toyota o2

[Garfield Willis]

On Wed, 26 Jan 2000 10:51:17 -0500 Scott_Hay at toyota.com

>The Toyota sensor can in fact measure a broad range of a/f ratios but so far,
>there is little information we have in the US as to how it actually works.

Um guys, I've had a look at the pictures of this GReedy gizmo now, Bruce
pointed me to:
	www.suprastore.com/supra/gredairfuelK.html
but have a look Scott at that sensor, and see if it's the one you've
been testing. I have a Toyota WB O2 sensor (cost me nearly $300 just for
the sensor! argh), and it's definitely not the same animal as this one.
Look carefully at the body shape and the probe tip openings. Judging
from the description, I'd have to guess this is actually a conventional
4-wire heated sensor they've attempted to pull a calibration curve for,
on the rich side. If so, it's AFR accuracy is gonna be pretty sloppy.

>The sensor does have 4 wires, B+ for heater, ground for heater - controlled by
>ecm (pwm), afr+ which supplies +3.3v from the ecm to one side of the sensor, and
>afr- which the ecm supplies +3.0v to the other side of the sensor.
>
>We do see a variable voltage when using a scanner tool but when you measure the
>sensor itself, voltage is not moving with major shifts in afr????  The general
>thought is that it  monitors the amperage and the direction of current flow to
>determine the afr. The scan tool voltage is a calculated # to give diagnostic
>functions.

Yup, you're seeing there the behavior of all current-pump style sensors;
you won't see much variation in Vs because there's a feedback loop
in the interface that's intentionally attempting to hold Vs at a fixed
value, while the current thru the pump is varied. It's the oxygen pump
current that reflects the AFR, just as you surmise. In this case, it's
the same two terminals +-afr, so the voltage across them is the Vs while
the current thru them is the pump current.

You've gotta be right about the scanner readout as well; that's AFTER
the interface's pump current is read by the ECU and converted to AFR. 

>Very good and incredibly accurate sensor which operates in a linear fashion to
>afr.
>
>This will probably add more questions than it answers but it is a start.

If this is the sensor GReddy is using, at $285 for the complete system,
it would indeed be a miracle deal. Doubtful, tho; check out the sensor.
If someone can get a look at one of these, the Toyota part number should
be right on the O2 sensor's metal outer jacket. Betcha a donut it's a
conventional 4-wire heated sensor. :)

Gar


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