more questions about CAT+O2 sensor

Hi, all
I got a lot of kind responses after I posted my original questions
regarding to CAT+O2 sensor. I feel such relief after reading your
responses. So far, the engine check light is still off and I am anxious
to see what will happen next. I have some more questions after reading
your responses:
1. Is it possible that I pumped some "bad" gas that caused the whole
problem? I keep pumping the cheapest gas I can find and never stick to
the brand
2. How could dealer's mechanic tell the internal worn of CAT? Can such
internal worn be detected virtually without taking down the CAT?
3. I am thinking about purchasing an OBD II scanner. If check engine
light is not on, Can I still use it to do some kind of early detection
of my car, e.g., whether the car will pass emission test, etc?

Thanks.

<wenmang@yahoo.com> wrote in message
news:1128691813.727634.218250@g14g2000cwa.googlegroups.com...[color=blue]
> Hi, all
> I got a lot of kind responses after I posted my original questions
> regarding to CAT+O2 sensor. I feel such relief after reading your
> responses. So far, the engine check light is still off and I am anxious
> to see what will happen next. I have some more questions after reading
> your responses:
> 1. Is it possible that I pumped some "bad" gas that caused the whole
> problem? I keep pumping the cheapest gas I can find and never stick to
> the brand[/color]

Possible, but unlikely.
[color=blue]
> 2. How could dealer's mechanic tell the internal worn of CAT? Can such
> internal worn be detected virtually without taking down the CAT?[/color]

They can measure the exhaust gas downstream from the converter. If it isn't
meeting specs, the converter would be considered bad. Most likely, they were
just looking for the quick and profitable fix (replace everything related to
the code, fix the problem, and make lots of money).
[color=blue]
> 3. I am thinking about purchasing an OBD II scanner. If check engine
> light is not on, Can I still use it to do some kind of early detection
> of my car, e.g., whether the car will pass emission test, etc?[/color]

You should be confident if the check engine light is not on, you will pas
the emissions test. That is why the O2 sensor after the converter is there.
It is nice to have a code reader, so you can diagnosis your own problems.

Ed