Oxygen Sensor on 2003 Accord

highkm wrote in
@c33g2000hsd.googlegroups.com:

> About a month or so ago I got an engine warning light with code P0141
> (2nd bank Oxygen sensor).



P0141 is specifically a heater circuit malfunction in the SECONDARY
(downstream) sensor in the FIRST (front) bank.

Do you have a V6 or 4?



> I continued driving for another 10,000 Kms.
> Did not notice anything i.e. no rough idle, no increase in engine
> heat, oil consumption, and did not notice a reduction in fuel
> efficiency.



You won't notice anything at all, but the engine's computer will.



> Dealer wants$300 to change it. I am not sure there's any
> benefit to it



There isn't really any benefit other than making sure the MIL stays off.



> especially now that I've passed the emissions test even
> with this problem.
>


You passed smog with this? What province are you in? Do they have a dyno
test where you are? Was the MIL illuminated when the car went in?


--
Tegger

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

"Tegger" wrote
> You won't notice anything at all, but the engine's
> computer will.

Didn't Steve H. (the tech?) point out a few years ago that
it's a very minor effect that the downstream O2 sensor has
on fuel emissions yada control? Consistent with what you say
next:

> There isn't really any benefit other than making sure the
> MIL stays off.
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

highkm wrote in



>
> This is a 4 cylinder. This is in Ontario. I have expressed my concerns
> to the mechanic before conducting the emissions test, but did it
> anyways. I was expecting elevated pollution readings, but the test
> came back with zeros in hydro carbons and carbon monoxide.



The heater has no role when an oxygen sensor is up to temp (about 750F).

In any case, the sensor /must/ be up to temp before any emissions test
is performed. One of the technician's jobs is to make sure of that, so
theoretically the O2 sensor heater should not even be a factor in a
DriveClean test.



> I am
> guessing that the computer was able to compensate for the lost sensor



No compensation needed.

The sensor itself is working perfectly. If it were not, you'd get a
different error code.



> - or the issue is a minor one and has negligible effect on the
> emissions. I am not sure if the facility had the dyno test.



If your MIL was on when the car was brought in, the car would have
failed outright. I am guessing yours was off when it was inspected.

The Ontario DriveClean ASM sequence does not involve querying the OBD-II
computer for codes, so your stored code would not have been discovered.


>
> Maybe the wiring on the sensor broke.



Possible, but unlikely. It is, however, the first thing to be checked
before it's decided to replace the sensor. Corrosion on the connector
contacts is also a possibility.

Heater failure is /very/ common. The heater has a difficult job to do.
It is very likely your heater has failed and the sensor needs to be
replaced. It is not possible to replace the heater alone. I would
recommend an OEM sensor depsite the cost. Aftermarket will fail more
often, and more quickly than OEM.



> I am waiting for warmer days to
> check it out. The vehicle has 400K, and I find it strange that a
> sensor would malfunction before some other component that is under a
> lot more stress or is more likely to break after this much mileage.
>



The sensor itself is working fine. O2 sensor heaters ARE highly stressed
components and fail /very/ often.

You don't need to replace it now. If you like you can leave it forever,
so long as you know for sure the MIL is on with only P0141, and so long
as you can always pass smog. And so long as you don't mind the annoyance
of the MIL being on all the time...


--
Tegger

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

As was said that is the secondary o2 sensor. It's only function is to
monitor the efficiency of the catalytic converter. It doesn't control
anything and is compared with the front sensor to make sure the cat is doing
it's job. It is interesting that he passed it because around here any
malfunction will fail the car. Anyway it is a minor fix. Just replace the
sensor. Check auto parts as the dealer will milk you about three times what
it should cost.


