Code P0420-Catalyst Efficiency Below Threshhold Bank 1

K

kaplan3jiim

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?

TIA
Jim
 
Had the same code on my 95 a few years back. Replacing both sensors has s
far solved the problem. Sensors are not easy to get to/remove. Jus
unplugging them is a real PITA
 
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?

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.
NOTE:
Check the following positions.
- Between cylinder head and front exhaust
pipe
- Between front exhaust pipe and front catalytic
converter
- Between front catalytic converter and rear
catalytic converter
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
catalytic converter...

DK
 
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.
NOTE:
Check the following positions.
- Between cylinder head and front exhaust
pipe
- Between front exhaust pipe and front catalytic
converter
- Between front catalytic converter and rear
catalytic converter
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
catalytic converter...

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?

Jim
 
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?


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
believe.

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.
 
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?

Jim

Aftermarket cats are not a direct fit, they need to be welded to your pipes.
Also they typically don't hold up very well. I would encourage you bite the
bullet and get your cat(s) from the dealer.
 
Dave said:
Aftermarket cats are not a direct fit, they need to be welded to your
pipes. Also they typically don't hold up very well. I would encourage
you bite the bullet and get your cat(s) from the dealer.
Hi,
Certain gas brand works better for certain engine.
Here in Canada, I try to avoid Esso brand.
 
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?

TIA
Jim

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.

Dan D
'99 Impreza 2.5 RS
Central NJ USA
 
My son's car has the same code.

I have very same code on my 2000 Mazda Protege ES

having a hard tine figuring out what it is. Mechanics
keeps saying the cat con..... but I'm weary abt that
and suspect O2 sensors
 
I have very same code on my 2000 Mazda Protege ES

having a hard tine figuring out what it is. Mechanics
keeps saying the cat con..... but I'm weary abt that
and suspect O2 sensors

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. ;-)
 
Dano58 said:
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.

Dan D
'99 Impreza 2.5 RS
Central NJ USA
Hi,
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.
 
Dave said:
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.

Ok thanks so much Dave!

I didn't realize al this

Sounds like it is in fact the cat con!
 
So the formal diagnosis is right side has failed and left side is on
the edge. All the bolts upstream are tight as new and no leaks.

OEM replacement cost including $300 labor is quoted as $1700 for the
pair.

Any other options that are worth doing? If I was sure nothing else
major (like engine or transmission) would crop up in the next 2-3
years it would be a worthwhile investment I suppose but has anyone had
any experience with aftermarket or rebuilt ones - which the shop is
trying to price as I write this?

TIA

Jim
 
So the formal diagnosis is right side has failed and left side is on
the edge. All the bolts upstream are tight as new and no leaks.

Is it the cat con?

Or O2 sensors?
 
Is it the cat con?

Or O2 sensors?

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?
 
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?

Unfortunately, yes. They are about 500 buck a pop if you get a good deal.
They aren't difficult to install; much like a muffler. But the beasts are
expensive.
 
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 converters? 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?

Carl
 
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'......

;^)

Carl
 
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?

Ouch!

Damn them things are pricey!
 
How many miles on the converters? 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?

Carl

Carl..
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.

Jim
 

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