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<wenmang@yahoo.com> wrote in message
news:1158928402.688874.131500@k70g2000cwa.googlegroups.com...[color=blue]
> Thanks Ray. Every reader in this group may have idea who is expert and
> who always provide sound advices to newbies like myself. The learning
> curve may be too deep for me and I try to ask more stupid questions as
> possible as I can. Please bear with me.
> Sorry I didn't address my question clearly. I have two Corollas. 2000
> Corolla has new CAT and 2 O2 sensors replaced and ready for State
> inspection(due to bad CAT). My other Corolla(2001) had check-light
> on(MIL was set) in July and faulty code is P0420 which is the same one
> that my 2000 Corolla had/repaired for, and I had it cleared in July.
> But since then CAT monitor has been stuck for my 2001 Corolla and about
> 2 months have passed, still the monitor cycle is not done. So, I
> followed your advice and subscribed to Toyota techinfo.com and obtained
> the procedure to run the drive cycle. Now, the CAT monitor is done but
> no faulty code. That is reason why I was asking you why check-light
> went on at the first place in July. If check-light was on and faulty
> code was P0420 in July, now it disappears, what does it mean for the
> same car?
>
>[/color]

OK, now your question makes a lot more sense.

For the 2001 Corolla, I cannot give you a definitive answer as to why DTC
P0420 cleared itself up and has not returned. Because of the 2-trip
detection logic, it is possible that the conditions have not appeared on 2
consecutive drive cycles, or perhaps the catalytic converter was beginning
to become coated with contaminants, and a trip on the highway burned off the
contaminants.

I believe that the trouble code will re-appear within the next 2 or 3
months, and if it does while the vehicle is still covered by the emissions
warranty, do not clear the code. Instead, take it to the dealership for
repair under the emissions warranty.
--

Ray O
(correct punctuation to reply)