Oxygen Sensor for 5KTQ

[SJ]

----- Original Message ----- 
From: "Kneale Brownson" <kneale at coslink.net>


> Why would the sensor need reference air?  It doesn't decide anything, just
> "reports" conditions inside the exhaust system.  I'd think the "reference
> air" if needed, would be at the ECU.   It's the ECU that decides things.
***** The sensor produces a voltage based on the difference in oxygen levels
that exist on both sides of the sensor.
The outside of the sensor is exposed to the exhaust gases(very little
oxygen).
The inside of the sensor is exposed to atmospheric air(reference source)(21%
Oxygen).
This difference in oxygen levels is what produces a corresponding voltage.

The O2 sensor kinda works like your car battery. The voltage produced by the
battery depends on the electrolyte in which the zinc and lead plates are
suspended. When the electrolyte changes(specific gravity), the battery
voltage changes.

In the O2 sensor, think of the exhaust gases as one electrolyte and the
reference air as the other electrolyte. The two gases are held seperate by
the sensor design. The reference air is held constant and the exhaust gases
vary . . .and the sensor output voltage varies.

If you have exhaust gases on both sides of the sensor, there wont be much
voltage produced. Thats why one side(inside) of the sensor is exposed to the
atmosphere, and thats called the "reference air". Why is it exposed to the
atmosphere instead of being sealed with atmospheric air? I suspect its
because there is a small amount of oxidation taking place on the inside of
the sensor . . despite the use of non oxidizing materials. Its hot as hell
in there and some oxidation will take place. Eventually, all the oxygen will
be used up and the O2 sensor wont generate any voltage. Thats why you need a
way to replenish the atmospheric air on the inside of the sensor. How that
air is replaced is the subject of this discussion.

Yes, its the ECU that decides things . .but first it needs to get its input
. .which is a voltage from the O2 sensor. No voltage or the wrong voltage
and the ECU makes the "Limp Home" mode decision  >> purely mechanical
fuel/air adjustments.

SJ





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