<wenmang@yahoo.com> wrote in message
news:1160669044.902786.193420@i3g2000cwc.googlegroups.com...[color=blue]
> The scan tool I mean is the equipment to scan CAT system including O2
> signals not the OBDII reader. I went to the local exhaust shop this
> morning, they were not happy. They claimed that it was impossible for a
> brand new CAT going bad within a month, there must have something wrong
> with my car. They argued that there are a lot of factors which might
> cause P0420 code set by the computer and they asked me to send my car
> to dealer for check up, and they would not honor the warranty unless
> dealer says it is bad(they were not convinced that CAT could be
> defective). I am wondering whether there is other factor(s) that may
> set P0420? I like to cancel the code and wait to see what will happen
> next since it just passed the inspection and I have a year to find out.
> I am wondering whether there may be false alarm for some unknown
> reason. Anyway, it is very frustrated for me having to deal with P0420
> code allover again.[/color]
I personally prefer dealership service departments to avoid the very
predicament you are facing. Toyota requires dealerships to have certain
equipment, among them an exhaust gas analyzer, their technicians are
factory-trained, and the warranty is backed up by the most financially
secure car company in the world.
The logic of how the ECM sets Diagnostic Trouble Code (DTC) P0420 is such
that the most likely cause is a bad catalytic converter. #1 and #2 O2
sensors work the same way and detect the presence of oxygen (O2) in the
exhaust.
Sensor #1 is sniffing the exhaust gas before it passes through the cat, and
with the injectors sending fuel in pulses, the amount of O2 in the exhaust
gas varies, so the voltage signal from Sensor #1 varies up and down.
Sensor #2 sniffs the exhaust gas after it has passed through the cat, and
the cat is supposed to clean up the gas. If the cat is working, the the
voltage signal from sensor #2 should be much more even than the signal from
sensor #1. If the signal from sensor #2 is varying and looks the same as
the signal from sensor #1, then the cat has not changed the exhaust and the
ECM sets DTC P0420.
Other possible causes of P0420 are a damaged exhaust manifold or exhaust
pipe (you would probably hear an exhaust leak), engine coolant temperature
sensor not working properly, retarded spark timing, or bad O2 sensor.
At this point, your best bet is to have a dealership diagnose the condition
and with a written diagnosis, go back to the shop that did the work if
something they replaced is bad.
--
Ray O
(correct punctuation to reply)[color=blue]
>
>
> On Oct 12, 12:39 am, "Ray O" <rokigawaATtristarassociatesDOTcom>
> wrote:[color=green]
>> <wenm...@yahoo.com> wrote in
>> messagenews:1160609005.854927.323010@m7g2000cwm.googlegroups.com...
>>[color=darkred]
>> > Thanks Ray. I live in PA and I don't think that any place in US sells
>> > leaded fuel
>> > and I see no smoke coming out of exhaust pipe. The place where I have
>> > CAT
>> > replaced doesn't have scan tool. So I may have to send my car to other
>> > place for the
>> > scan in order to make sure that O2 sensors are good before exaust shop
>> > can carry
>> > out warranty otherwise, they probably won't do anything.No regular gas
>> > stations sell leaded fuel, and
AFAIK, leaded fuel is not[/color]
>> available in the U.S., but I like to cover all bases when I think of it
>> ;-)
>>
>> No smoke out of the tail pipe is good!
>>
>> If the place that replaced the cat does not have a scan tool, then how
>> did
>> you get the code? If you have a personal scan tool, perhaps the shop
>> that
>> replaced the can use it to check the codes. You can chcek O2 sensor
>> operation with a volt meter.
>>
>> If the cat is aftermarket, I'd bet that the replacement cat is bad.
>>
>> Good luck!
>> --
>>
>> Ray O
>> (correct punctuation to reply)
>>
>>
>>
>>
>>[color=darkred]
>> > On Oct 11, 6:55 pm, "Ray O" <rokigawaATtristarassociatesDOTcom> wrote:
>> >> <wenm...@yahoo.com> wrote in
>> >> messagenews:1160599775.545655.124910@k70g2000cwa.googlegroups.com...[/color]
>>[color=darkred]
>> >> > Hi,[/color]
>>[color=darkred]
>> >> > 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? what possibly went wrong?
>> >> > What
>> >> > should I do next?My guess would be that the replacement catalytic
>> >> > converter is defective or
>> >> something is contaminating the catalyst.[/color]
>>[color=darkred]
>> >> Leaded fuel or huge amounts of engine oil leaking into the combustion
>> >> chamber (with accompanying blue-gray clouds out the exhaust) could
>> >> contaminate the catalyst, but if you don't see the blue-gray smoke and
>> >> you
>> >> haven't used leaded fuel, then a defective catalytic converter is
>> >> likely.[/color]
>>[color=darkred]
>> >> I would bring the car back to the place that installed the cat and
>> >> sensors
>> >> for a warranty repair.[/color]
>>[color=darkred]
>> >> Good luck!
>> >> --[/color]
>>[color=darkred]
>> >> Ray O
>> >> (correct punctuation to reply)- Hide quoted text -- Show quoted text -[/color][/color]
>[/color]
