Oxygen sensor? '90 Celica

I noticed a few weeks ago that while driving at about 55mph. for a few
minutes, my check engine light will come on. When I let go of the gas
pedal, the check engine light will shut off after a few seconds and
will usually remain off for the rest of the night. After reading
through the archives within this group, I came to the conclusion that
it could be my oxygen sensor. I have also noticed that my gas mileage
has dramatically decreased, and from what I also read, is a sign of a
failing oxygen sensor.

I went to have it replaced earlier today and was told that there were
TWO oxygen sensors for my vehicle. I was not able to locate a second
one (there is one before the catalytic converter and according to the
shop I took my vehicle to, there's one after). Is there one or two
oxygen sensors for my vehicle?

Also, if I had the oxygen sensor replaced, would that likely cure the
problem with my intermittent check engine light and decreasing gas
mileage?

Thanks!!

"J" <omnineko@yahoo.com> wrote in message
news:1162317068.489186.213380@e3g2000cwe.googlegroups.com...[color=blue]
>I noticed a few weeks ago that while driving at about 55mph. for a few
> minutes, my check engine light will come on. When I let go of the gas
> pedal, the check engine light will shut off after a few seconds and
> will usually remain off for the rest of the night. After reading
> through the archives within this group, I came to the conclusion that
> it could be my oxygen sensor. I have also noticed that my gas mileage
> has dramatically decreased, and from what I also read, is a sign of a
> failing oxygen sensor.
>
> I went to have it replaced earlier today and was told that there were
> TWO oxygen sensors for my vehicle. I was not able to locate a second
> one (there is one before the catalytic converter and according to the
> shop I took my vehicle to, there's one after). Is there one or two
> oxygen sensors for my vehicle?
>
> Also, if I had the oxygen sensor replaced, would that likely cure the
> problem with my intermittent check engine light and decreasing gas
> mileage?
>
> Thanks!!
>[/color]

The easiest way to tell if there is a second oxygen sensor in your car is to
look under the car. If you see something shaped like a cigar with a wire
attached sticking out of the exhaust pipe after the catalytic converter,
then it has 2 sensors. All vehicles equipped with the OBD II diagnostic
system have O2 sensors before and after the catalytic converter, but your
vehicle is not OBD II.

As far as whether replacing an oxygen sensor is likely to cure the
intermittent check engine light and decreasing fuel mileage, it depends on
what is making the check engine light illuminate. You can greatly increase
the odds that you will check and repair the proper component if you pull the
trouble codes that are likely stored in your car's computer.

Look under the driver's side of the dashboard for a covered connector that
is marked "diag" or "diagnostic." Open the cover, and with a
straightened-out paper clip, connect terminals TE1 and E1. The terminals
will be marked on the connector itself or on the inside of the cover. Turn
the ignition switch on and count the flashes of the check engine light,
noting the short and long pauses between flashes until the pattern starts to
repeat itself. For example, with X representing a flash, XXX (short pause)
X means 41. There may be more than 1 code stored, and each code has 2
digits. Let us know what the codes are, and hopefully, someone will have
the trouble codes for your car so you will have a better idea of what to
look for.

If you are willing to invest in an inexpensive volt/ohm meter (under $25 at
Radio Shack) then you can check your O2 sensor output.
--

Ray O
(correct punctuation to reply)

Thank you for your quick response Ray.

With the engine off, the code was <b>21</b>.

I turned the engine on and received the same code. When I revved the
engine to 2500rpm, I received an additional code of <b>51</b>.