"highkm" wrote in message

> About a month or so ago I got an engine warning light with code P0141
> (2nd bank Oxygen sensor). I continued driving for another 10,000 Kms.
> Did not notice anything i.e. no rough idle, no increase in engine
> heat, oil consumption, and did not notice a reduction in fuel
> efficiency. Dealer wants$300 to change it. I am not sure there's any
> benefit to it especially now that I've passed the emissions test even
> with this problem. Does anyone else have a similar problem/experience?
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

On 3/3/2008 5:43 PM Woody spake these words of knowledge:

> As was said that is the secondary o2 sensor. It's only function is to
> monitor the efficiency of the catalytic converter. It doesn't control
> anything and is compared with the front sensor to make sure the cat is doing
> it's job. It is interesting that he passed it because around here any
> malfunction will fail the car. Anyway it is a minor fix. Just replace the
> sensor. Check auto parts as the dealer will milk you about three times what
> it should cost.
>
>
> "highkm" wrote in message
>
>> About a month or so ago I got an engine warning light with code P0141
>> (2nd bank Oxygen sensor). I continued driving for another 10,000 Kms.
>> Did not notice anything i.e. no rough idle, no increase in engine
>> heat, oil consumption, and did not notice a reduction in fuel
>> efficiency. Dealer wants$300 to change it. I am not sure there's any
>> benefit to it especially now that I've passed the emissions test even
>> with this problem. Does anyone else have a similar problem/experience?
Did mine a couple of years ago, when my 2003 Accord 4 cyl had 90-some
thousand miles. The part cost me $57, and I had to get a particular
wrench for the job. All in all, less than $75.


RFT!!!
Dave Kelsen
--
"The individual activity of one man with backbone will do more than a
thousand men with a mere wishbone." -- William J.H. Boetcker
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

"Elle" wrote in
@newsfe06.phx:

> "Tegger" wrote
>> You won't notice anything at all, but the engine's
>> computer will.
>
> Didn't Steve H. (the tech?) point out a few years ago that
> it's a very minor effect that the downstream O2 sensor has
> on fuel emissions yada control?



The secondary O2 sensor can have a small effect on "fine tuning" fuel trim
within a very narrow range. That's intended to damp out any excessively
zealous tendency by the ECM to illuminate the MIL with a P0420.


--
Tegger

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

"Woody" wrote in


> As was said that is the secondary o2 sensor. It's only function is to
> monitor the efficiency of the catalytic converter. It doesn't control
> anything



It does provide a minor input for fuel trim.


--
Tegger

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

"Elle" wrote in


> "Tegger" wrote
>> You won't notice anything at all, but the engine's
>> computer will.
>
> Didn't Steve H. (the tech?) point out a few years ago that
> it's a very minor effect that the downstream O2 sensor has
> on fuel emissions yada control? Consistent with what you say
> next:
>
>> There isn't really any benefit other than making sure the
>> MIL stays off.
>
>
>

AFAIK,the downstream O2S is only for verifying the operation of the
catalytic converter.
They were added as part of the OBD-II diagnostics,OBD-I autos didn't have
them.

--
Jim Yanik
jyanik
at
kua.net
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

Dave Kelsen wrote in


> On 3/3/2008 5:43 PM Woody spake these words of knowledge:
>
>> As was said that is the secondary o2 sensor. It's only function is to
>> monitor the efficiency of the catalytic converter. It doesn't control
>> anything and is compared with the front sensor to make sure the cat
>> is doing it's job. It is interesting that he passed it because around
>> here any malfunction will fail the car. Anyway it is a minor fix.
>> Just replace the sensor. Check auto parts as the dealer will milk you
>> about three times what it should cost.
>>
>>
>> "highkm" wrote in message
>>
>> ...
>>> About a month or so ago I got an engine warning light with code
>>> P0141 (2nd bank Oxygen sensor). I continued driving for another
>>> 10,000 Kms. Did not notice anything i.e. no rough idle, no increase
>>> in engine heat, oil consumption, and did not notice a reduction in
>>> fuel efficiency. Dealer wants$300 to change it. I am not sure
>>> there's any benefit to it especially now that I've passed the
>>> emissions test even with this problem. Does anyone else have a
>>> similar problem/experience?
> Did mine a couple of years ago, when my 2003 Accord 4 cyl had 90-some
> thousand miles. The part cost me $57, and I had to get a particular
> wrench for the job. All in all, less than $75.
>
>
> RFT!!!
> Dave Kelsen

you can borrow the special socket from Advance Auto,other places rent
them,and Harbor Freight sells them very low cost.
I have not heard anything good about Bosch O2 sensors.

