What's the story with O2 (Oxygen) sensors - two mechanics give different opinions

Here are the details, I have a 1993 Trooper S, manual tranny, with
118K on it. I have never replaced the O2 sensor, even when the light
went on at 90K. Gas mileage seemed fine and no other lights came on.

It just went on for its 120K services and tune at the dealer (I just
moved here and did not know a good shop). Prior to this service I had
done everything the manual said regarding service (oil changes, tires,
60K and 90K services, etc). I did notice some decreased fuel
efficiency at 110K and I asked one dealer mechanic if I should
replace the O2 sensor now (thinking decreased fuel efficiency was sign
a sign the O2 sensor finally was shot). His response was only if the
O2 light AND the check engine light were on simultaneously - otherwise
the O2 sensor is fine. Just for kicks, I asked another dealer
mechanic 3 bays down from the first, and he said it was likely fine
and that the decreased fuel efficiency was a sign that I needed a tune
up and not a new O2 sensor. I opted for a 120K tune-up, in addition
to the 120K service, and they said they would check and reset the O2
sensor instead (replacing it only if needed). When I picked it up the
O2 light stills comes on and they did not mention checking the actual
sensor (it was late and I was in a rush to get home). However, the
car drives great and fuel efficiency *seems* better - but it is early
to tell as I have only driven 50mi on it since I picked it up.

Which one of these mechanics is right - or is there a different answer
altogether regarding O2 sensors. I am curious as I am getting ready
to drive from the Midwest to Yellowstone for summer fieldwork and I
would like to use as little gas as possible. I do have a couple of
days if I need to get a new O2 sensor, but that's it.

Thanks in advance for your help ...

_____________________________________
If replying by email, remove the obvious junk in my address...

If the car is running great and the gas is not just running out quickly.
Don't worry about the O2 sensor. If you notice a problem then get it
replaced.
ronm

John S wrote:
> Here are the details, I have a 1993 Trooper S, manual tranny, with
> 118K on it. I have never replaced the O2 sensor, even when the light
> went on at 90K. Gas mileage seemed fine and no other lights came on.
>
> It just went on for its 120K services and tune at the dealer (I just
> moved here and did not know a good shop). Prior to this service I had
> done everything the manual said regarding service (oil changes, tires,
> 60K and 90K services, etc). I did notice some decreased fuel
> efficiency at 110K and I asked one dealer mechanic if I should
> replace the O2 sensor now (thinking decreased fuel efficiency was sign
> a sign the O2 sensor finally was shot). His response was only if the
> O2 light AND the check engine light were on simultaneously - otherwise
> the O2 sensor is fine. Just for kicks, I asked another dealer
> mechanic 3 bays down from the first, and he said it was likely fine
> and that the decreased fuel efficiency was a sign that I needed a tune
> up and not a new O2 sensor. I opted for a 120K tune-up, in addition
> to the 120K service, and they said they would check and reset the O2
> sensor instead (replacing it only if needed). When I picked it up the
> O2 light stills comes on and they did not mention checking the actual
> sensor (it was late and I was in a rush to get home). However, the
> car drives great and fuel efficiency *seems* better - but it is early
> to tell as I have only driven 50mi on it since I picked it up.
>
> Which one of these mechanics is right - or is there a different answer
> altogether regarding O2 sensors. I am curious as I am getting ready
> to drive from the Midwest to Yellowstone for summer fieldwork and I
> would like to use as little gas as possible. I do have a couple of
> days if I need to get a new O2 sensor, but that's it.
>
> Thanks in advance for your help ...
>
> _____________________________________
> If replying by email, remove the obvious junk in my address...

