P0420 code

[Bilyzoom]

This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace the
rear converter? Does this seem like a fair quote?

2002 Lexus GS300.

[newman]

my local mechanic told me code p0420 was the converter-he said that code was
a converter failure. this was on 99 Accord.

however, the check engine light has since disappeared.
"Bilyzoom" <***@gte.net> wrote in message news:F23ti.97$***@trnddc03...
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace the
rear converter? Does this seem like a fair quote?

2002 Lexus GS300.

[Bilyzoom]

Post by Bilyzoom
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace the
rear converter? Does this seem like a fair quote?
2002 Lexus GS300.
How can does this part fail on a 5 year old car BTW.

[Ray O]

Post by Bilyzoom
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace the
rear converter? Does this seem like a fair quote?
2002 Lexus GS300.

"Bank 1" refers to the cylinder bank that contains Cylinder #1. In the case
of an in-line engine, there is no Bank 2; only Bank 1. I'm pretty sure that
your car has only 1 catalytic converter but it has two O2 sensors - 1 before
the converter and 1 after the converter. The dealer is probably replacing
the catalytic converter and both O2 sensors for that price.

The catalytic converter failure may be covered by the 8 year, 80,000 miles
emissions performance warranty although you may have to pay for the O2
sensors. Ask your service department about emissions warranty coverage.

[Bilyzoom]

Post by Ray O

Post by Bilyzoom
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace the
rear converter? Does this seem like a fair quote?
2002 Lexus GS300.

"Bank 1" refers to the cylinder bank that contains Cylinder #1. In the
case of an in-line engine, there is no Bank 2; only Bank 1. I'm pretty
sure that your car has only 1 catalytic converter but it has two O2
sensors - 1 before the converter and 1 after the converter. The dealer is
probably replacing the catalytic converter and both O2 sensors for that
price.
The catalytic converter failure may be covered by the 8 year, 80,000 miles
emissions performance warranty although you may have to pay for the O2
sensors. Ask your service department about emissions warranty coverage.
--
Ray O
(correct punctuation to reply)

Does this mean I may only need to replace the O2 sensors and not the
catalytic converter. Wouldn't this be a less expensive option to try before
replacing the converter?

[Ray O]

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace the
rear converter? Does this seem like a fair quote?
2002 Lexus GS300.

"Bank 1" refers to the cylinder bank that contains Cylinder #1. In the
case of an in-line engine, there is no Bank 2; only Bank 1. I'm pretty
sure that your car has only 1 catalytic converter but it has two O2
sensors - 1 before the converter and 1 after the converter. The dealer
is probably replacing the catalytic converter and both O2 sensors for
that price.
The catalytic converter failure may be covered by the 8 year, 80,000
miles emissions performance warranty although you may have to pay for the
O2 sensors. Ask your service department about emissions warranty
coverage.
--
Ray O
(correct punctuation to reply)

Does this mean I may only need to replace the O2 sensors and not the
catalytic converter. Wouldn't this be a less expensive option to try
before replacing the converter?

The proper diagnostic procedure is to CHECK both O2 sensors to see if they
are functioning properly before replacing the catalytic converter. If they
appear to be functioning properly, then the catalytic converter is suspect,
and the dealer is probably replacing both O2 sensors to make sure the car
doesn't come back with the same trouble code.

[Bilyzoom]

Post by Ray O

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace
the rear converter? Does this seem like a fair quote?
2002 Lexus GS300.

"Bank 1" refers to the cylinder bank that contains Cylinder #1. In the
case of an in-line engine, there is no Bank 2; only Bank 1. I'm pretty
sure that your car has only 1 catalytic converter but it has two O2
sensors - 1 before the converter and 1 after the converter. The dealer
is probably replacing the catalytic converter and both O2 sensors for
that price.
The catalytic converter failure may be covered by the 8 year, 80,000
miles emissions performance warranty although you may have to pay for
the O2 sensors. Ask your service department about emissions warranty
coverage.
--
Ray O
(correct punctuation to reply)

Does this mean I may only need to replace the O2 sensors and not the
catalytic converter. Wouldn't this be a less expensive option to try
before replacing the converter?