--
Jim Yanik
jyanik
at
kua.net
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

Tegger wrote in


> "Woody" wrote in
>
>
>> As was said that is the secondary o2 sensor. It's only function is to
>> monitor the efficiency of the catalytic converter. It doesn't control
>> anything
>
>
>
> It does provide a minor input for fuel trim.
>
>

how could it?
the front O2S adjusts the fuel for the proper ratio,and the cat burns up
anything left.

the 2nd O2S is just for monitoring the cat.

--
Jim Yanik
jyanik
at
kua.net
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

Jim Yanik wrote in
64.209.0.83:

> Tegger wrote in
>
>
>> "Woody" wrote in
>>
>>
>>> As was said that is the secondary o2 sensor. It's only function is to
>>> monitor the efficiency of the catalytic converter. It doesn't control
>>> anything
>>
>>
>>
>> It does provide a minor input for fuel trim.
>>
>>
>
> how could it?
> the front O2S adjusts the fuel for the proper ratio,and the cat burns up
> anything left.
>
> the 2nd O2S is just for monitoring the cat.
>


The ECM monitors the action of the secondary sensor. The ECM is /also/
allowed to "trim" the air/fuel ratio in order to /make/ the secondary
sensor flip-flop properly (or to NOT flip-flop, which is more accurate).

If the ECM is unable to force the secondary sensor into behaving properly
without exceeding the ECM's built-in limits, the ECM will set a P0420.

The reason for this "trim" function is to avoid excessive sensitivity to
P0420 errors.

--
Tegger

The Unofficial Honda/Acura FAQ
www.tegger.com/hondafaq/
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

The ECM cannot force the secondary O2 sensor to do anything. It's output is
only used to compare with the primary sensor to check CAT efficiency which
will generate the P0420 code. The primary O2 sensor is used to control fuel
trim.

"Tegger" wrote in message

> Jim Yanik wrote in
> 64.209.0.83:
>
>> Tegger wrote in
>>
>>
>>> "Woody" wrote in
>>>
>>>
>>>> As was said that is the secondary o2 sensor. It's only function is to
>>>> monitor the efficiency of the catalytic converter. It doesn't control
>>>> anything
>>>
>>>
>>>
>>> It does provide a minor input for fuel trim.
>>>
>>>
>>
>> how could it?
>> the front O2S adjusts the fuel for the proper ratio,and the cat burns up
>> anything left.
>>
>> the 2nd O2S is just for monitoring the cat.
>>
>
>
> The ECM monitors the action of the secondary sensor. The ECM is /also/
> allowed to "trim" the air/fuel ratio in order to /make/ the secondary
> sensor flip-flop properly (or to NOT flip-flop, which is more accurate).
>
> If the ECM is unable to force the secondary sensor into behaving properly
> without exceeding the ECM's built-in limits, the ECM will set a P0420.
>
> The reason for this "trim" function is to avoid excessive sensitivity to
> P0420 errors.
>
> --
> Tegger
>
> The Unofficial Honda/Acura FAQ
> www.tegger.com/hondafaq/
 >> Stay informed about: Oxygen Sensor on 2003 Accord 

Just one bit of evidence to support the contention that
secondary O2 sensors may indeed be used for fine tuning of
fuel trim:

"Engines use either one or two oxygen sensors for fuel
control. Many later model 'V' engines use one sensor to
control each bank independently. This allows for correcting
any bank-to-bank air/fuel deviations or imbalances.
Additional oxygen sensors can be located downstream of the
catalyst. These downstream sensors are used for catalyst
system on-board diagnostics and may often be used for
'fine-tuning' fuel trim."

http://temp.corvetteforum.net/c4/ericfischer/Ford/ford_doc.pdf

More dialogue and documentation on this from Stephen H and
others in 2005: http://amermlrs.com/cars-367.html

"Woody" wrote
> The ECM cannot force the secondary O2 sensor to do
> anything. It's output is only used to compare with the
> primary sensor to check CAT efficiency which will generate
> the P0420 code. The primary O2 sensor is used to control
> fuel trim.
 >> Stay informed about: Oxygen Sensor on 2003 Accord