> Which one of these mechanics is right - or is there a different answer
> altogether regarding O2 sensors. I am curious as I am getting ready
> to drive from the Midwest to Yellowstone for summer fieldwork and I
> would like to use as little gas as possible. I do have a couple of
> days if I need to get a new O2 sensor, but that's it.
>
> Thanks in advance for your help ...
>
> _____________________________________
> If replying by email, remove the obvious junk in my address...
>

Get the voltage specs fromt he Haynes manual for your truck and check it
yourself. If it is alright and that light annoys you, pop out the bulb.
--
____________________
Remove "X" from email address to reply.

http://www.2carpros.com/topics/O2sensor.htm

John S <[email protected]#*$.org> wrote in message news:<[email protected]>...
> Here are the details, I have a 1993 Trooper S, manual tranny, with
> 118K on it. I have never replaced the O2 sensor, even when the light
> went on at 90K. Gas mileage seemed fine and no other lights came on.
>
> It just went on for its 120K services and tune at the dealer (I just
> moved here and did not know a good shop). Prior to this service I had
> done everything the manual said regarding service (oil changes, tires,
> 60K and 90K services, etc). I did notice some decreased fuel
> efficiency at 110K and I asked one dealer mechanic if I should
> replace the O2 sensor now (thinking decreased fuel efficiency was sign
> a sign the O2 sensor finally was shot). His response was only if the
> O2 light AND the check engine light were on simultaneously - otherwise
> the O2 sensor is fine. Just for kicks, I asked another dealer
> mechanic 3 bays down from the first, and he said it was likely fine
> and that the decreased fuel efficiency was a sign that I needed a tune
> up and not a new O2 sensor. I opted for a 120K tune-up, in addition
> to the 120K service, and they said they would check and reset the O2
> sensor instead (replacing it only if needed). When I picked it up the
> O2 light stills comes on and they did not mention checking the actual
> sensor (it was late and I was in a rush to get home). However, the
> car drives great and fuel efficiency *seems* better - but it is early
> to tell as I have only driven 50mi on it since I picked it up.
>
> Which one of these mechanics is right - or is there a different answer
> altogether regarding O2 sensors. I am curious as I am getting ready
> to drive from the Midwest to Yellowstone for summer fieldwork and I
> would like to use as little gas as possible. I do have a couple of
> days if I need to get a new O2 sensor, but that's it.
>
> Thanks in advance for your help ...
>
> _____________________________________
> If replying by email, remove the obvious junk in my address...

"Chris Phillipo" <[email protected]> wrote in message
news:[email protected]...
>
> > Which one of these mechanics is right - or is there a different answer
> > altogether regarding O2 sensors. I am curious as I am getting ready
> > to drive from the Midwest to Yellowstone for summer fieldwork and I
> > would like to use as little gas as possible. I do have a couple of
> > days if I need to get a new O2 sensor, but that's it.
> >
> > Thanks in advance for your help ...
> >
> > _____________________________________
> > If replying by email, remove the obvious junk in my address...
> >
>
> Get the voltage specs fromt he Haynes manual for your truck and check it
> yourself. If it is alright and that light annoys you, pop out the bulb.
> --
> ____________________
> Remove "X" from email address to reply.
Chris, I believe (and I said "believe") if the bulb is removed, the
computer will then cause the engine to run in the "Open or Closed Loop"
mode--cannot remember which is which--that causes the engine to run as if it
was just started, i.e. rich. Kills gas mileage. If I'm wrong, then I may
learn something from you.
I'm like you, tho', in understanding that such lights bother some
people. A similar alternative: cover the lighted cluster area with tape.
(I've even seen some 'mechanics' paint it like flat black.).
If John S. is not hungry, he should have the car repaired properly.
That light is there for good reason, and a good technician w/proper diag.
equipment should be able to find & eliminate the cause. Just my 2 cents'
worth, and often worth every dime!
Have a good 'un. sdlomi

On 7 Jul 2003 12:37:36 -0700, [email protected] wrote:

>http://www.2carpros.com/topics/O2sensor.htm

So carpros seems to be saying, test the O2 sensor and if in doubt,
replace it at higher mileage.

I can't argue with that advice at 118K. You will make up for it in
increased fuel mileage and drivability.