The proper diagnostic procedure is to CHECK both O2 sensors to see if they
are functioning properly before replacing the catalytic converter. If
they appear to be functioning properly, then the catalytic converter is
suspect, and the dealer is probably replacing both O2 sensors to make sure
the car doesn't come back with the same trouble code.
--
Ray O
(correct punctuation to reply)

The dealer never said anything about the sensors. They just checked the code
and said it was a catalytic converter and quoted 2600.00. I just sent the
owner of the shop a e-mail requesting a quote for the O2 sensors. I think I
may get a second opinion. There is new shop across the street from my normal
shop.

[Ray O]

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace
the rear converter? Does this seem like a fair quote?
2002 Lexus GS300.

"Bank 1" refers to the cylinder bank that contains Cylinder #1. In the
case of an in-line engine, there is no Bank 2; only Bank 1. I'm pretty
sure that your car has only 1 catalytic converter but it has two O2
sensors - 1 before the converter and 1 after the converter. The dealer
is probably replacing the catalytic converter and both O2 sensors for
that price.
The catalytic converter failure may be covered by the 8 year, 80,000
miles emissions performance warranty although you may have to pay for
the O2 sensors. Ask your service department about emissions warranty
coverage.
--
Ray O
(correct punctuation to reply)

Does this mean I may only need to replace the O2 sensors and not the
catalytic converter. Wouldn't this be a less expensive option to try
before replacing the converter?

The proper diagnostic procedure is to CHECK both O2 sensors to see if
they are functioning properly before replacing the catalytic converter.
If they appear to be functioning properly, then the catalytic converter
is suspect, and the dealer is probably replacing both O2 sensors to make
sure the car doesn't come back with the same trouble code.
--
Ray O
(correct punctuation to reply)

The dealer never said anything about the sensors. They just checked the
code and said it was a catalytic converter and quoted 2600.00. I just sent
the owner of the shop a e-mail requesting a quote for the O2 sensors. I
think I may get a second opinion. There is new shop across the street from
my normal shop.

How many miles on the car?

[Bilyzoom]

Post by Ray O

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace
the rear converter? Does this seem like a fair quote?
2002 Lexus GS300.

"Bank 1" refers to the cylinder bank that contains Cylinder #1. In
the case of an in-line engine, there is no Bank 2; only Bank 1. I'm
pretty sure that your car has only 1 catalytic converter but it has
two O2 sensors - 1 before the converter and 1 after the converter.
The dealer is probably replacing the catalytic converter and both O2
sensors for that price.
The catalytic converter failure may be covered by the 8 year, 80,000
miles emissions performance warranty although you may have to pay for
the O2 sensors. Ask your service department about emissions warranty
coverage.
--
Ray O
(correct punctuation to reply)

Does this mean I may only need to replace the O2 sensors and not the
catalytic converter. Wouldn't this be a less expensive option to try
before replacing the converter?

The proper diagnostic procedure is to CHECK both O2 sensors to see if
they are functioning properly before replacing the catalytic converter.
If they appear to be functioning properly, then the catalytic converter
is suspect, and the dealer is probably replacing both O2 sensors to make
sure the car doesn't come back with the same trouble code.
--
Ray O
(correct punctuation to reply)

The dealer never said anything about the sensors. They just checked the
code and said it was a catalytic converter and quoted 2600.00. I just
sent the owner of the shop a e-mail requesting a quote for the O2
sensors. I think I may get a second opinion. There is new shop across the
street from my normal shop.

How many miles on the car?
--
Ray O
(correct punctuation to reply)

The car has 115K.

[Ray O]

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom
This code was noted as 'BANK 1 CATALYST EFFICIENCY'. My local Lexus
specialist quoted me $2610.08 for front bank 1 and rear catalytic
converters. If the code refers to bank 1 why would I have to replace
the rear converter? Does this seem like a fair quote?
2002 Lexus GS300.

