Re: Replacing O2 sensor in 99 Camry (AF sensors explained)

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Old 14 Oct 2005, 08:24 pm   #1 (permalink)
qslim
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Default Re: Replacing O2 sensor in 99 Camry (AF sensors explained)

Nobody Important <Dr.Xenon1@nospam.gmail.com> wrote:

You know, I've read this before, but it's not clear to me why this is
so. Referring to:

http://www.lindertech.com/docs/j_tho...raf_sensor.pdf

you see on page 20 the transfer function for a plain O2 sensor and on
page 25 that of the fancy toyota sensor. These functions look the same
to me, which implies that you could substitute a plain O2 sensor.
What's wrong with this argument? (I'm not disputing you; I ask merely
for information.)

-------------------

I see what your saying, but pages 20 through 25 explain why a substitution
will not work. It's due to the detection circuit in the ECU, also the
sonstuction of the sensor. An 'old style' sensor is a battery. It produces
voltage based on the amount of oxygen in the exhaust stream. The more
oxygen (lean)the less voltage, the less oxygen (rich) the more voltage. By
cycling the injecor pulse width based on feedback from the primary sensor
output voltage, you are left with what is an ideal stoichiometric average.
Basically, the computer only monitoring a voltage source. The AF sensor
has a fixed voltage output from the computer, and produces current instead
to describe exhaust oxygen content.
To be clear, here is text verbatim from Toyotas own course book;
"Engine Control Systems II - Course 874, Section 7, O2 & A/F Sensor
Diagnosis"......
"The A/F sensor is similar to the O2 sensor. It appears similar to the O2
sensor, but it is constructed differently and has different operating
characteristics.
"The advantage of using the A/F sensor is that the ECM can more
accurately meter the fuel redicing emissions.
"To accomplish this, the A/F sensor:
-operates at app. 650C degrees, much hotter that the O2 sensors which
operate at 400C degrees

-changes its current (amperage) output in relation to the amount of oxygen
in the exhaust stream.

--OPERATION--

"A detection circuit in the ECM detects the change and strength of current
flow and outs out a voltage signal relatively proportional to exhaust
oxygen content.
"This voltage signal can only be measured using the Diagnostic Tester or
OBDII scantool. The AF sensor current output cannot be accurately measured
directly. If a Diagnostic tester or OBDII scantool is used, refer to the
RM for conversion, as the output signal is different.
"The AF sensor is designed so that at stoichiometry, there is no
current flow and the voltage put out by the detection circuit is 3.3
volts. A rich mixture, which leaves very little oxygen in the exhaust
stream, produces a negative current flow. The detection circuit will
produce a voltage below 3.3 volts. A lean mixture, which has more oxygen
in the exhaust stream, produces a positive current flow. The detection
circuit will now produce a voltage signal above 3.3 volts.
"The AF sensor voltage output is the opposite of what happens in the
narrow range O2 sensor. Voltage output through the detection circuit
increases as the mixture gets leaner.
"The AF sensor voltage signal is proportional to the change in the
air/fuel mixture. This allows the ECM to more accurately judge the exact
AF ratio under a wide variety of conditions and quickly adjust the amount
of fuel to the stoichiometric point. This type of rapid correction is not
possible with the narrow range O2 sensor. With an AF sensor, the ECM does
not follow a rich/lean cycle"

--------------

How about that. For those of you with the intestinal fortitude to have
made it this far, you should see now that the main difference in the
system is the detection circuit in the ECM. Since there is no cycling to
bo done in the air/fuel ratio's ECM, a regular galvanic battery-style O2
sensor would not work.
On an interesting side note, there is a crazy wiring diagram in this
course book of the detection circuit inside the ECM for an AF sensor. I
asked the instructor of the course if he could go over it with me (because
it sure as hell makes so sense, I think), and he said that he, as well as
all the other instructors for Central Atlantic Toyota, were not really
clear as to how it works. He told a story of a training conference put on
by engineers in Japan for the Course Instrucors, and when one of fuel
management engineers was asked to explain in detail exactly how the sensor
and detection circuit work, every on was told "There are three people in
Toyota who know how the system works. None of them are here today"
I can scan it if someone has webspace to put it up on. And sorry for
any spelling and grammatical errors, but I'm not going through this long
ass text to edit.


