Are all O2 Sensors created equal?

[Brett Dikeman]

At 1:58 PM -0400 6/16/03, SJ&I Santoliquido wrote:

>I have a question about the O2 sensors on my 1996 A6 Wagon. It has 4
>(how did they figure out that 2 wasn't enogh, but 6 would be too
>many?). The two forward ones (close to the engine) are three-wire
>sensors. The two behind the cats are four wire sensors.
>Rod at TPC said the three-wire didn't show up as cross-referenced to
>the Bosch 13913 (universal) in the Bosch catalog. And he didn't know
>a universal for the four wire.
>So I have three questions:
>1) Any BTDT using the 13913 in the front locations (or other
>inexpensive option).
>2) Any inexpensive substitutions for the rear, four-wire ones?
>3) What are the  rear ones there for anyway???

To make sure the catalytic converters are working properly.  The ECU
probably also tailors mixture live to the current status of the cats;
it used to be ECUs just bounced slightly between lean+rich to keep
cats happy.


>4) I thought all O2 sensors were created equal. That is: w/ the
>exception of the end connector aren't all three-wires the same
>etc.???

Not quite.  Usually sensors placed down low are spec'd to be
through-cable-jacket vented; the sensor body is sealed and reference
comes from the cable jacket(which is sealed to the sensor.)  A
regular sensor would quickly break down from exposure to water, road
salt, etc, but the cable-jacket-vented sensor won't, since chances
are the open end of the jacket is well above the 'water line' so to
speak.

4-wire sensors can -sometimes- be wideband sensors, and there are two
kinds of wideband sensors if I remember right.  However, more
commonly 4-wire sensors are used simply to get a good ground
reference.  Two pins for the heater, one for signal, one for signal
ground.  3-wire's are grounded through the exhaust, which is usually
OK.

B
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