> > the troubleshooting procedure for the various sensors and wiring harness.If I had a code P0420, I'd use my scan tool to do some dynamic[/color]
> testing of the oxygen sensors involved. If I force the fuel
> system rich and lean and the oxygen sensors respond accordingly,
> then the sensors are functioning as they should be.
>[color=green]
> > Now that the CAT has been replaced with an aftermarket part, all bets are
> > off. I agree that the new CAT might not work well, and if the sensor he
> > installed required him to splice in a new connector, then I'd suspect that
> > repair as well.I believe that he mentioned in one of his earlier posts that he[/color]
> bought genuine Toyota sensors on line and saved $40 per sensor
> doing so.
>[color=green]
> > In my humble opinion, he had a relatively easy problem that
> > has been blown out of proportion. I can't say with any certainty because I
> > am on the other side of the computer screen, but my gut feeling is that he
> > had a failed sensor that could have been replaced in less than 5 minutes,
> > but a different approach was taken. Now, I think he needs professional help
> > with good parts and diagnostic equipment.I think that originally, he got ambiguous advice from the[/color]
> Firestone store which then planted the seed of doubt when he went
> to the dealership. At 150K miles, I wouldn't want to give any
> warranty on a job like this when there's a good chance that the
> O2 sensors are original or very high mileage, so the
> recommendation that both be replaced is sound business management.
>
> There are plenty of trouble codes that will identify a stuck
> high, stuck low, lazy, open, or shorted O2 sensor, hell, Nissans
> have their share of post cat o2 sensor failures, but they don't
> flag a P0420 when it happens.[/color]

Just came from Toyota Dealer, CAT is found "not operating properly" and
need replacement.
So, I think that the aftermarket CAT is indeed a bad one. The local
exhaust shop was recommended by our local Firestone auto shop and I
paid only $157 for CAT(including the labor, not including the O2
sensors). Now, I am wondering whether the CAT is too cheap to function
properly? what will happen to next one? Local Midas auto shop asked[color=blue]
>$500 for CAT, the local exhaust shop is much cheaper than Midas, not sure that it was a good move for me at first place. I can not decide to ask money back from the exhaust shop and go somewhere else or just go ahead and ask them to install a new one under their warranty? Any adivce?[/color]