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Old 14 Oct 2005, 11:49 pm   #2 (permalink)
johngdole@hotmail.com
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Default Re: Replacing O2 sensor in 99 Camry (AF sensors explained)

A/F sensor, oxygen sensor are just ways people call a category of
sensors for detecting oxygen content in the exhaust for the purpose of
adjusting the fuel mixture. Bosch for one, call the five different
types of sensors:

1. unheated thimble,
2. heated thimble,
3. planar,
4. wide-band and
5. titania

Check it out:


http://www.boschusa.com/AutoParts/FAQs/OxygenSensors/

Q. Except for the connector assembly, aren't all oxygen sensors
basically the same?
A. NO. There are five fundamentally different types of oxygen sensors:
unheated thimble, heated thimble, planar, wide-band and titania. Within
each sensor type, sensors vary in the design of the ceramic element,
heater element and protection tube design, all of which affect sensor
operation.

Unheated Thimble: This was the first oxygen sensor design and Bosch has
been producing them since 1976. These sensors either have one wire or
two (for purposes of grounding), since they do not require power for a
heater element. They use a zirconia ceramic element to generate a
voltage in a rich (insufficient oxygen) gas environment. They can take
several minutes to reach operating temperatures of 625 degrees
Fahrenheit after a cold start, however this varies with application as
the location of the sensor determines the rate at which it heats. Click
here for a diagram of a thimble type oxygen sensor.

Heated Thimble: These sensors were introduced by Bosch in 1982 and
function in the same manner as the unheated thimble, however inside the
thimble is a special heating element that brings the sensor up to
operating temperature in about 30-60 seconds. The additional wires to
power the heater- typically a total of 3-4 wires (dependent on
grounding scenario) can identify these sensors. Click here for a
diagram of a thimble type oxygen sensor.

Planar: This sensor was introduced by Bosch in 1997 and also uses the
zirconia ceramic sensing technology, but placed in a more compact thin
flat shape (hence the name) instead of a thimble or conical shape. This
allows the sensor to be smaller and lighter. They also require less
electrical power as the heater is integrated into the smaller sensing
element. By model year 2004, planar oxygen sensors are expected to
account for over 30% of all new oxygen sensor applications and by 2007
for over 50% of new oxygen sensors. These sensors also have only four
wires. Click here for a diagram of a planar oxygen sensor.

Wideband: This is the newest design of oxygen sensor and it offers the
increased accuracy needed to meet the latest emissions requirements.
Unlike all the other types of oxygen sensors, the wide-band sensor can
actually measure the air/fuel ratio from 11:1 (excess fuel condition)
all the way to straight air (no fuel)! (The ideal air/fuel ratio is
14.7/1.) This improved measurement allows the engine control system to
measure the actual air/fuel ratio and eliminates the switching between
lean and rich associated with a traditional type of oxygen sensor.
These sensors use a planar zirconia ceramic element, so that they heat
up much faster than other types of sensors- reducing cold start
emissions. These sensors can be identified with having five or more
wires. In addition, these sensors are used with the newly developed
gasoline direct injection engines. Direct injection engines can use
stratified charges, which produce a very lean mixture in the combustion
chamber, and these sensors must be used because of their ability to
measure from very lean to very rich accurately. Click here for a
diagram of a wideband oxygen sensor.

Titania: These sensors use a different type of oxygen sensing
technology and instead of generating a voltage signal that changes with
the air/fuel ratio, the sensor's resistance changes. These sensors
are used on less than 0.5% of all oxygen sensor equipped vehicles.