Ray O wrote:[color=blue]
> "J" <omnineko@yahoo.com> wrote in message
> news:1162317068.489186.213380@e3g2000cwe.googlegroups.com...[color=green]
> >I noticed a few weeks ago that while driving at about 55mph. for a few
> > minutes, my check engine light will come on. When I let go of the gas
> > pedal, the check engine light will shut off after a few seconds and
> > will usually remain off for the rest of the night. After reading
> > through the archives within this group, I came to the conclusion that
> > it could be my oxygen sensor. I have also noticed that my gas mileage
> > has dramatically decreased, and from what I also read, is a sign of a
> > failing oxygen sensor.
> >
> > I went to have it replaced earlier today and was told that there were
> > TWO oxygen sensors for my vehicle. I was not able to locate a second
> > one (there is one before the catalytic converter and according to the
> > shop I took my vehicle to, there's one after). Is there one or two
> > oxygen sensors for my vehicle?
> >
> > Also, if I had the oxygen sensor replaced, would that likely cure the
> > problem with my intermittent check engine light and decreasing gas
> > mileage?
> >
> > Thanks!!
> >[/color]
>
> The easiest way to tell if there is a second oxygen sensor in your car is to
> look under the car. If you see something shaped like a cigar with a wire
> attached sticking out of the exhaust pipe after the catalytic converter,
> then it has 2 sensors. All vehicles equipped with the OBD II diagnostic
> system have O2 sensors before and after the catalytic converter, but your
> vehicle is not OBD II.
>
> As far as whether replacing an oxygen sensor is likely to cure the
> intermittent check engine light and decreasing fuel mileage, it depends on
> what is making the check engine light illuminate. You can greatly increase
> the odds that you will check and repair the proper component if you pull the
> trouble codes that are likely stored in your car's computer.
>
> Look under the driver's side of the dashboard for a covered connector that
> is marked "diag" or "diagnostic." Open the cover, and with a
> straightened-out paper clip, connect terminals TE1 and E1. The terminals
> will be marked on the connector itself or on the inside of the cover. Turn
> the ignition switch on and count the flashes of the check engine light,
> noting the short and long pauses between flashes until the pattern starts to
> repeat itself. For example, with X representing a flash, XXX (short pause)
> X means 41. There may be more than 1 code stored, and each code has 2
> digits. Let us know what the codes are, and hopefully, someone will have
> the trouble codes for your car so you will have a better idea of what to
> look for.
>
> If you are willing to invest in an inexpensive volt/ohm meter (under $25 at
> Radio Shack) then you can check your O2 sensor output.
> --
>
> Ray O
> (correct punctuation to reply)[/color]

Thank you for your quick response Ray.

With the engine off, the code was 21.

I turned the engine on and received the same code. When I revved the
engine to 2500rpm, I received an additional code of 51. However, when I
stopped applying the gas pedal, the only code that remained was code
21.

According to my Chilton's manual, code 21 is "OXYGEN SENSOR SIGNAL."
Code 51 is "SWITCH CONDITION SIGNAL."

Now, also according to Chilton's, it says this could be a "short" in
the oxygen sensor. Would simply replacing the oxygen sensor be a safe
bet to resolving this issue or could it be something more serious?

Thanks again!


Ray O wrote:[color=blue]
> "J" <omnineko@yahoo.com> wrote in message
> news:1162317068.489186.213380@e3g2000cwe.googlegroups.com...[color=green]
> >I noticed a few weeks ago that while driving at about 55mph. for a few
> > minutes, my check engine light will come on. When I let go of the gas
> > pedal, the check engine light will shut off after a few seconds and
> > will usually remain off for the rest of the night. After reading
> > through the archives within this group, I came to the conclusion that
> > it could be my oxygen sensor. I have also noticed that my gas mileage
> > has dramatically decreased, and from what I also read, is a sign of a
> > failing oxygen sensor.
> >
> > I went to have it replaced earlier today and was told that there were
> > TWO oxygen sensors for my vehicle. I was not able to locate a second
> > one (there is one before the catalytic converter and according to the
> > shop I took my vehicle to, there's one after). Is there one or two
> > oxygen sensors for my vehicle?
> >
> > Also, if I had the oxygen sensor replaced, would that likely cure the
> > problem with my intermittent check engine light and decreasing gas
> > mileage?
> >
> > Thanks!!
> >[/color]
>
> The easiest way to tell if there is a second oxygen sensor in your car is to
> look under the car. If you see something shaped like a cigar with a wire
> attached sticking out of the exhaust pipe after the catalytic converter,
> then it has 2 sensors. All vehicles equipped with the OBD II diagnostic
> system have O2 sensors before and after the catalytic converter, but your
> vehicle is not OBD II.
>
> As far as whether replacing an oxygen sensor is likely to cure the
> intermittent check engine light and decreasing fuel mileage, it depends on
> what is making the check engine light illuminate. You can greatly increase
> the odds that you will check and repair the proper component if you pull the
> trouble codes that are likely stored in your car's computer.
>
> Look under the driver's side of the dashboard for a covered connector that
> is marked "diag" or "diagnostic." Open the cover, and with a
> straightened-out paper clip, connect terminals TE1 and E1. The terminals
> will be marked on the connector itself or on the inside of the cover. Turn
> the ignition switch on and count the flashes of the check engine light,
> noting the short and long pauses between flashes until the pattern starts to
> repeat itself. For example, with X representing a flash, XXX (short pause)
> X means 41. There may be more than 1 code stored, and each code has 2
> digits. Let us know what the codes are, and hopefully, someone will have
> the trouble codes for your car so you will have a better idea of what to
> look for.
>
> If you are willing to invest in an inexpensive volt/ohm meter (under $25 at
> Radio Shack) then you can check your O2 sensor output.
> --
>
> Ray O
> (correct punctuation to reply)[/color]

Thank you for your quick response Ray.