On Oct 16, 12:14 pm, "wenm...@yahoo.com" <wenm...@yahoo.com> wrote:[color=blue]
> Thanks everybody. I indeed purchased OEM O2 sensors from Toyota
> Dealer(online) and both sensors were installed along with aftermarket
> CAT. After a week of installation, my car has everything(monitors)
> cleared and it passed Pa state inspection. The problem came back after
> about 2 weeks of driving since then. The check light is back with P0420
> code. The local exhause shop where I had everything installed could not
> believe my story and they kept saying that it was almost impossible to
> have CAT going bad like that, and they insisted that they hardly saw
> CAT defective(1 out of hundreds they installed, maybe). They asked me
> to provide the proof by going to Dealer and have it checked. If Dealer
> says CAT is bad, they will honor the warranty of CAT. I just cleared
> code this weenend, still waiting drive cycle is done. I will send it to
> dealer if check light is back, and keep you posted the outcome.
>
> On Oct 16, 11:17 am, aarcuda69062 <nonel...@sbcglobal.net> wrote:
>
>
>[color=green]
> > In article <nPCdnXmZEbiZcK_YnZ2dnUVZ_oidn...@ez2.net>,
> > "Jeff Strickland" <c...@yahoo.com> wrote:[/color]
>[color=green][color=darkred]
> > > > The problem the OP is having is well known and discussed in the
> > > > emissions industry, that being; most aftermarket cats are no
> > > > where near efficient enough to meet the OBD2 monitoring criteria,
> > > > and in almost all cases, result in a failed repair which is
> > > > usually followed by mass parts swapping based on the flawed logic
> > > > that the new aftermarket cat -must- be doing its job so there
> > > > -must- be another failed component.[/color][/color]
>[color=green][color=darkred]
> > > Agreed. My point is that he should never have replaced the CAT in the first
> > > place. He had this code several weeks ago, and my suggestion then was to
> > > replace only the after-CAT sensor. He elected to follow the advice of
> > > another poster and spend more money than I would have spent to replace what
> > > is normally a life item.He had diagnostics from two different shops, one a Toyota[/color]
> > dealership that indicated that the cat-con was no longer
> > functioning.
> > Catalytic convertors do not last forever, that is why you can buy
> > replacements. Trick is to buy the -right- replacement.[/color]
>[color=green][color=darkred]
> > > If I was getting a P0420 code, I would reset the computer and wait for
> > > another occurance. If it came, then I'd replace the after-CAT sensor and
> > > reset the computer again. If the code repeated at that point, then I'd learn
> > > the troubleshooting procedure for the various sensors and wiring harness.If I had a code P0420, I'd use my scan tool to do some dynamic[/color]
> > testing of the oxygen sensors involved. If I force the fuel
> > system rich and lean and the oxygen sensors respond accordingly,
> > then the sensors are functioning as they should be.[/color]
>[color=green][color=darkred]
> > > Now that the CAT has been replaced with an aftermarket part, all bets are
> > > off. I agree that the new CAT might not work well, and if the sensor he
> > > installed required him to splice in a new connector, then I'd suspect that
> > > repair as well.I believe that he mentioned in one of his earlier posts that he[/color]
> > bought genuine Toyota sensors on line and saved $40 per sensor
> > doing so.[/color]
>[color=green][color=darkred]
> > > In my humble opinion, he had a relatively easy problem that
> > > has been blown out of proportion. I can't say with any certainty because I
> > > am on the other side of the computer screen, but my gut feeling is that he
> > > had a failed sensor that could have been replaced in less than 5 minutes,
> > > but a different approach was taken. Now, I think he needs professional help
> > > with good parts and diagnostic equipment.I think that originally, he got ambiguous advice from the[/color]
> > Firestone store which then planted the seed of doubt when he went
> > to the dealership. At 150K miles, I wouldn't want to give any
> > warranty on a job like this when there's a good chance that the
> > O2 sensors are original or very high mileage, so the
> > recommendation that both be replaced is sound business management.[/color]
>[color=green]
> > There are plenty of trouble codes that will identify a stuck
> > high, stuck low, lazy, open, or shorted O2 sensor, hell, Nissans
> > have their share of post cat o2 sensor failures, but they don't
> > flag a P0420 when it happens.- Hide quoted text -- Show quoted text -[/color][/color]

<wenmang@yahoo.com> wrote in message
news:1161177720.732525.142130@m7g2000cwm.googlegroups.com...[color=blue]
> Just came from Toyota Dealer, CAT is found "not operating properly" and
> need replacement.
> So, I think that the aftermarket CAT is indeed a bad one. The local
> exhaust shop was recommended by our local Firestone auto shop and I
> paid only $157 for CAT(including the labor, not including the O2
> sensors). Now, I am wondering whether the CAT is too cheap to function
> properly? what will happen to next one? Local Midas auto shop asked[color=green]
>>$500 for CAT, the local exhaust shop is much cheaper than Midas, not sure
>>that it was a good move for me at first place. I can not decide to ask
>>money back from the exhaust shop and go somewhere else or just go ahead
>>and ask them to install a new one under their warranty? Any adivce?[/color]
>[/color]

As I've mentioned many times and contrary to what some others incorrectly
think, it is just about impossible to have a false P0420 code due to a bad
O2 sensor #2, so the most likely cause is a bad catalytic converter.

One of the primary "ingredients" in a catalytic converter is platinum, which
is one of the reasons why a catalytic converter is so expensive. The only
way I can think of to get a cat that much cheaper than an OEM one is to use
a lot less platinum. In my opinion, in the case of catalytic converters,
you get what you pay for.

