cat converter, emissions test

[runcyclexcski]

The car is an '02 Impreza, 154K. Runs fine, I just need to pass the VA
emissions test, and I juts got the CEL on. The upstream sensor has
been replaced 1 year ago. A local chain mechanic has charged me $95
for a "diagnosis" and said it's the cat converter (did not give me the
code) for which he wants $1,300. He says the cat is $1,000 (I
specifically asked for an OEM - still $1,000), plus he wants to
replace the downstream sensor, saying that he won't be able to pull
the sensor out w/o breaking it. I have asked if he can first measure
the O2 , NO, and VOCs coming out of the pipe to see if the emissions
are indeed bad - which he refuses to do, saying that the only way the
emissions can pass is when the readout is done from my car's computer,
i.e. I must clear the code before the emissions are clear.

- If it's indeed the converter, can I get away with a cheap $300
converter I keep finding online? All I need is to pass the emissions.
If my 2 sensors are happy with a delta-voltage across a non-brand
converter, I am fine with that.
- Is it worth at this point to buy a computer reader at AutoAnything
and systematically diagnose the problem myself, rather than paying
$95.00 per "diagnosis"? I should be capable to interpret voltages from
the O2 sensors and compare them to the sensors' specs.
- Don't they stick a probe down the pipe anymore to run the emissions
test? What's up with checking the emissions through my own car's
computer - what's the tester's role then?
Thank you all in advance!

 

[S]

Hi Runcyclexcski!

The car is an '02 Impreza, 154K.
Thank you all in advance!

I can't imagine how you would conduct an emissions test w/o an
exhaust probe, but most places that require an emissions test will
automatically fail a car with a CEL lit. And having your own ODB-II
reader is always a good thing; if nothing else, it will allow you to
clear the CEL. Check out the Elmscan products on-line.
Aftermarket CATs are frequently better than the OEM parts they
replace, but the Subaru CAT(s) is/ are, IIRC, in the "Y" pipe, which
complicates things. And after 150K miles, removing an O2 sensor can be
challenging.
What you might do is hit a salvage yard. Technically, they aren't
supposed to re-sell emissions components, but if you ask for a "Y
pipe", rather than a "catalytic converter" you might bypass this
silly-assed regulation.
Good luck!
ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[runcyclexcski]

 I can't imagine how you would conduct an emissions test w/o an
exhaust probe, but most places that require an emissions test will
automatically fail a car with a CEL lit. And having your own ODB-II
reader is always a good thing; if nothing else, it will allow you to
clear the CEL. Check out the Elmscan products on-line.
Aftermarket CATs are frequently better than the OEM parts they
replace, but the Subaru CAT(s) is/ are, IIRC, in the "Y" pipe, which
complicates things. And after 150K miles, removing an O2 sensor can be
challenging.
What you might do is hit a salvage yard. Technically, they aren't
supposed to re-sell emissions components, but if you ask for a "Y
pipe", rather than a "catalytic converter" you might bypass this
silly-assed regulation.
Good luck!
ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

So the code was the old good P0420.
Is there a chance that this is one of the sensors? Can I read the
voltages from the sensors directly , i.e. can I get the raw data from
the computer, instead of relying on cryptic codes? After all, it's
just voltages.
If I must go the cat replacement way, can I replace only one of the
converters with an OEM (from what I understand the Impreza has 2)? I
am driving this car at most for 2 more years, don't want to give away
1,300.

 

[S]

Hi again RCX!

So the code was the old good P0420.
Is there a chance that this is one of the sensors? Can I read the
voltages from the sensors directly , i.e. can I get the raw data from
the computer, instead of relying on cryptic codes? After all, it's
just voltages.
If I must go the cat replacement way, can I replace only one of the
converters with an OEM (from what I understand the Impreza has 2)? I
am driving this car at most for 2 more years, don't want to give away
1,300.