In article <[email protected]> "sdlomi" <[email protected]> writes:
$ Chris, I believe (and I said "believe") if the bulb is removed, the
$computer will then cause the engine to run in the "Open or Closed Loop"
$mode--cannot remember which is which--that causes the engine to run as if it
$was just started, i.e. rich. Kills gas mileage. If I'm wrong, then I may
$learn something from you.

Open loop. A closed loop system is one in which something from the
output is fed back to the input. In this case, the oxygen level in
the exhaust is fed back to the engine computer and used to control
the air/fuel ratio. An open loop system is one in which there is
no feedback.

Closed loop operation allows the air/fuel mixture to be adjusted
to maintain efficient operation. Open loop does not; the mixture
is hard-coded. You'll burn more gas (i.e. wasting money and
causing more pollution) in open loop operation.

$ If John S. is not hungry, he should have the car repaired properly.
$That light is there for good reason, and a good technician w/proper diag.
$equipment should be able to find & eliminate the cause. Just my 2 cents'
$worth, and often worth every dime!

Ditto. If the check engine light is on because the engine
is running in open loop mode due to an oxygen sensor failure,
your engine is not running as efficiently as it should; you'll
burn more gas. The best solution is to replace the failed
oxygen sensor. The engine computer will have recorded a code
to indicate what is wrong, and while engine management is
extremely complex, a failed oxygen sensor should be a fairly
routine diagnosis.
--
..--------------------------------------. [email protected]
|Silver, perpetually searching for SNTF|------------------------------
`--------------------------------------' a vaguely phallic .signature

[email protected] (Hi Ho Silver) wrote in message

>
> Ditto. If the check engine light is on because the engine
> is running in open loop mode due to an oxygen sensor failure,
> your engine is not running as efficiently as it should; you'll
> burn more gas. The best solution is to replace the failed
> oxygen sensor. The engine computer will have recorded a code
> to indicate what is wrong, and while engine management is
> extremely complex, a failed oxygen sensor should be a fairly
> routine diagnosis.
_______________

EEEEYIPPPEYYYIYYYOO KAYAAAYYEEE!!!!

Sorry...Your screen name was begging for it!

Any how - yesterday I had my 5th out of 8 "Check Engine" notifications
since 9/2001 diagnosed and fixed. 1996 4cyl Contour. **The other 3 I
reset by disconnecting battery**

The OBDII reading was "inefficient cat - operating outside
parameters". I asked my mech what that could indicate and he
shrugged: "anything!"". He suggested a test drive and checking both
02 sensors. Turns out the post 02(after the Cat) was bad, and
replaced it. Car runs smoother now, will not know if it helped
mileage until a week from now. Does his diag. sound correct?

-CC

On 16 Jul 2003 09:49:56 -0700, [email protected] (ChrisCoaster) wrote:

<snip>

>Any how - yesterday I had my 5th out of 8 "Check Engine" notifications
>since 9/2001 diagnosed and fixed. 1996 4cyl Contour. **The other 3 I
>reset by disconnecting battery**
>
>The OBDII reading was "inefficient cat - operating outside
>parameters". I asked my mech what that could indicate and he
>shrugged: "anything!"". He suggested a test drive and checking both
>02 sensors. Turns out the post 02(after the Cat) was bad, and
>replaced it. Car runs smoother now, will not know if it helped
>mileage until a week from now. Does his diag. sound correct?
>
>-CC

This should have no effect on gas mileage as the post cat O2 is only
used for Catalytic converter diagnosis.

In article <[email protected]>, [email protected] says...
> In article <[email protected]> "sdlomi" <[email protected]> writes:
> $ Chris, I believe (and I said "believe") if the bulb is removed, the
> $computer will then cause the engine to run in the "Open or Closed Loop"
> $mode--cannot remember which is which--that causes the engine to run as if it
> $was just started, i.e. rich. Kills gas mileage. If I'm wrong, then I may
> $learn something from you.
>

If the car runs like crap up to around 3000 rpm and then it suddenly
leaps to life then it is almost certainly the O2 sensor, because beyond
a certain RPM it stops reading from it. The last one I had go bad the
engine would run like a lame dog and get worse right up to 3000 RPM,
almost stalling, then it would suddenly go wide open, just about putting
me into the traffic ahead several times. When I put a meter on the O2
sensor the voltage did not match the book at all, I believe mine was
contaminated with antifreze because the head gasket let go a few months
later.
--
____________________
Remove "X" from email address to reply.