With the engine off, the code was 21.

I turned the engine on and received the same code. When I revved the
engine to 2500rpm, I received an additional code of 51. However, when I
stopped applying the gas pedal, the only code that remained was code
21.

According to my Chilton's manual, code 21 is "OXYGEN SENSOR SIGNAL."
Code 51 is "SWITCH CONDITION SIGNAL."

Now, also according to Chilton's, it says this could be a "short" in
the oxygen sensor or the oxygen sensor heater. Would simply replacing
the oxygen sensor be a safe bet to resolving this issue or could it be
something more serious?

Thanks again!

Ray O wrote:[color=blue]
> "J" <omnineko@yahoo.com> wrote in message
> news:1162317068.489186.213380@e3g2000cwe.googlegroups.com...[color=green]
> >I noticed a few weeks ago that while driving at about 55mph. for a few
> > minutes, my check engine light will come on. When I let go of the gas
> > pedal, the check engine light will shut off after a few seconds and
> > will usually remain off for the rest of the night. After reading
> > through the archives within this group, I came to the conclusion that
> > it could be my oxygen sensor. I have also noticed that my gas mileage
> > has dramatically decreased, and from what I also read, is a sign of a
> > failing oxygen sensor.
> >
> > I went to have it replaced earlier today and was told that there were
> > TWO oxygen sensors for my vehicle. I was not able to locate a second
> > one (there is one before the catalytic converter and according to the
> > shop I took my vehicle to, there's one after). Is there one or two
> > oxygen sensors for my vehicle?
> >
> > Also, if I had the oxygen sensor replaced, would that likely cure the
> > problem with my intermittent check engine light and decreasing gas
> > mileage?
> >
> > Thanks!!
> >[/color]
>
> The easiest way to tell if there is a second oxygen sensor in your car is to
> look under the car. If you see something shaped like a cigar with a wire
> attached sticking out of the exhaust pipe after the catalytic converter,
> then it has 2 sensors. All vehicles equipped with the OBD II diagnostic
> system have O2 sensors before and after the catalytic converter, but your
> vehicle is not OBD II.
>
> As far as whether replacing an oxygen sensor is likely to cure the
> intermittent check engine light and decreasing fuel mileage, it depends on
> what is making the check engine light illuminate. You can greatly increase
> the odds that you will check and repair the proper component if you pull the
> trouble codes that are likely stored in your car's computer.
>
> Look under the driver's side of the dashboard for a covered connector that
> is marked "diag" or "diagnostic." Open the cover, and with a
> straightened-out paper clip, connect terminals TE1 and E1. The terminals
> will be marked on the connector itself or on the inside of the cover. Turn
> the ignition switch on and count the flashes of the check engine light,
> noting the short and long pauses between flashes until the pattern starts to
> repeat itself. For example, with X representing a flash, XXX (short pause)
> X means 41. There may be more than 1 code stored, and each code has 2
> digits. Let us know what the codes are, and hopefully, someone will have
> the trouble codes for your car so you will have a better idea of what to
> look for.
>
> If you are willing to invest in an inexpensive volt/ohm meter (under $25 at
> Radio Shack) then you can check your O2 sensor output.
> --
>
> Ray O
> (correct punctuation to reply)[/color]

The oxygen sensor is the most often changed good part on the modern
automobile. Have the system analyzed, to determine WHY the sensor is being
contaminated, would be a better solution to your problem. If could be just
a bad spark plug

mike


"J" <omnineko@yahoo.com> wrote in message
news:1162317068.489186.213380@e3g2000cwe.googlegroups.com...
[color=blue]
> Also, if I had the oxygen sensor replaced, would that likely cure the
> problem with my intermittent check engine light and decreasing gas
> mileage?
>
> Thanks!!
>[/color]