Well, it _could_ simply be a glitch. Could also be the O2 sensor, or
an intermittent in the sensor wiring.
I'd try clearing the code and see how persistent the CEL is before
getting too excited about it.
And while you can certainly measure the O2 sensor output with a DVM,
you will find it challenging with the car idling in the driveway, much
more so while driving. A decent OBD tool will let you monitor these
parameters (and many more) in real time as you tool along. The better
ones will log the data for post analysis, which can be very handy.
The Elmscan unit plugs into a USB port on a laptop. It comes with
basic software, and much more is available as commercial software,
shareware, and freeware. I'm sure there are other good packages out
there, but I have used the Elmscan stuff with good results for several
years, and so can heartily recommend it.
www.ScanTool.net
I know the first CAT on the Impreza (on any Soobie I've ever looked at
FWIW) is in the Y pipe, right where the headers come together. I think
the second one is as well, but it might be in the pipe between the Y
and the muffler; you'll have to look. In any event, the code is
pointing to the first one, the one in the Y. The one time I had to
deal with this, I simply tossed a used Y pipe at it. The O2 sensor (at
least the first one) is also in the Y pipe, so if you get a "known
good" one, you kill two birds with one stone. I just don't know about
aftermarket CATs for this application; presumably they are available.
Feel free to contact me directly if you want more info on the scanner.
ByeBye! S.

Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

 

[clare]

Hi again RCX!



Well, it _could_ simply be a glitch. Could also be the O2 sensor, or
an intermittent in the sensor wiring.

Could also be ethanol gasoline.
Reset the code and fill up with Shell Ultra. Shell has been on record
- at least in Canada- saying there will NEVER be ethanol in Shell
Ultra.

I've had the issue with a Mazda Miata, and switching to Ultra solved
the problem. Put regular in and the CEL comes back on within 2 tanks.

 

[Dave__67]

The car is an '02 Impreza, 154K. Runs fine, I just need to pass the VA
emissions test, and I juts got the CEL on. The upstream sensor has
been replaced 1 year ago. A local chain mechanic has charged me $95
for a "diagnosis" and said it's the cat converter (did not give me the
code) for which he wants $1,300. He says the cat is $1,000 (I
specifically asked for an OEM - still $1,000), plus he wants to
replace the downstream sensor, saying that he won't be able to pull
the sensor out w/o breaking it. I have asked if he can first measure
the O2 , NO, and VOCs coming out of the pipe to see if the emissions
are indeed bad -  which he refuses to do, saying that the only way the
emissions can pass is when the readout is done from my car's computer,
i.e. I must clear the code before the emissions are clear.

- If it's indeed the converter, can I get away with a cheap $300
converter I keep finding online? All I need is to pass the emissions.
If my 2 sensors are happy with a delta-voltage across a non-brand
converter, I am fine with that.
- Is it worth at this point to buy a computer reader at AutoAnything
and systematically diagnose the problem myself, rather than paying
$95.00 per "diagnosis"? I should be capable to interpret voltages from
the O2 sensors and compare them to the sensors' specs.
- Don't they stick a probe down the pipe anymore to run the emissions
test? What's up with checking the emissions through my own car's
computer - what's the tester's role then?
Thank you all in advance!

Whatever you do, don't drill out a sparkplug anti-fouler and put it
between the 2nd O2 sensor and its mounting bung.

This would make the computer happy for about 6 bucks but would be in
violation of town, county, state, federal, solar, and galactic law,
and would poison the world (assuming the cat is actually bad and the
code is not spurious).


Dave

 

[John Varela]

- Don't they stick a probe down the pipe anymore to run the emissions
test? What's up with checking the emissions through my own car's
computer - what's the tester's role then?

Here in Northern Virginia they skip the dyno test for AWD cars
because the test station dynamometers can't handle AWD. I haven't
taken my wife's Forester for emissions testing recently, but I think
they do run an idle emissions test on it.

 

[Dano58]

If it were me, I would -
1) clear the code and see if it reappears. You need to drive at least
100 miles without the CEL before it will disappear from the
computer's memory.
2) If 1 doesn't work, I'd replace that other O2 sensor and see what
happens.
3) If neither 1 nor 2 work, I'd definitely go the 'used y-pipe' route
as suggested.
4) If no luck on 3, I would locate a different shop. $95 is way too
much for a 'computer diagnosis' (BTW, Autozone will pull the codes
for free). Call around and get a few estimates. Even try the dealer.

Dan D
'99 Impreza 2.5 RS (son's)
Central NJ USA

 

[chitown]

Here in Northern Virginia they skip the dyno test for AWD cars
because the test station dynamometers can't handle AWD. I haven't
taken my wife's Forester for emissions testing recently, but I think
they do run an idle emissions test on it.

Apparently this all depends on the state.

In IL, I've never had a tailpipe test. If they plug in a code scanner
and all's clear, you pass. If you have a CEL (or have teh uncleared
long term statuses that won't be clear if you clear the codes just
before the test), you fail.