On Wed, 16 Jul 2003 23:17:24 -0300, Chris Phillipo
<[email protected]> wrote:

>
>If the car runs like crap up to around 3000 rpm and then it suddenly=20
>leaps to life then it is almost certainly the O2 sensor, because beyond=20
>a certain RPM it stops reading from it.

Don't you believe it.

It is only ignored at cold start, and WOT. And even that is not ALWAYS
the case.

> The last one I had go bad the=20
>engine would run like a lame dog and get worse right up to 3000 RPM,=20
>almost stalling, then it would suddenly go wide open, just about putting=
=20
>me into the traffic ahead several times. When I put a meter on the O2=20
>sensor the voltage did not match the book at all, I believe mine was=20
>contaminated with antifreze because the head gasket let go a few months=20
>later.

saeengineer <[email protected]> writes:

> On Wed, 16 Jul 2003 23:17:24 -0300, Chris Phillipo
> <[email protected]> wrote:
>
> >
> >If the car runs like crap up to around 3000 rpm and then it suddenly
> >leaps to life then it is almost certainly the O2 sensor, because beyond
> >a certain RPM it stops reading from it.
>
> Don't you believe it.
>
> It is only ignored at cold start, and WOT. And even that is not ALWAYS
> the case.

Doesn't that depend on the engine control strategy? This sounds like
they are trying to use the O2 sensor only in the EPA test, and
switching to open loop when they leave that regime.

<snip>

--
-Stephen H. Westin
Any information or opinions in this message are mine: they do not
represent the position of Cornell University or any of its sponsors.

On 17 Jul 2003 13:36:45 -0400, westin*[email protected]
(Stephen H. Westin) wrote:

>saeengineer <[email protected]> writes:
>
>> On Wed, 16 Jul 2003 23:17:24 -0300, Chris Phillipo
>> <[email protected]> wrote:
>>=20
>> >
>> >If the car runs like crap up to around 3000 rpm and then it suddenly=20
>> >leaps to life then it is almost certainly the O2 sensor, because =
beyond=20
>> >a certain RPM it stops reading from it.
>>=20
>> Don't you believe it.
>>=20
>> It is only ignored at cold start, and WOT. And even that is not =
ALWAYS
>> the case.
>
>Doesn't that depend on the engine control strategy? This sounds like
>they are trying to use the O2 sensor only in the EPA test, and
>switching to open loop when they leave that regime.
>

Basically the O2 sensor is used to keep the mixture in line for the
converter to work effectively.

Under WOT the driver is demanding maximum power and ignoring the O2 is
the way to achieve this. On cold start, the O2 sensor is not yet warm
enough to produce an accurate signal so it is ignored at this time also.

> >
>
> Basically the O2 sensor is used to keep the mixture in line for the
> converter to work effectively.
>
> Under WOT the driver is demanding maximum power and ignoring the O2 is
> the way to achieve this. On cold start, the O2 sensor is not yet warm
> enough to produce an accurate signal so it is ignored at this time also.
>

It won't ignore it under WOT until it reaches a preset RPM on every
(Japanese) engine I've seen.
--
____________________
Remove "X" from email address to reply.

On Sat, 19 Jul 2003 13:39:38 -0300, Chris Phillipo
<[email protected]> wrote:

>
>> >
>>=20
>> Basically the O2 sensor is used to keep the mixture in line for the
>> converter to work effectively.
>>=20
>> Under WOT the driver is demanding maximum power and ignoring the O2 is
>> the way to achieve this. On cold start, the O2 sensor is not yet warm
>> enough to produce an accurate signal so it is ignored at this time =
also.
>>=20
>
>It won't ignore it under WOT until it reaches a preset RPM on every=20
>(Japanese) engine I've seen.

Well, that proves it then.