Re: how to tell if O2 sensor is Bad...

[Brett Van Sprewenburg <brett@netacc.net>]

>I actually haven't checked scirocco.org for this content but if it isn't
>there (which I doubt) then this will be very interesting to all.  First,
>does anyone know what the 02 sensor actually does?  There is no reference
>signal sent to it so how does it create power?

I would guess like any other battery, a chemical reaction (but with
oxygen) inducing voltage potential between 'ground' and the signal wire?

>It is a bi metal battery.
>It has two metals inside the 02 sensor that creates a voltage.  That is why
>you don't use leaded gas in cars with O2 sensors because it would be adding
>another metal to the system and cause it to die!!

Doesn't the lead just 'bond' to one of the metals (platinum?) so it
doesn't have any more free electrons?

> So, where does it get it's signal?  The 02 sensor is a sensor that 
>compares one thing to another.
>This is the clincher!!!  The O2 sensor compares outside oxygen to the oxygen
>in the exhaust system.  The O2 sensor gets the outside (or atmospheric) air
>through the black wire!!!

I realize that the oxygen has to come from somewhere, but I'm afraid that
even with a powerful pump, you aren't going to be pulling much air
through the insulation tube filled with stranded wire.  Now, maybe you
are referring to the tube which the wires travel through?

>So, if you solder them and wrap them with black
>tape or heat shrink, it won't work correctly!!

Experience would say otherwise here. :)  Having done this several times
with great success, it does indeed work just fine.

>IF you did it correctly,
>bought the correct O2 sensor and used the crimp and heat shrink that it came
>with (if you got the replacement single wire that made to fit almost all
>single wire applications) then you should be fine since the O2 sensor can
>get air through the crimp.

I would debate the use of a butt connector (crimp) on the signal line.
Remember, the voltage potential being sampled is between ground and 1V.
Just about any amount of resistance will degrade this signal.  I believe
that a crimp connection might have a higher potential voltage drop then
a good solder join.  An EE can weigh in with the real deal here as I'm
going on experience and an educated guess.


>And for those of us who are really cheap and use
>used O2 sensors that we find here and there, make sure someone else didn't
>solder it or if you graft it into your harness make sure you use the crimps.
>Bosch used to get thousands of calls on O2 sensors and why they just
>installed one that didn't work so they started coming with crimps and heat
>shrink.  This comes straight from the Bosch class I went to (BAPS1) last
>week.  Since it was kind of a crash course on D, K, K w/lambda, KE, L, LU,
>LE, LH  Jetronic, Motronic, and ABS (all in one week) I don't remember every
>little detail, but I am sure other interesting things will surface as the
>situation calls for it.  HTH!!!
>
>Dave

I appreciate the information Dave, direct from Bosch tech at that. :)  It's
not that I don't believe you or them, but practical experience and what
I thought of basic electronics don't agree with everything you stated.  It
is not uncommon for a company to make something, insist that it be used
in a certain way, state that it won't work any other way, and have people
all over the world happily using it in a way that wasn't intended.

Just trying to provoke a discussion on it...

==Brett

 \/  '84 Scirocco (ITB racer 2B) | "Hot VW's, take two home. They're small"
\/\/ '88 Scirocco 16v (Show), '92 Passat 16v (Winter+) | - brett@netacc.net

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