96 Lexus ES300 - Check Engine Code P0420 (Cat Efficiency)

[Dimitrios Paskoudniakis]

I have a 96 Lexus ES300, with about 135,000 miles. The CEL had been going
on and off intermittently, about once per month, for a couple of days at a
time.

I took the car to the shop, where they diagnosed needing to replace the cat
(P0420 code is cat efficiency). They tested and found O2 sensors fine, and
indicate cat has no ability to store oxygen on rich side. After charging me
almost $200 just to diagnose, wanted almost another $3000 (!!!) to replace
the cat. Even the dealer is closer to $2000.

The shop said they refuse to use aftermarket cats as they are unreliable.

Meanwhile, my car not only runs perfectly fine with no noticeable loss of
power or sluggish accelerator, but my gas mileage has actually improved,
from around 320 miles between fillups (about 13-14 gal) to about 380 miles.
I assume the O2 sensors are telling the system to run lean due to the cat
issue.

Another mechanic tells me as long as there are no symptoms, to live with it
for now.

I am happy to just do nothing for now, but my next state emission test will
be in March 2010. I somehow passed the last one 5 months ago while the
light was intermittent and the test occurred during a light off period. I'm
surprised as the codes are stored and the CEL had been going on and off
prior to the test, but I'll gladly take the test pass.

In the long run, I'll have to address this before my next emission test as I
don't want the cost to buy a car anytime soon, but it's not worth paying
thousands to replace the cat on a now 12-yr old car.

I'm not sure how to proceed, while my car is not only running fine, but
better.

I guess my choices are, before the next emission test, to replace the cat
with an aftermarket cat and take my chances, replace with a genuine Lexus
cat and pay an enormous sum, or ditch the car and buy another one.

Does anyone have any experience with aftermarket cats, which to use or
avoid, or should I not consider? I have also heard from folks who have
taken their cars in for CEL issues, only to have the CEL come back on after
repairs.

I'm not sure what to do. I'd hate to get rid of the car because of this.

[Ray O]

Post by Dimitrios Paskoudniakis
I have a 96 Lexus ES300, with about 135,000 miles. The CEL had been going
on and off intermittently, about once per month, for a couple of days at a
time.
I took the car to the shop, where they diagnosed needing to replace the
cat (P0420 code is cat efficiency). They tested and found O2 sensors
fine, and indicate cat has no ability to store oxygen on rich side. After
charging me almost $200 just to diagnose, wanted almost another $3000
(!!!) to replace the cat. Even the dealer is closer to $2000.
The shop said they refuse to use aftermarket cats as they are unreliable.
Meanwhile, my car not only runs perfectly fine with no noticeable loss of
power or sluggish accelerator, but my gas mileage has actually improved,
from around 320 miles between fillups (about 13-14 gal) to about 380
miles. I assume the O2 sensors are telling the system to run lean due to
the cat issue.
Another mechanic tells me as long as there are no symptoms, to live with
it for now.
I am happy to just do nothing for now, but my next state emission test
will be in March 2010. I somehow passed the last one 5 months ago while
the light was intermittent and the test occurred during a light off
period. I'm surprised as the codes are stored and the CEL had been going
on and off prior to the test, but I'll gladly take the test pass.
In the long run, I'll have to address this before my next emission test as
I don't want the cost to buy a car anytime soon, but it's not worth paying
thousands to replace the cat on a now 12-yr old car.
I'm not sure how to proceed, while my car is not only running fine, but
better.
I guess my choices are, before the next emission test, to replace the cat
with an aftermarket cat and take my chances, replace with a genuine Lexus
cat and pay an enormous sum, or ditch the car and buy another one.
Does anyone have any experience with aftermarket cats, which to use or
avoid, or should I not consider? I have also heard from folks who have
taken their cars in for CEL issues, only to have the CEL come back on
after repairs.
I'm not sure what to do. I'd hate to get rid of the car because of this.

From what I have seen, aftermarket cats are a hit-or-miss proposition.
People have had to replace aftermarket cats 3 or 4 times within a couple of
years, so that doesn't bode well for their durability.

Cats fail because the catalyst substrate becomes coated with particulate
matter over time, and if the exhaust gas can't come in contact with the
catalyst, the gas doesn't get treated. In other words, the catalyst is
still good, but there is no practical way of cleaning the particulate matter
off of the catalyst.

If your car never or only rarely gets highway use, the old adage that it is
good to blow the carbon out still holds. A highway trip gets the cat good
and hot so more of the deposits get burned off and the higher exhaust gas
flow blows stuff out of the tailpipe.

As to what you should do, if you decide to repair the car, have an OEM cat
installed for best results.

[Dimitrios Paskoudniakis]

