Got the subject code for check engine light pulled at Auto Zone.
Car is a '97 Subaru with 165,000 miles.
Could this be the catalytic converter? Auto Zone person said it could
be 0xygen sensor. How does on ascertain what the actual problem is?
Is the O2 sensor easily accessible on the 2.2l engine?
In article , email@example.com
The Subaru procedure step by step:
1. Check if there are other codes (P0130, P0133, P0136,P0139, P0037,
P0301,P0302, P0303, P0304,P1130, P1131, P0031,P0032 and P0038?
If yes, investigate those and disregard P0420. If not:
2. Check exhaust system
Check for gas leaks or air suction caused by
loose or dislocated nuts and bolts, and open
hole at exhaust pipes.
Check the following positions.
- Between cylinder head and front exhaust
- Between front exhaust pipe and front catalytic
- Between front catalytic converter and rear
If no problems:
3. CHECK REAR CATALYTIC CONVERTER.
Separate rear catalytic converter from rear
exhaust pipe. Any damage? If not:
4. CHECK FRONT CATALYTIC CONVERTER.
Remove front catalytic converter.
Any damage? If not:
5. Contact Subaru distributor :-)
So unless you have issue elsewhere, things point to a
On Mon, 23 Jun 2008 23:20:53 GMT, firstname.lastname@example.org (DK)
Thanks. Will probably put this on hold unil closer to next June when
emissions inspection is due again. I seem to recall catalytic
converters are quite expensive but one online site has each of them
for under $200. Does that not include the platinum stuff?
Amazingly, last week I got this same code on my 01 2.5L.
My cat is new as of about 10 months ago. O2 sensor is new too, I
I reset the code with my odb-ii scanner, and drove 600 miles and it
hasn't returned. I'm holding my breath and hoping at least.
2001 Legacy Outback Wagon, 2.5L H-4
Chicago, Illinois USA
My son's car has the same code. I did a little research via Google and
am going to replace the O2 sensors - they seem to be the culprit at
least 50% of the time, according to what I've read on-line. Typically,
when a cat 'goes', it breaks up inside and you would get (at least)
some rattling and (at worst) a degredation in performance and/or gas
mileage as the loose material blocks the flow through the cat. My
son's car has neither symptom.
'99 Impreza 2.5 RS
Central NJ USA
The PO420 code sets when the correlation between the front and rear O2
sensors indicates the cat isn't doing it's job. If one of those two O2
sensors were actually bad instead, it would set a completely different code
and not the PO420 code.
If your car has more than 120k miles, it wouldn't hurt to replace the O2
sensors. You're going to need them sooner than later anyway. But after
clearing the codes you can bet the PO420 code will soon return leading you
to replace the cat(s) too.
And yes, I am a mechanic. Not just playing one on the internet. ;-)
Some OBD II scan software can anlyze O2 sensor performance reading the
output voltage. Around 2000, there was bad batch of O2 sensors covered
by warranty. Believe there is a TSB for this. My kids' 2000 Impreza O2
sensors were replaced during scheduled visit to dealer.
No its the cat con(s). O2 sensors are good.
Was first quoted $1400 plus, for parts, for OEM replacement, but now
after checking around it's half that. Still a bit more than a grand
installed. Does that sound reasonable?
How many miles on the O2 sensors? Has someone 'scoped' them to see if
they are slow switching? (lazy) Has anyone done a flow test through the
cat con using the O2 bung? Or even done a sniffer test?
I dunno, I've just read of so many people replacing old sensors to get
cat con codes to go away - of course, if your sensors are not old and/or
you've ever had blown headgaskets or operated the car in a 'rich'
condition - then most likely the converter IS bad. I hope whatever shop
is doing the work has done good troubleshooting. If the code comes back
in a coupla weeks and they want to change the sensor - are they willing
to refund the converter charges? $80 or so is a lot cheaper than $1400
I'm just sayin'......
Thanks for your response.
The CATS are original - 165,000+ miles. Ditto the 02 sensors.
Never blown headgaskets or run the car rich (unless the computer chose
to do so).
Technician did say that one was just above the pass threshhold, which
I assume means he measured something? Not sure if that addresses any
of the suggestions in your first paragraph (not being a technician). I
can run those by him.
Well, 165K is getting elderly for a lot of components - buthat would be
a pretty extreme lifespan for the original sensors I think. many are
getting lazy at 80-120K.
It comes down to this, it would be better to be wrong about the sensors
than wrong about the converter. bya factor of 15-20! personally, I would
want to try changing the front O2 sensor (it is exposed to more heat and
somewhat more corrosive gasses than the rear one) and clear the codes
and wait to see if any return. Start saving your money, and maybe
research discount/online dealer prices for the converter (try
and maybe the local dealership will match
basically, these two sensors are monitoring the gasses entering and
exiting the converter. If readings are outside some limit, they set the
code. There is no 'direct' converter measurement so, if an O2 sensor is
reading incorrectly - it could throw the very same code, erroneously
'blaming' the converter. Kinda like a person going blind and telling
people the lights need replacing! Of course there is a 'heater' circuit
that could also fail in the (front I think?) converter. But that doesn't
seem to tbe the case here.
hey, I'm just some guy that reads a lot on the internet and occasionally
tinkers with cars. If you feel the dealership is being up-front about
everything and has done the proper testing - then you probably should