qslim wrote:
> Nobody Important <Dr.Xenon1@nospam.gmail.com> wrote:
>
> You know, I've read this before, but it's not clear to me why this is
> so. Referring to:
>
> http://www.lindertech.com/docs/j_tho...raf_sensor.pdf
>
> you see on page 20 the transfer function for a plain O2 sensor and on
> page 25 that of the fancy toyota sensor. These functions look the same
> to me, which implies that you could substitute a plain O2 sensor.
> What's wrong with this argument? (I'm not disputing you; I ask merely
> for information.)
>
> -------------------
>
> I see what your saying, but pages 20 through 25 explain why a substitution
> will not work. It's due to the detection circuit in the ECU, also the
> sonstuction of the sensor. An 'old style' sensor is a battery. It produces
> voltage based on the amount of oxygen in the exhaust stream. The more
> oxygen (lean)the less voltage, the less oxygen (rich) the more voltage. By
> cycling the injecor pulse width based on feedback from the primary sensor
> output voltage, you are left with what is an ideal stoichiometric average.
> Basically, the computer only monitoring a voltage source. The AF sensor
> has a fixed voltage output from the computer, and produces current instead
> to describe exhaust oxygen content.
> To be clear, here is text verbatim from Toyotas own course book;
> "Engine Control Systems II - Course 874, Section 7, O2 & A/F Sensor
> Diagnosis"......
> "The A/F sensor is similar to the O2 sensor. It appears similar to the O2
> sensor, but it is constructed differently and has different operating
> characteristics.
> "The advantage of using the A/F sensor is that the ECM can more
> accurately meter the fuel redicing emissions.
> "To accomplish this, the A/F sensor:
> -operates at app. 650C degrees, much hotter that the O2 sensors which
> operate at 400C degrees
>
> -changes its current (amperage) output in relation to the amount of oxygen
> in the exhaust stream.
>
> --OPERATION--
>
> "A detection circuit in the ECM detects the change and strength of current
> flow and outs out a voltage signal relatively proportional to exhaust
> oxygen content.
> "This voltage signal can only be measured using the Diagnostic Tester or
> OBDII scantool. The AF sensor current output cannot be accurately measured
> directly. If a Diagnostic tester or OBDII scantool is used, refer to the
> RM for conversion, as the output signal is different.
> "The AF sensor is designed so that at stoichiometry, there is no
> current flow and the voltage put out by the detection circuit is 3.3
> volts. A rich mixture, which leaves very little oxygen in the exhaust
> stream, produces a negative current flow. The detection circuit will
> produce a voltage below 3.3 volts. A lean mixture, which has more oxygen
> in the exhaust stream, produces a positive current flow. The detection
> circuit will now produce a voltage signal above 3.3 volts.
> "The AF sensor voltage output is the opposite of what happens in the
> narrow range O2 sensor. Voltage output through the detection circuit
> increases as the mixture gets leaner.
> "The AF sensor voltage signal is proportional to the change in the
> air/fuel mixture. This allows the ECM to more accurately judge the exact
> AF ratio under a wide variety of conditions and quickly adjust the amount
> of fuel to the stoichiometric point. This type of rapid correction is not
> possible with the narrow range O2 sensor. With an AF sensor, the ECM does
> not follow a rich/lean cycle"
>
> --------------
>
> How about that. For those of you with the intestinal fortitude to have
> made it this far, you should see now that the main difference in the
> system is the detection circuit in the ECM. Since there is no cycling to
> bo done in the air/fuel ratio's ECM, a regular galvanic battery-style O2
> sensor would not work.
> On an interesting side note, there is a crazy wiring diagram in this
> course book of the detection circuit inside the ECM for an AF sensor. I
> asked the instructor of the course if he could go over it with me (because
> it sure as hell makes so sense, I think), and he said that he, as well as
> all the other instructors for Central Atlantic Toyota, were not really
> clear as to how it works. He told a story of a training conference put on
> by engineers in Japan for the Course Instrucors, and when one of fuel
> management engineers was asked to explain in detail exactly how the sensor
> and detection circuit work, every on was told "There are three people in
> Toyota who know how the system works. None of them are here today"
> I can scan it if someone has webspace to put it up on. And sorry for
> any spelling and grammatical errors, but I'm not going through this long
> ass text to edit.


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Old 15 Oct 2005, 11:27 am   #3 (permalink)
davidj92
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Default Re: Replacing O2 sensor in 99 Camry (AF sensors explained)

johngdole@hotmail.com wrote:
> A/F sensor, oxygen sensor are just ways people call a category of
> sensors for detecting oxygen content in the exhaust for the purpose of
> adjusting the fuel mixture. Bosch for one, call the five different
> types of sensors:


snip

> Titania: These sensors use a different type of oxygen sensing
> technology and instead of generating a voltage signal that changes
> with the air/fuel ratio, the sensor's resistance changes. These
> sensors
> are used on less than 0.5% of all oxygen sensor equipped vehicles.



> qslim wrote:

snip
>> "A detection circuit in the ECM detects the change and strength of
>> current flow and outs out a voltage signal relatively proportional
>> to exhaust oxygen content.

snip

I'm assuming but, it looks like the Bosch Titania O2 sensor is functioning
the same as Toyota's A/F sensor. By changing the resistance in a circuit you
could change the current. Probably Bosch says Potato and Toyota says PotAto.
:-)
davidj92


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Old 18 Oct 2005, 08:48 pm   #4 (permalink)
johngdole@hotmail.com
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Default Re: Replacing O2 sensor in 99 Camry (AF sensors explained)

Toyota calls the wide-band sensor A/F. These are usually twice the cost
of the narrow band ones.

The newer low emissions models I think may have the titania sensor.
These cost over twice the wide-band sensors, like $300-400 a piece.

I'll go with the Bosch wide-band oxygen sensor. I might even try the
one with the universal connector just to see.

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