 

[shorty]

Whatever you do, don't drill out a sparkplug anti-fouler and put it
between the 2nd O2 sensor and its mounting bung.

Just out of curiosity... what in the fratz is a sparkplug anti-fouler?

-rick-

 

[StephenH]

Just out of curiosity... what in the fratz is a sparkplug anti-fouler?

-rick-

its a spacer designed for the spark plugs to lift it up some and
prevent fouling. they drill them out and put them between the o2
sensor so it reads sluggish, and fools the computer that the cat is
doing its job

 

[Dave__67]

its a spacer designed for the spark plugs to lift it up some and
prevent fouling. they drill them out and put them between the o2
sensor so it reads sluggish, and fools the computer that the cat is
doing its job

Way I understand it is the O2 sensors sees less O2 when out of the
exhaust stream, which is the condition it is 'looking for' to confirm
converter operation.

Many a sad bloke has replaced both sensors and the cat only to have
the code return.

Dave

 

[John Varela]

Apparently this all depends on the state.

In IL, I've never had a tailpipe test. If they plug in a code scanner
and all's clear, you pass. If you have a CEL (or have teh uncleared
long term statuses that won't be clear if you clear the codes just
before the test), you fail.

Notice I said "Northern" Virginia. We're in the DC suburbs and
special rules apply here that don't apply to the rest of the state.
(Well, maybe Norfolk or someplace also has enough air pollution to
earn special rules; I wouldn't know.) The Chicago area may have
enough pollution to merit emissions tests that aren't required
elsewhere in Illinois.

 

[clare]

Way I understand it is the O2 sensors sees less O2 when out of the
exhaust stream, which is the condition it is 'looking for' to confirm
converter operation.

Many a sad bloke has replaced both sensors and the cat only to have
the code return.

Dave

Has the OP tried running ethanol-free gasoline yet as I suggested
last week?????
Definitely worth a try , for diagnostic purposes if nothing else.

I've had it happen on Mazdas and Hondas - so nothing saying it can't
be the problem on a Soob.

Try Shell Ultra - it has no ethanol in Canada and I suspect that is
also true in the USA. (they put 10% in regular, none in premium, so
averaged 5% on mid grade.)

 

[runcyclexcski]

 Has the OP tried running ethanol-free gasoline yet as I suggested
last week?????
Definitely worth a try , for diagnostic purposes if nothing else.

I've had it happen on Mazdas and Hondas - so nothing saying it can't
be the problem on a Soob.

Try Shell Ultra - it has no ethanol in Canada and I suspect that is
also true in the USA. (they put 10% in regular, none in premium, so
averaged 5% on mid grade.)

Thank you guys for all the great responses. I will get a computer to
clear the code, drive for 100 miles, and see what happens.Tthen I will
replace the sensor, then I will replace the Y-pipe, etc.

A colleague of mine has suggested that what triggered a CEL could've
been a single instantaneous, no-reproducible, event, not achievable
under everyday conditions. Coincidentally, when the CEL light came up
I was driving on a rough dirt road in WV.The old engine probably was
struggling on a random rough uphill and triggered the emissions above
the allowed threshold for a few seconds. In that case, the on-board
chip will keep that event in the memory as a faulty event, even though
it hasn't happened after that instance.

If CELs are indeed designed to go off this way it's quite
disappointing. Hence my interest in getting a computer to get the raw
data, not a silly binary event (CEL off -> CEL on) that costs $1,300
to take care of. Sounds like a set-up to get the consumer pay $$$ for
a minor problem. I will start working on it tomorrow.

 

[chitown]

Notice I said "Northern" Virginia. We're in the DC suburbs and
special rules apply here that don't apply to the rest of the state.
(Well, maybe Norfolk or someplace also has enough air pollution to
earn special rules; I wouldn't know.) The Chicago area may have
enough pollution to merit emissions tests that aren't required
elsewhere in Illinois.

I'm reporting experience from Chicagoland.

Not sure if anyone ever has a dyno test here but I've ben here a long
time and it's never involved any tailpipe probes or much else other than
a plug in to the odbii port.


To the OP -- I had a p0420 catalytic converter efficiency code off and
on for a long long time. I recently had a code come up about the knock
sensor. Replaced the knock sensor (which is trivially easy to do
yourself btw) and haven't seen any code for 3 weeks now.