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

[drew <drew@dyermaker.cs.uoguelph.ca>]

I'm no expert or tech with 15 years experience in 02 sensors, but it was
my understanding that the platinum element was exposed to air where the
wire enters the sensor housing.  Admittedly I've only ever replaced two O2
sensors, but on both there was a small metal barrel not unlike a crimp
connector that encased the wire as it exited from the ceramic housing -
this seems like a far more likely reliable entry point for reference air
than the end of a light-guage tightly wrapped copper wire that's several
feet away.

Personally, I have trouble believing that Bosch (or any other O2 sensor
manufacturer, for that matter) would have included a crimp connector and
heat shrink tubing to prevent people from soldering O2 sensors in.  I
expect it's more likely that they included the crimp&shrink to keep people
from using wire nuts or just rat-tail splicing the wire and wrapping it in
electrical tape - both being prevalent add-on or replacement wiring fixes
in any older car I've acquired.  If the goal was to prevent soldering,
then they'd probably just slip a little piece of paper in the box that
said "Warning - unreliable O2 sensor operation may result if sensor lead
wire connection is soldered.  Please only use crimp connectors."   That
little piece of paper would be a lot cheaper than the crimp connector and
heat shrink tubing, and would be more likely to accomplish the goal
(presumably reducing calls and warranty claims.)

Mind you, that is my opinion, and it's only backed up by practical
experience and common sense, so please take it at face value.

Drew



On Tue, 27 Mar 2001, Dave Ewing wrote:

> So, how does this NOT support what I said?  Where do you think the "engine
> bay air" comes from?  Is there someplace on the 02 sensor that has a crack
> or a vent hole?  None that I have seen.  Hey, once I heard this, with MY
> experiences with 02 sensors and 15 years of auto tech experience (not to
> mention watching others make mistakes!!), this made way too much sense.  I
> keep hearing about the V drop with a crimp connector and the possibilities
> of corrosion or whatever but this isn't the type of connection that drops .5
> volts or anything.  I would be surprised to see a .01v drop in the type of
> connection that we are talking about.  Plus, my common sense tells me that
> Bosch would not send a crimp and shrink tube with their replacement 02
> sensors if they thought that it would cause problems where they would have
> to be on the hotline answering to unusual 02 sensor failures.  The
> replacement 02 sensors from Bosch (universal) use to come with just a part
> of the insulation stripped off for connection, now they come with the crimp
> and heat shrink.  They did this because people were soldering them and
> having problems.  I am not saying that you will have problems if you solder
> them, the 02 sensor can still get air from other sources (small hole in
> insulation, loosely fitting shrink wrap, etc.) but I am saying they you WILL
> have a higher possiblity for problems if you use a Bosch 02 sensor and
> solder the connection to where it will seal the wire off.  I have done it
> both ways and the crimp works better.  In the BAPS class we actually
> replaced an 02 sensor on one of the cars and the reading on the analog meter
> of the voltage coming from the 02 sensor was perfect.  Used the crimp too!!
> Plus, some fuel systems are digital meaning that the computer converts all
> analog signals to digital.  What this means is that it becomes an on/off
> signal.  So, (and I don't know the specs of where the computer converts)
> this would mean that there is quite a bit of leeway when reading the voltage
> of an 02 sensor.  So, an 02 sensor can alternate between .1v-.9v and the
> computer would be getting the same reading if it were alternating between
> .3v-.7v.  It is where it sticks at one voltage or starts reacting slowly
> that you have a problem.  I have also seen this on cars.  Usually if you
> compare 02 sensor outputs between cars (identical even) they will all be a
> little different.  Anyway, I am not saying you are wrong but you should
> understand that just because you do it and it works, doesn't mean that that
> is the way it was built or meant to work. If you like solder, then solder.
> I prefer crimps.  Easier, quicker, and, according to the manufacturer of the
> item, the correct way.  Just makes more sense to me!
> 
> Dave
> 
> >
> > (Dave? Uh, um no.)
> >
> > Ahem, <cough, cough>
> >
> > OK, here we go!
> >
> > Found at: <http://www.scuderiaciriani.com/rx7/O2_sensor.html>
> > (Don'tcha just love Google :)
> >
> > From: Rob Robinette
> >
> > How the O2 Sensor Works
> >
> > The oxygen sensor detects oxygen in the exhaust in a way similar to a
> > battery cell. Platinum layers on the inside and outside of the probe act
> > as electrodes. Zirconium dioxide between the layers of platinum acts as
> > an electrolyte. The inside layer of platinum is exposed to the air in
> > the engine bay, the outer layer is exposed to the exhaust. When the O2
> > sensor is hot it generates positive voltage between the two layers of
> > platinum. Negatively charged oxygen ions in the exhaust are attracted to
> > the platinum and reduce the voltage that the Engine Control Unit and
> > air/fuel gauge reads.
> >
> > That's why a rich mixture = higher voltage from the sensor (more gas =
> > fewer negative O2 ions to drop the voltage) . Just remember "L=L", Lean
> > = Low voltage. You can attach a Volt Ohm meter (black to ground, red to
> > the O2 sensor) to monitor your engine's air/fuel ratio. Full throttle
> > with 0.82 volts is best performance but slightly higher voltage (richer)
> > is safe. At part throttle the ECU will bounce the ratio from rich to
> > lean. You only have to worry about full throttle. I suggest you have a
> > copilot read the voltage while you accelerate at full throttle.
> >
> > The 3 wire sensors are used to give power and ground to pre-heat the
> > sensor so it starts working quicker, it has no effect after the sensor
> > gets warmed up.
> >
> > ==========  Note: These readings given are in specific context to Mazda
> > RX-7s.======  Lets get some VW specs in here.
> >
> > from the A2 GTI list archives:
> > <http://veedub.nu/a2_16v/archive/1999/May/0147.html>
> >
> > AND Jan's FAQ Web Site! WooHoo!
> > <http://lipari.usc.edu/~jan/vw/Engine/lambda.html>
> > <http://lipari.usc.edu/~jan/vw/Engine/ExhaustAnalyzer>
> >
> > TB: So, the O2 doesn't get it's supply of air down the wire, it's a lot
> > easier than that. You _should_ avoid crimping, (Brett, I'm not an EE,
> > but I play one on T.V.*) Soldering and a suitable shrink wrap or other
> > covering is the way to go. You want to avoid creating any additional
> > load along the signal path, you want to avoid degradation in the future
> > due to oxidation and corrosion. Plus this is why a leaky, cracked gasket
> > or exhaust manifold will through off your mixture.
> > Thems me thinks. But wait! There's More!
> > And this is my last word:
> > <http://lipari.usc.edu/~jan/vw/Engine/oxysensor.html>
> >
> > hth,
> > TBerk
> >
> > *Pops worked on many things when I was young, including the Electron Gun
> > Trigger at S.L.A.C, but me- I never got my General Ed credits together.
> > :( But, I have something on the wall from Hard Knocks U. Int. :]
> >
> > --
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> 
> 
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Drew MacPherson, Network Analyst, University of Guelph

drew@dyermaker.cs.uoguelph.ca           |  visit the Massey-Harris page:
http://dyermaker.cs.uoguelph.ca/~drew   |  http://m-h.cs.uoguelph.ca


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