"Bank 1" refers to the cylinder bank that contains Cylinder #1. In
the case of an in-line engine, there is no Bank 2; only Bank 1. I'm
pretty sure that your car has only 1 catalytic converter but it has
two O2 sensors - 1 before the converter and 1 after the converter.
The dealer is probably replacing the catalytic converter and both O2
sensors for that price.
The catalytic converter failure may be covered by the 8 year, 80,000
miles emissions performance warranty although you may have to pay for
the O2 sensors. Ask your service department about emissions warranty
coverage.
--
Ray O
(correct punctuation to reply)

Does this mean I may only need to replace the O2 sensors and not the
catalytic converter. Wouldn't this be a less expensive option to try
before replacing the converter?

The proper diagnostic procedure is to CHECK both O2 sensors to see if
they are functioning properly before replacing the catalytic converter.
If they appear to be functioning properly, then the catalytic converter
is suspect, and the dealer is probably replacing both O2 sensors to
make sure the car doesn't come back with the same trouble code.
--
Ray O
(correct punctuation to reply)

The dealer never said anything about the sensors. They just checked the
code and said it was a catalytic converter and quoted 2600.00. I just
sent the owner of the shop a e-mail requesting a quote for the O2
sensors. I think I may get a second opinion. There is new shop across
the street from my normal shop.

How many miles on the car?
--
Ray O
(correct punctuation to reply)

The car has 115K.

[Ray O]

"Bilyzoom" <***@gte.net> wrote in message news:DyPui.20568$***@trnddc06...
<snipped>

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom

Post by Ray O

Post by Bilyzoom
Does this mean I may only need to replace the O2 sensors and not the
catalytic converter. Wouldn't this be a less expensive option to try
before replacing the converter?

The proper diagnostic procedure is to CHECK both O2 sensors to see if
they are functioning properly before replacing the catalytic converter.
If they appear to be functioning properly, then the catalytic converter
is suspect, and the dealer is probably replacing both O2 sensors to
make sure the car doesn't come back with the same trouble code.
--
Ray O
(correct punctuation to reply)

The dealer never said anything about the sensors. They just checked the
code and said it was a catalytic converter and quoted 2600.00. I just
sent the owner of the shop a e-mail requesting a quote for the O2
sensors. I think I may get a second opinion. There is new shop across
the street from my normal shop.

How many miles on the car?
--
Ray O
(correct punctuation to reply)

The car has 115K.

Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

[Jay Somerset]

On Thu, 9 Aug 2007 23:27:41 -0500, "Ray O"
<rokigawaATtristarassociatesDOTcom> wrote:

[SNIP]

Post by Ray O
Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

What should the readings be?

[Ray O]

Post by Jay Somerset
On Thu, 9 Aug 2007 23:27:41 -0500, "Ray O"
[SNIP]

Post by Ray O
Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

What should the readings be?
--
Jay (remove dashes for legal email address)

Here is a pretty good explanation of how O2 sensors work and what the
voltages should be:
http://www.aa1car.com/library/o2sensor.htm

[Xplant]

Post by Ray O

Post by Jay Somerset
On Thu, 9 Aug 2007 23:27:41 -0500, "Ray O"
[SNIP]

Post by Ray O
Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

What should the readings be?
--
Jay (remove dashes for legal email address)

Here is a pretty good explanation of how O2 sensors work and what the
http://www.aa1car.com/library/o2sensor.htm
--
Ray O
(correct punctuation to reply)

Great article-- thanks Ray. I have a 1992 SC400 with 190K miles. The O2
sensor has never been replaced but I have no symptoms mentioned in article.
Should I consider to replace as preventative measure?

Appreciate your prolific feedback to this forum.

[Ray O]

Post by Xplant

Post by Ray O

Post by Jay Somerset
On Thu, 9 Aug 2007 23:27:41 -0500, "Ray O"
[SNIP]

Post by Ray O
Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

What should the readings be?
--
Jay (remove dashes for legal email address)

Here is a pretty good explanation of how O2 sensors work and what the
http://www.aa1car.com/library/o2sensor.htm
--
Ray O
(correct punctuation to reply)

Great article-- thanks Ray. I have a 1992 SC400 with 190K miles. The O2
sensor has never been replaced but I have no symptoms mentioned in
article. Should I consider to replace as preventative measure?
Appreciate your prolific feedback to this forum.