My advice depends on how much longer you intend to keep the car. If you are
only going to keep it for 3 years or less, then go back to the place that
installed it and ask for a replacement under their warranty. If you are
going to keep it for 3 to 5 years, then go to a place like Midas, and if you
are going to keep it longer than that, then get one from a Toyota dealer.
--

Ray O
(correct punctuation to reply)

"Bruce L. Bergman" <blPYTHONbergman@earthlink.invalid> wrote in message
news:90v5j2pa7p6s5hfkrmu73rlc6ql8al9ji1@4ax.com...[color=blue]
> On Sun, 15 Oct 2006 12:25:37 -0700, "Jeff Strickland"
> <crwlr@yahoo.com> wrote:[color=green]
>>"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message
>>news:cfd71$45328750$180ffe52$18086@msgid.meganewsservers.com...[color=darkred]
>>> "doncee" <nodbcspam9814wanted@charter.net> wrote in message
>>> news:Xns985D842964D76medbcSWBEll@216.196.97.131...[/color][/color]
>[color=green][color=darkred]
>>>> Just to add fuel to the bad firmware theory, have a friend who
>>>> had this problem on '02 Corolla. Chk light was reset & drove the
>>>> vehicle 7 to 10 days to allow the computer recycle then took it
>>>> for emission inspection & passed with flying colors. If in fact
>>>> the CAT or the mixture being emited was actually bad would not
>>>> the vehicle failed emissions??
>>>
>>> No, because emissions checks on vehicles with OBD II do not actually
>>> sample the emissions. An emissions check on an OBD II vehicle involves
>>> plugging a code reader into the OBD II port and reading the contents of
>>> the vehicle's computer to make sure that it is ready and has not
>>> detected
>>> a problem for the past 2 drive cycles. If the vehicle has been driven
>>> for
>>> 2 drive cycles without detecting an error, then it is "ready," and will
>>> pass the emissions check.
>>>
>>>> Chk Eng light has come on since
>>>> & been reset & stays off for several weeks or months before it
>>>> comes on again. Am certainly no expert but this intermitent
>>>> behavior certainly sounds like some sort of false\positive &\or
>>>> computer problem.
>>>> dc
>>>
>>> Most diagnostic trouble codes (DTC) have 2-trip detection logic, where
>>> the
>>> electronic control module (ECM or computer) has to detect a problem on 2
>>> consecutive drive cycles, or trips. If the ECM does not detect the
>>> problem on 2 consecutive trips, it will turn the malfunction indicator
>>> light (MIL or check engine light) off. A marginal problem can make the
>>> MIL go on and off.[/color]
>>
>>I don't know where you live, but in California, they put a probe in the
>>exhaust pipe to actually measure the exhaust stream coming out. They do
>>other stuff too, but they ALWAYS measure the exhaust output at the
>>tailpipe
>>using a probe.[/color]
>
> California does BOTH - first the Testing Computer scans the Car's
> ECM Computer and looks for either the AOK code that the engine has
> completed two complete drive cycles successfully with no codes set
> (which won't be there if the car ECM was reset just before the test in
> an attempt to try sneaking by) or for any trouble codes that have been
> set.
>
> If it fails that part, there's no sense going any further.
>
> After that step is passed they call for a visual check for tampering
> with under hood systems or hacking out cat converters, tampered
> evaporative emissions systems, bad gas cap seals, etc.
>
> And only after you pass all that THEN they call for the sniffer
> probe to be inserted in the tailpipe and a short drive cycle on a
> chassis dynamometer, to see if the ECM's idea of 'Normal' meets with
> reality.
>[/color]



Thanks for the clarification, I knew that. I was only responding to what
appeared to be a statement that only codes are scanned. In CA, codes are
scanned and there is the sniff test.