There is no direct way for the OBDII to measure cat performance other
than comparing the upstream and downstream sensor values with ideal
numbers in memory.(basically) So, for most cars, it would be like trying
to measure one old component using 2 other old components. But a GOOD
shop should be able to perform tests on the sensors that would show slow
switching or a failed heater circuit, etc. They should also be able to
do a tailpipe emissions test. Basically, your dealer is either corrupt
or incompetent (hard to see a 3rd option here).

This not say its impossible to have more than one bad component. Or,
indeed, replace one now, and need a second component replaced in a few
days/weeks w'ever.

try reading a couple of articles here;
http://www.troublecodes.net/articles/

OBDII..simply explained
Cat. Eff. Failures

Carl

On Jul 2, 1:53 am, runcyclexc...@gmail.com wrote:

Hi all,

I bugged you guys ~2 months ago about a cat converter error code on a
'02 Impreza, and I got some very good suggestions from you.

The problem was an check engine light on (code P0420 - "cat converter
below thershold efficiency"), and my dealer was trying to convince me
to spend $800 on a new CAT. I can't pass the CA smog test with the
test engine light on.

Well, my registration is due in 2 weeks and I just took the car for a
smog test (the dealer protested, saying why bother - well, since the
retests are free, why not).

It passed the smog test ***easily***. At idle the numbers were:
14.6% CO2, 0.1% O2, 17 ppm HC, 0.03% CO, not anywhere close to the max
allowed numbers.

So I runs back to the dealer and ask them just to replace the front O2
sensor. But they *insist* on replacing the cat converter, saying that
if the system says it fails, it fails.

So the question is - how can the cat converter be faulty if the
emissions are fine? Or do the emission people and the cat converter
sensor measure different things?

I can insist on replacing just the O2 sensor ($250 as opposed to $800)
though, but at this point I don't know if I can trust them at all -
unless I misunderstand something.

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).