If it were my car, I wouldn't worry about it, but if you want, you can
measure O2 sensor voltage and replace if it is only barely within specs.

[Jay Somerset]

On Sat, 11 Aug 2007 10:11:07 -0500, "Ray O"

Post by Ray O

Post by Jay Somerset
On Thu, 9 Aug 2007 23:27:41 -0500, "Ray O"
[SNIP]

Post by Ray O
Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

What should the readings be?
--
Jay (remove dashes for legal email address)

Here is a pretty good explanation of how O2 sensors work and what the
http://www.aa1car.com/library/o2sensor.htm

Thanks -- good reference!

[Ray O]

Post by Jay Somerset
On Sat, 11 Aug 2007 10:11:07 -0500, "Ray O"

Post by Ray O

Post by Jay Somerset
On Thu, 9 Aug 2007 23:27:41 -0500, "Ray O"
[SNIP]

Post by Ray O
Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

What should the readings be?
--
Jay (remove dashes for legal email address)

Here is a pretty good explanation of how O2 sensors work and what the
http://www.aa1car.com/library/o2sensor.htm

Thanks -- good reference!
--
Jay (remove dashes for legal email address)

You're welcome!

[satmech]

Post by Ray O

Post by Jay Somerset
On Sat, 11 Aug 2007 10:11:07 -0500, "Ray O"

Post by Ray O

Post by Jay Somerset
On Thu, 9 Aug 2007 23:27:41 -0500, "Ray O"
[SNIP]

Post by Ray O
Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

What should the readings be?
--
Jay (remove dashes for legal email address)

Here is a pretty good explanation of how O2 sensors work and what the
http://www.aa1car.com/library/o2sensor.htm

Thanks -- good reference!
--
Jay (remove dashes for legal email address)

You're welcome!

P0420 is usually reliable (sorry.)

O2 Sensors have to respond reliably and consistently to their tests to set
this.

cyl 1, 2, 3 => B1
cyl 4, 5, 6 => B2

Look for aftermarket cat. ... they exist.

[Ray O]

Post by satmech

Post by Ray O

Post by Jay Somerset
On Sat, 11 Aug 2007 10:11:07 -0500, "Ray O"

Post by Ray O

Post by Jay Somerset
On Thu, 9 Aug 2007 23:27:41 -0500, "Ray O"
[SNIP]

Post by Ray O
Sorry, you're out of luck on the emissions warranty. If you want to invest
in a volt/ohm meter, you can check out the O2 sensors yourself and see if
they are working properly or not.

What should the readings be?
--
Jay (remove dashes for legal email address)

Here is a pretty good explanation of how O2 sensors work and what the
http://www.aa1car.com/library/o2sensor.htm

Thanks -- good reference!
--
Jay (remove dashes for legal email address)

You're welcome!

P0420 is usually reliable (sorry.)
O2 Sensors have to respond reliably and consistently to their tests to set
this.

I'm not sure what you mean by a "reliable' code. If you check the factory
service manual, you will see the the first step in diagnosing this code is
to check the O2 sensors first.

Post by satmech
cyl 1, 2, 3 => B1
cyl 4, 5, 6 => B2

The OP's car has an in-line configuration - there is no bank 2.

Post by satmech
Look for aftermarket cat. ... they exist.

[j***@hotmail.com]

The dealer is supposed to check for:

1. Make sure the engine is well tuned. If the ignition system is
putting out too much hydrocarbon it will degrade the converters.

2. Check for false air entries in the exhaust system. This can throw
off the oxygen sensors.

3. Oxygen sensors themselves. This is almost impossible as the sensors
can be marginal or even fail and they won't set codes. Being wear
items, I would replace the sensors. In fact, I've fixed a P0420
problem by junking the Denso sensors and using the Bosch Planar type
oxygen sensor. Bosch planars are best-in-class.

http://www.boschautoparts.com/Products/OxygenSensors/PlanarO2.htm

If you can get Bosch planars for your car, go for them. And stay away
from Densos.