"J" <omnineko@yahoo.com> wrote in message
news:1162322547.516207.87970@e64g2000cwd.googlegroups.com...[color=blue]
> Thank you for your quick response Ray.
>
> With the engine off, the code was 21.
>
> I turned the engine on and received the same code. When I revved the
> engine to 2500rpm, I received an additional code of 51. However, when I
> stopped applying the gas pedal, the only code that remained was code
> 21.
>
> According to my Chilton's manual, code 21 is "OXYGEN SENSOR SIGNAL."
> Code 51 is "SWITCH CONDITION SIGNAL."
>
> Now, also according to Chilton's, it says this could be a "short" in
> the oxygen sensor. Would simply replacing the oxygen sensor be a safe
> bet to resolving this issue or could it be something more serious?
>
> Thanks again!
>[/color]

Assuming that the Chilton's list of codes is correct, then there is a pretty
good chance that replacing the oxygen sensor in the exhaust manifold will
cure the problem. You can confirm this by checking the voltage coming from
the O2 sensor, the Chilton's manual should explain how to do this, or you
can gamble and just replace the sensor.

You can get aftermarket O2 sensors for a lot less than an OEM sensor, but
from what I have read, aftermarket O2 sensors seem to have a much shorter
life. Also, aftermarket sensors often require splicing wires. If you
decide to go with an aftermarket sensor, cut the pigtail off of the old O2
sensor and splice the aftermarket sensor to the pigtail so you maintain the
factory connector. The best way to splice the wire is to twist and solder
the connection and then seal with heat shrink tubing. Crimp connections can
fail and cause check engine lights.

You can clear the codes stored in the car's computer by removing the
EFI/main fuse for 60 seconds.
--

Ray O
(correct punctuation to reply)
[color=blue]
>
> Ray O wrote:[color=green]
>> "J" <omnineko@yahoo.com> wrote in message
>> news:1162317068.489186.213380@e3g2000cwe.googlegroups.com...[color=darkred]
>> >I noticed a few weeks ago that while driving at about 55mph. for a few
>> > minutes, my check engine light will come on. When I let go of the gas
>> > pedal, the check engine light will shut off after a few seconds and
>> > will usually remain off for the rest of the night. After reading
>> > through the archives within this group, I came to the conclusion that
>> > it could be my oxygen sensor. I have also noticed that my gas mileage
>> > has dramatically decreased, and from what I also read, is a sign of a
>> > failing oxygen sensor.
>> >
>> > I went to have it replaced earlier today and was told that there were
>> > TWO oxygen sensors for my vehicle. I was not able to locate a second
>> > one (there is one before the catalytic converter and according to the
>> > shop I took my vehicle to, there's one after). Is there one or two
>> > oxygen sensors for my vehicle?
>> >
>> > Also, if I had the oxygen sensor replaced, would that likely cure the
>> > problem with my intermittent check engine light and decreasing gas
>> > mileage?
>> >
>> > Thanks!!
>> >[/color]
>>
>> The easiest way to tell if there is a second oxygen sensor in your car is
>> to
>> look under the car. If you see something shaped like a cigar with a wire
>> attached sticking out of the exhaust pipe after the catalytic converter,
>> then it has 2 sensors. All vehicles equipped with the OBD II diagnostic
>> system have O2 sensors before and after the catalytic converter, but your
>> vehicle is not OBD II.
>>
>> As far as whether replacing an oxygen sensor is likely to cure the
>> intermittent check engine light and decreasing fuel mileage, it depends
>> on
>> what is making the check engine light illuminate. You can greatly
>> increase
>> the odds that you will check and repair the proper component if you pull
>> the
>> trouble codes that are likely stored in your car's computer.
>>
>> Look under the driver's side of the dashboard for a covered connector
>> that
>> is marked "diag" or "diagnostic." Open the cover, and with a
>> straightened-out paper clip, connect terminals TE1 and E1. The terminals
>> will be marked on the connector itself or on the inside of the cover.
>> Turn
>> the ignition switch on and count the flashes of the check engine light,
>> noting the short and long pauses between flashes until the pattern starts
>> to
>> repeat itself. For example, with X representing a flash, XXX (short
>> pause)
>> X means 41. There may be more than 1 code stored, and each code has 2
>> digits. Let us know what the codes are, and hopefully, someone will have
>> the trouble codes for your car so you will have a better idea of what to
>> look for.
>>
>> If you are willing to invest in an inexpensive volt/ohm meter (under $25
>> at
>> Radio Shack) then you can check your O2 sensor output.
>> --
>>
>> Ray O
>> (correct punctuation to reply)[/color]
>[/color]