Post by Ray O

Post by Dimitrios Paskoudniakis
I have a 96 Lexus ES300, with about 135,000 miles. The CEL had been going
on and off intermittently, about once per month, for a couple of days at a
time.
I took the car to the shop, where they diagnosed needing to replace the
cat (P0420 code is cat efficiency). They tested and found O2 sensors
fine, and indicate cat has no ability to store oxygen on rich side.
After charging me almost $200 just to diagnose, wanted almost another
$3000 (!!!) to replace the cat. Even the dealer is closer to $2000.
The shop said they refuse to use aftermarket cats as they are unreliable.
Meanwhile, my car not only runs perfectly fine with no noticeable loss of
power or sluggish accelerator, but my gas mileage has actually improved,
from around 320 miles between fillups (about 13-14 gal) to about 380
miles. I assume the O2 sensors are telling the system to run lean due to
the cat issue.
Another mechanic tells me as long as there are no symptoms, to live with
it for now.
I am happy to just do nothing for now, but my next state emission test
will be in March 2010. I somehow passed the last one 5 months ago while
the light was intermittent and the test occurred during a light off
period. I'm surprised as the codes are stored and the CEL had been going
on and off prior to the test, but I'll gladly take the test pass.
In the long run, I'll have to address this before my next emission test
as I don't want the cost to buy a car anytime soon, but it's not worth
paying thousands to replace the cat on a now 12-yr old car.
I'm not sure how to proceed, while my car is not only running fine, but
better.
I guess my choices are, before the next emission test, to replace the cat
with an aftermarket cat and take my chances, replace with a genuine Lexus
cat and pay an enormous sum, or ditch the car and buy another one.
Does anyone have any experience with aftermarket cats, which to use or
avoid, or should I not consider? I have also heard from folks who have
taken their cars in for CEL issues, only to have the CEL come back on
after repairs.
I'm not sure what to do. I'd hate to get rid of the car because of this.

From what I have seen, aftermarket cats are a hit-or-miss proposition.
People have had to replace aftermarket cats 3 or 4 times within a couple
of years, so that doesn't bode well for their durability.
Cats fail because the catalyst substrate becomes coated with particulate
matter over time, and if the exhaust gas can't come in contact with the
catalyst, the gas doesn't get treated. In other words, the catalyst is
still good, but there is no practical way of cleaning the particulate
matter off of the catalyst.
If your car never or only rarely gets highway use, the old adage that it
is good to blow the carbon out still holds. A highway trip gets the cat
good and hot so more of the deposits get burned off and the higher exhaust
gas flow blows stuff out of the tailpipe.
As to what you should do, if you decide to repair the car, have an OEM cat
installed for best results.
--
Ray O
(correct punctuation to reply)

Thanks. Coincidentally or not, I took a 10 mile ride on the interstate this
afternoon, and later this afternoon the CEL went off.

Also, I live in Maryland, and their emission test program web site indicates
that if the test fails, you get time to make a repair, and if $450 is spent
and the mechanic certifies the repair, if your CEL is still on, you can
apply for a waiver. However, the repair needs to be done within 30 days of
the test, so I'll continue to monitor, and if highway travel keeps the light
from staying on and no other symptoms appear, I'll wait until my next
emission test in January 2010 to do anything.

[Ray O]

Post by Dimitrios Paskoudniakis

Post by Ray O

Post by Dimitrios Paskoudniakis
I have a 96 Lexus ES300, with about 135,000 miles. The CEL had been
going on and off intermittently, about once per month, for a couple of
days at a time.
I took the car to the shop, where they diagnosed needing to replace the
cat (P0420 code is cat efficiency). They tested and found O2 sensors
fine, and indicate cat has no ability to store oxygen on rich side.
After charging me almost $200 just to diagnose, wanted almost another
$3000 (!!!) to replace the cat. Even the dealer is closer to $2000.
The shop said they refuse to use aftermarket cats as they are unreliable.
Meanwhile, my car not only runs perfectly fine with no noticeable loss
of power or sluggish accelerator, but my gas mileage has actually
improved, from around 320 miles between fillups (about 13-14 gal) to
about 380 miles. I assume the O2 sensors are telling the system to run
lean due to the cat issue.
Another mechanic tells me as long as there are no symptoms, to live with
it for now.
I am happy to just do nothing for now, but my next state emission test
will be in March 2010. I somehow passed the last one 5 months ago while
the light was intermittent and the test occurred during a light off
period. I'm surprised as the codes are stored and the CEL had been
going on and off prior to the test, but I'll gladly take the test pass.
In the long run, I'll have to address this before my next emission test
as I don't want the cost to buy a car anytime soon, but it's not worth
paying thousands to replace the cat on a now 12-yr old car.
I'm not sure how to proceed, while my car is not only running fine, but
better.
I guess my choices are, before the next emission test, to replace the
cat with an aftermarket cat and take my chances, replace with a genuine
Lexus cat and pay an enormous sum, or ditch the car and buy another one.
Does anyone have any experience with aftermarket cats, which to use or
avoid, or should I not consider? I have also heard from folks who have
taken their cars in for CEL issues, only to have the CEL come back on
after repairs.
I'm not sure what to do. I'd hate to get rid of the car because of this.

From what I have seen, aftermarket cats are a hit-or-miss proposition.
People have had to replace aftermarket cats 3 or 4 times within a couple
of years, so that doesn't bode well for their durability.
Cats fail because the catalyst substrate becomes coated with particulate
matter over time, and if the exhaust gas can't come in contact with the
catalyst, the gas doesn't get treated. In other words, the catalyst is
still good, but there is no practical way of cleaning the particulate
matter off of the catalyst.
If your car never or only rarely gets highway use, the old adage that it
is good to blow the carbon out still holds. A highway trip gets the cat
good and hot so more of the deposits get burned off and the higher
exhaust gas flow blows stuff out of the tailpipe.
As to what you should do, if you decide to repair the car, have an OEM
cat installed for best results.
--
Ray O
(correct punctuation to reply)

Thanks. Coincidentally or not, I took a 10 mile ride on the interstate
this afternoon, and later this afternoon the CEL went off.
Also, I live in Maryland, and their emission test program web site
indicates that if the test fails, you get time to make a repair, and if
$450 is spent and the mechanic certifies the repair, if your CEL is still
on, you can apply for a waiver. However, the repair needs to be done
within 30 days of the test, so I'll continue to monitor, and if highway
travel keeps the light from staying on and no other symptoms appear, I'll
wait until my next emission test in January 2010 to do anything.

Let us know how you make out.