3. Then you should consider changing out the converters. Converters
are substrates coated with platinum. Unless they crumble you should be
fine.

$2600. Sheeeeeesh.

Post by Bilyzoom
The dealer never said anything about the sensors. They just checked the code
and said it was a catalytic converter and quoted 2600.00. I just sent the
owner of the shop a e-mail requesting a quote for the O2 sensors. I think I
may get a second opinion. There is new shop across the street from my normal
shop.

[Ray O]

Post by j***@hotmail.com
1. Make sure the engine is well tuned. If the ignition system is
putting out too much hydrocarbon it will degrade the converters.
2. Check for false air entries in the exhaust system. This can throw
off the oxygen sensors.

Air entering the exhaust system will probably set DTC P0125 - insufficient
coolant temperature for closed loop operation.

Post by j***@hotmail.com
3. Oxygen sensors themselves. This is almost impossible as the sensors
can be marginal or even fail and they won't set codes.

Checking the oxygen sensors themselves is very easy with a volt meter or OBD
II scan tool with the capability to display raw sensor output values.

Being wear

Post by j***@hotmail.com
items, I would replace the sensors.

I recommend checking components before replacing them, even if they are wear
items. For example, people would not be happy if a shop replaced brakes or
tires without first checking their condition to see if they need
replacement.

In fact, I've fixed a P0420

Post by j***@hotmail.com
problem by junking the Denso sensors and using the Bosch Planar type
oxygen sensor. Bosch planars are best-in-class.
http://www.boschautoparts.com/Products/OxygenSensors/PlanarO2.htm
If you can get Bosch planars for your car, go for them. And stay away
from Densos.
3. Then you should consider changing out the converters. Converters
are substrates coated with platinum. Unless they crumble you should be
fine.

If the catalyst becomes coated with particulate matter, the exhaust gas does
not come in contact with the catalyst and so the catalyst doesn't do
anything.

[j***@hotmail.com]

Post by Ray O
Air entering the exhaust system will probably set DTC P0125 - insufficient
coolant temperature for closed loop operation.

False air entry into the exhaust is usually seen as a lean condition
(excess presence of oxygen) and will cause ECU to command more fuel.
Why would it set P0125?

Post by Ray O
Checking the oxygen sensors themselves is very easy with a volt meter or OBD
II scan tool with the capability to display raw sensor output values.

I've seen sensor waveforms. I'd think the reaction time waveform need
to correlate with fuel to diagnose slow sensor (and not dead sensors),
which is the problem with many P0420 codes. I've seen people done it
using oscilloscopes with snap-throttle tests, but not sure about the
OBD-II data frames, so I'll leave it to the experts here.

"...while a dead sensor can be detected with a relatively inexpensive
digital volt-ohmmeter, a slow sensor can only be diagnosed by a more
expensive oscilloscope or scope meter."
- Bosch USA

Post by Ray O
I recommend checking components before replacing them, even if they are wear
items. For example, people would not be happy if a shop replaced brakes or
tires without first checking their condition to see if they need
replacement.

Agreed. That why cars need to be well tuned, which is the #1 thing I
mentioned techs should check. But unfortunately, this Toyota (Lexus)
tech didn't even do that, recommending converter changed just based on
a P0420. That's too bad.

Post by Ray O
If the catalyst becomes coated with particulate matter, the exhaust gas does
not come in contact with the catalyst and so the catalyst doesn't do
anything.

Yup, that's why it's so important to keep the engines well tuned!!

Post by Ray O
Ray O
(correct punctuation to reply)

[Ray O]

Post by j***@hotmail.com

Post by Ray O
Air entering the exhaust system will probably set DTC P0125 -
insufficient
coolant temperature for closed loop operation.

False air entry into the exhaust is usually seen as a lean condition
(excess presence of oxygen) and will cause ECU to command more fuel.
Why would it set P0125?

Yes, air entering the exhaust will make the exhaust seem lean, and I don't
know why the ECU sets P0125. For some reason, the factory repair manual
does say to check for an exhaust leak if P0125 comes up, and I have seen
this code caused by exhaust leaks, usually from a loose O2 sensor.

