I got a second opinion from another mechanic and he suggested
replacing the upstream sensor. But how can an upstream sensor throw an
error about a downstream component (i.e. cat)? Weird. Funny how you
can spend $250 to replace a sensor, and still don't know for sure if
it's going to fix the check engine light on.

Hi,

A couple of thoughts after "interesting" experiences getting past
California smog tests:

Cats do go bad, but it's far more likely you've got an O2 sensor
failure. Not sure how many sensors you have, but it sounds like you have
one in the exhaust stream of the cat. My smog guy tells me this one
rarely goes out (if it's throwing a code, it's obviously working), but
can tell you one of two things:

First is the cat's dead. Think big bucks as you've heard. He says
"emissions wise" the cheap replacements do as well as OEM. HOWEVER, I've
seen nothing but grief down the road w/ OEMs, both on my cars and
others. It starts w/ the installation problems: they usually don't just
bolt in like OEM. From there you could have heating problems--the guys
I've seen put 'em in weren't always the brightest when it came to
figuring out WHY the factory spent all that money for heat shielding! I
was lucky--my carpet only got "warm." An acquaintance wasn't quite so
lucky--he burnt the carpet in his truck pretty badly. So... if you don't
care about driving the car much in the future, go "cheap" but if you
want to return the car to "constant" service, suck it up and buy OEM.
Doing so saved me money in the long run.

The other thing a cat code could mean is the upstream O2 sensor(s) is a
goner. The mixture going to the cat is too rich for it to handle
properly. Nothing wrong w/ the cat itself, it's just overloaded
(especially problematic as the systems age.) Not such big bucks to fix.

My current smog guy says the upstream O2 sensors are generally good for
about 60k miles (though some last longer, none I've had made it past
100k), and cats for about 150k. So you're due for O2 sensors "again"
according to him, but still have another 30k on your cat. Generally!

Were this my car, I'd start by replacing O2 sensors, resetting all
codes, and starting over.

Now, for "urban legend" and such: the entire emissions system HAS to be
up to operating temps to work right. Again, as the car ages, this
becomes more important. One of my smog guys always told me to drive the
car 5-10 miles to get things hot. Another always blocked the throttle
for a full minute to two minutes to make sure the cat in particular was
"hot." My current guy says both approaches should be combined.

He also suggests any time you're "not quite sure" to have a "pre-test"
done. This gives all the readings w/o upsetting the DMV computer w/ a
"failure" reading that stays on the vehicle record (ever do a CarFax
inquiry and see the "failures" on some cars?) He charges me half the
regular price of a test for the pre-test, and applies the charge to the
real test if I'm ok. In other words, if I fail, I pay half price, go fix
whatever it takes, then come back and try again. If it passes the
pre-test, he'll run it again "for real" and only charge me the one full
fee.

You might ask your guy about doing this since you've already had
problems.

Good luck!

Rick

My '02 Impreza Outback got 121,000 miles, and my local subaru dealer
has got a Cat converter check engine code reading.t. They quoted me
$850 to replace the Cat ($650 part + $200 labor).

All I need is to pass the California smogs. I am not driving the car
much anymore anyway (gas prices), just keep it in the driveway for an
occasional camping trip (still cheaper than renting... provided no
major repair costs) so giving out $800 just to register the thing just
does not sound right.

Goggling produced a $150 (???) "Catco" converter. Does anyone have
experience with this beast? Can I bolt it on myself to keep the
smoggers happy?

Also, I am not sure if the sensor in the car gives a yes/no kind of
answer, or actually produces a real number. Meaning that if I knew
that the reading was on the borderline, can I make the car barely pass
somehow (heard some urban legends on driving on a highway before the
test).