CEL, dealer says I need new catalytic converters

[Manny]

I have a 99 SOW with 105K miles. This past weekend the CEL came on and
I took it to the dealer. They say they pulled code P0420 (Cat
efficiency below threshold bank 1), and told me I need to "replace
catalytic converters and possibly both sensors and hardware."

I've done some reading on this topic and I have a few questions that I
hope someone could answer. First off, I'm a bit uneasy about the
vageness of the diagnose. It sounds like they're not sure whether it's
a bad cat, a bad sensor, or a bad gasket. I don't want to pay $1200 for
the job if all that's really necessary is an exhaust gasket or a new O2
sensor.

Is it normal that both cats go bad and need replacement at the same
time? How easy and expensive would be to just replace the sensors and
the gaskets as a first step? Does the P0420 code really mean "bad cat,
must replace" or is it just an indication of different readings between
the 2 sensors (which may or may not be due to a bad cat)?

Any suggestions on how I should proceed?

Thanks in advance,

- Manuel.

 

[AS]

Unless your vehicle is burning oil, it is very unlikely that your
catalytic converter is worn out.

Try testing the O2 sensors first.

Was the 0420 code the only one?

Good luck!

 

[Carl 1 Lucky Texan]

I have a 99 SOW with 105K miles. This past weekend the CEL came on and
I took it to the dealer. They say they pulled code P0420 (Cat
efficiency below threshold bank 1), and told me I need to "replace
catalytic converters and possibly both sensors and hardware."

I've done some reading on this topic and I have a few questions that I
hope someone could answer. First off, I'm a bit uneasy about the
vageness of the diagnose. It sounds like they're not sure whether it's
a bad cat, a bad sensor, or a bad gasket. I don't want to pay $1200 for
the job if all that's really necessary is an exhaust gasket or a new O2
sensor.

Is it normal that both cats go bad and need replacement at the same
time? How easy and expensive would be to just replace the sensors and
the gaskets as a first step? Does the P0420 code really mean "bad cat,
must replace" or is it just an indication of different readings between
the 2 sensors (which may or may not be due to a bad cat)?

Any suggestions on how I should proceed?

Thanks in advance,

- Manuel.

I would do this incrementally I think, change front O2 first (it get's
more heat and more contaminants if there is a headgasket leaking.).
Reset the ECU, drive. If the CEL comes back, change the rear sensor.

A good mechanic can test the sensors to see if they are 'lazy'. It IS
possible to need a converter at 105K - just not likely if the car has
had no previous 'issues' and has otherwise been well treated.

Carl

 

[Backfire Bob]

I have a 99 SOW with 105K miles. This past weekend the CEL came on and
I took it to the dealer. They say they pulled code P0420 (Cat
efficiency below threshold bank 1), and told me I need to "replace
catalytic converters and possibly both sensors and hardware."

I've done some reading on this topic and I have a few questions that I
hope someone could answer. First off, I'm a bit uneasy about the
vageness of the diagnose. It sounds like they're not sure whether it's
a bad cat, a bad sensor, or a bad gasket. I don't want to pay $1200 for
the job if all that's really necessary is an exhaust gasket or a new O2
sensor.

Is it normal that both cats go bad and need replacement at the same
time? How easy and expensive would be to just replace the sensors and
the gaskets as a first step? Does the P0420 code really mean "bad cat,
must replace" or is it just an indication of different readings between
the 2 sensors (which may or may not be due to a bad cat)?

Any suggestions on how I should proceed?

Thanks in advance,

- Manuel.

This is SO TYPICAL of Subaru's service/dealers.
Get a second opinion, DO NOT mention to them you have had a quote from
another dealer.
See if they come to the same conclusion (bet they don't).
At 105,000 Miles the O2 sensors probably ARE dead. You can buy the Bosch
replacements from "Autozone"
if you have one nearby. Call around, they vary widely in price.($40 at
Autozone/$65 at Pep Boys)
You can do them yourself, not hard to replace just do it with the car stone
cold.
The O2 (oxygen) sensor(s) is a good place to start.Remember to clear the
codes after you mess with it.
In fact.....I would clear it and see if it comes back again. Some autoparts
stores will pull the codes for you
for FREE. "Autozone" is one of them.