Post by j***@hotmail.com

Post by Ray O
Checking the oxygen sensors themselves is very easy with a volt meter or OBD
II scan tool with the capability to display raw sensor output values.

I've seen sensor waveforms. I'd think the reaction time waveform need
to correlate with fuel to diagnose slow sensor (and not dead sensors),
which is the problem with many P0420 codes. I've seen people done it
using oscilloscopes with snap-throttle tests, but not sure about the
OBD-II data frames, so I'll leave it to the experts here.
"...while a dead sensor can be detected with a relatively inexpensive
digital volt-ohmmeter, a slow sensor can only be diagnosed by a more
expensive oscilloscope or scope meter."
- Bosch USA

A higher end OBD II scanner can compare O2 sensor output. To set P0420,
the ECU compares the signals from the #1 and #2 sensors. When they are
working properly, #1 sensor should have both higher frequency and higher
amplitude than sensor #2 because if the cat is working, sensor #2 shouldn't
see as much activity. If the signal from sensor #2 looks like the signal
from sensor #1, the ECU assumes that the cat isn't working and sets P0420.
If sensor #1 is marginal and not reacting quickly enough, its signal starts
to look like the signal from sensor #2, and if the signals look alike, it
will set the code.

Post by j***@hotmail.com

Post by Ray O
I recommend checking components before replacing them, even if they are wear
items. For example, people would not be happy if a shop replaced brakes or
tires without first checking their condition to see if they need
replacement.

Agreed. That why cars need to be well tuned, which is the #1 thing I
mentioned techs should check. But unfortunately, this Toyota (Lexus)
tech didn't even do that, recommending converter changed just based on
a P0420. That's too bad.

I don't know whether or not the tech checked the signals from the sensor,
and if the sensors were working properly, then the cat is bad. If the tech
checked the sensors, then he should have noted that on the repair order,
although this is not always done. If the tech did not check the sensors,
then that is incomplete or lazy diagnosis.

Post by j***@hotmail.com

Post by Ray O
If the catalyst becomes coated with particulate matter, the exhaust gas does
not come in contact with the catalyst and so the catalyst doesn't do
anything.

Yup, that's why it's so important to keep the engines well tuned!!

I agree, engines should be kept well tuned. Fortunately, modern engines
require very little tuning. Unfortunately, owners often neglect the engines
since there is so little to do.

[j***@hotmail.com]

Yeah. People have said the diagnostics codes are often wrong and one
has to make sure the root of the problem by additional tests. Toyota's
setting P0125 for false air entry and how P0420 sometimes mis-dignoses
the catalytic converter problem are good examples.

Post by Ray O

Post by j***@hotmail.com
False air entry into the exhaust is usually seen as a lean condition
(excess presence of oxygen) and will cause ECU to command more fuel.
Why would it set P0125?

Yes, air entering the exhaust will make the exhaust seem lean, and I don't
know why the ECU sets P0125. For some reason, the factory repair manual
does say to check for an exhaust leak if P0125 comes up, and I have seen
this code caused by exhaust leaks, usually from a loose O2 sensor.

...

Post by Ray O
A higher end OBD II scanner can compare O2 sensor output. To set P0420,
the ECU compares the signals from the #1 and #2 sensors. When they are
working properly, #1 sensor should have both higher frequency and higher
amplitude than sensor #2 because if the cat is working, sensor #2 shouldn't
see as much activity. If the signal from sensor #2 looks like the signal
from sensor #1, the ECU assumes that the cat isn't working and sets P0420.
If sensor #1 is marginal and not reacting quickly enough, its signal starts
to look like the signal from sensor #2, and if the signals look alike, it
will set the code.

[Ray O]

Post by j***@hotmail.com
Yeah. People have said the diagnostics codes are often wrong and one
has to make sure the root of the problem by additional tests. Toyota's
setting P0125 for false air entry and how P0420 sometimes mis-dignoses
the catalytic converter problem are good examples.

It is not that the codes are wrong, I'd say it is more like the descriptions
are not intuitive. The standard codes and the parameter that set them are
determined by the SAE, not the individual automakers.

[j***@hotmail.com]

Yeah, you know, with all the infamous Toyota/Lexus idle air control
valve failures (so much that Toyota gave out free valves but charged
labor -- an arm and a leg), in all cases the ECUs didn't set the P0505
code like it's supposed to.



On Aug 18, 11:17 pm, "Ray O" <rokigawaATtristarassociatesDOTcom>

Post by Ray O
It is not that the codes are wrong, I'd say it is more like the descriptions
are not intuitive. The standard codes and the parameter that set them are
determined by the SAE, not the individual automakers.
--
Ray O
(correct punctuation to reply)

[Ray O]

Post by j***@hotmail.com
Yeah, you know, with all the infamous Toyota/Lexus idle air control
valve failures (so much that Toyota gave out free valves but charged
labor -- an arm and a leg), in all cases the ECUs didn't set the P0505
code like it's supposed to.

A P0505 would be set if there was an open or short in the idle air control
valve circuit. The ECU has no way of knowing if the IAC is gummed up or not
moving enough.

The primary purpose of the OBD II system is to identify if a system that
will affect emissions is malfunctioning. Two common misconception are that
the OBD II system identify every problem with a vehicle, including ones that
affect driveability, and that the component named in the diagnostic trouble
code description must be bad if the code names the component.
Unfortunately, those misconceptions lead people who may be familiar with
older automotive systems but who have not studied the principles behind
automotive on board diagnostic systems to give misguided advice.
--
Ray O
(correct punctuation to reply)

Post by j***@hotmail.com
On Aug 18, 11:17 pm, "Ray O" <rokigawaATtristarassociatesDOTcom>

Post by Ray O
It is not that the codes are wrong, I'd say it is more like the descriptions
are not intuitive. The standard codes and the parameter that set them are
determined by the SAE, not the individual automakers.
--
Ray O
(correct punctuation to reply)

[j***@hotmail.com]

I've cleaned other manufactorer's IAC without a short circuit that was
gummed up and set P0505 like it's supposed to. I guess some ECUs are
not as smart as others in being able to checking engine RPMs changes
while commanding IACs.



On Aug 19, 10:48 pm, "Ray O" <rokigawaATtristarassociatesDOTcom>

Post by Ray O
A P0505 would be set if there was an open or short in the idle air control
valve circuit. The ECU has no way of knowing if the IAC is gummed up or not
moving enough.
The primary purpose of the OBD II system is to identify if a system that
will affect emissions is malfunctioning. Two common misconception are that
the OBD II system identify every problem with a vehicle, including ones that
affect driveability, and that the component named in the diagnostic trouble
code description must be bad if the code names the component.
Unfortunately, those misconceptions lead people who may be familiar with
older automotive systems but who have not studied the principles behind
automotive on board diagnostic systems to give misguided advice.

[Ray O]

Post by j***@hotmail.com
I've cleaned other manufactorer's IAC without a short circuit that was
gummed up and set P0505 like it's supposed to. I guess some ECUs are
not as smart as others in being able to checking engine RPMs changes
while commanding IACs.

I guess not!

[j***@hotmail.com]

No, that's not correct. Some manufacturers measure P0420 with oxygen
store test and some with pre/post sensor waveform test. Conditions
under which tests are run can vary greatly between manufacturers.


On Aug 18, 11:17 pm, "Ray O" <rokigawaATtristarassociatesDOTcom>

Post by Ray O
It is not that the codes are wrong, I'd say it is more like the descriptions
are not intuitive. The standard codes and the parameter that set them are
determined by the SAE, not the individual automakers.
--
Ray O
(correct punctuation to reply)

[Ray O]

Post by j***@hotmail.com
No, that's not correct. Some manufacturers measure P0420 with oxygen
store test and some with pre/post sensor waveform test. Conditions
under which tests are run can vary greatly between manufacturers.

I think we're discussing a difference in semantics. Yes, the conditions
under which tests are run can vary greatly between manufacturers, however,
the code number, description, and parameters are set by the SAE. For P0420,
the **parameter** that sets the code is a bad catalytic converter, and as
you pointed out, there is more than one way to determine whether the
parameter is met or not.