 

[Edward Hayes]

IF AFTER determining that you do need a new cat consider this. Factory
cats are expensive and one reason is that they are designed to exceed
the 80,000 mile minimum government mandate. There are aftermarket cats
available that are much cheaper but, probably won't last as long. So
it depends on how long you wish to keep your vehicle. JMO

 

[Rick Courtright]

the 80,000 mile minimum government mandate. There are aftermarket cats
available that are much cheaper but, probably won't last as long. So

Hi,

I'll attest to the possibility of a short life expectancy of an
aftermarket cat... limped home at 3 mph and VERY hot exhaust system
(didn't damage car, but could have if I'd had to go very far--an
acquaintance burned up the carpet in his vehicle under similar
circumstances) when one self-destructed and blocked the entire exhaust
system. Factory cat is "cheaper" in the long run IME!

Rick

 

[Manny]

You guys have been a great help. Thanks a lot for all the replies.
I will try replacing the forward O2 sensor first and go from there,
assuming I don't see any major visible damage to the cat. I haven't
looked under there yet but I live in New England, so a damaged cat or
exhaust gasket due to corrosion is always a possibility.

One more question. How do I reset the ECU? Do I need to take it back to
the dealer for that or can they do it at AutoZone? Will unplugging the
battery reset the ECU? The dealer did reset the CEL this time an it
hasn't come on in the 50+mi that I have driven so far.

- Manuel.

 

[Mickey]

You guys have been a great help. Thanks a lot for all the replies.
I will try replacing the forward O2 sensor first and go from there,
assuming I don't see any major visible damage to the cat. I haven't
looked under there yet but I live in New England, so a damaged cat or
exhaust gasket due to corrosion is always a possibility.

One more question. How do I reset the ECU? Do I need to take it back to
the dealer for that or can they do it at AutoZone? Will unplugging the
battery reset the ECU? The dealer did reset the CEL this time an it
hasn't come on in the 50+mi that I have driven so far.

- Manuel.

If P0420 is the only code, my guess is the O2 sensors are OK as they
have their own codes if they go bad.

Not unusual that both cat converters are combined into a single assembly.

With the miles you have on your car it is likely you will experience
the CEL coming on and then go off again. The freq and time the CEL
stays on will increase. That is how mine behaved and light has been
on steady for many months until recently went off for a couple days.

If you attempt to replace the converter yourself, it's not an
extremaly hard job. There are a number of mfgrs now offering cats for
the Subaru. Inquire what the length of the warranty is. Ive' seen
some saying 25k miles and other 50k miles. Prices can run from a
little over $200 to about $750 for a factory replacement. Again if
you do undertake this yourself, DON'T buy a Eastern Catalytic brand.
Not a great fit and front O2 sensor mislocated where it hits the CV
joint. I'm still working on getting my money back on one of these.

Mickey

 

[Edward Hayes]

Many: To reset the ECU, record your radio staling numbers and remove
the negative battery terminal. Press the brake pedal several times to
discharge the ECM fully. Wait another 30 minutes or so and push the
brake peddle again. Reconnect the battery, start the car and let idle
for several minutes( I don't know why). The ECU will be reset to the
original factory specs. The ECU will start logging how you drive from
this point on and eventually average to come up with your driving
type. My gas mileage went down for 2X tank full before returning to my
normal.

 

[Carl 1 Lucky Texan]

You guys have been a great help. Thanks a lot for all the replies.
I will try replacing the forward O2 sensor first and go from there,
assuming I don't see any major visible damage to the cat. I haven't
looked under there yet but I live in New England, so a damaged cat or
exhaust gasket due to corrosion is always a possibility.

One more question. How do I reset the ECU? Do I need to take it back to
the dealer for that or can they do it at AutoZone? Will unplugging the
battery reset the ECU? The dealer did reset the CEL this time an it
hasn't come on in the 50+mi that I have driven so far.

- Manuel.

Sometimes you can talk the A'zone guy into resetting the ECU (they are
reluctant in some states due to emissions testing and especially sales
of used cars. - maybe take him a cold Modelo Especial! If not. Ed's
technique should work.

a good on-line discount dealer for an OEM cat is
www.subarugenuineparts.com Not the only place to shop - just one I have
been happy with. Email Jamie there for any questions. She's great. AND a
Subaru rally racer!

Carl

 

[Sheldon]

Sometimes you can talk the A'zone guy into resetting the ECU (they are
reluctant in some states due to emissions testing and especially sales of
used cars. - maybe take him a cold Modelo Especial! If not. Ed's technique
should work.

a good on-line discount dealer for an OEM cat is
www.subarugenuineparts.com Not the only place to shop - just one I have
been happy with. Email Jamie there for any questions. She's great. AND a
Subaru rally racer!

Carl

You can also buy a code reader that will reset the CEL light for around $50.
I got one just to keep in the car. If the light comes on at least I'll have
an idea whether it's okay to keep driving it. The readers generally give
you a CD or book with a list of codes. You can also find them on the Net.