Oxygen Sensor for 5KTQ

Ben Swann benswann at comcast.net
Tue May 10 21:18:51 EDT 2005

Thanks Bob,

As the information here points out - through the sensor shell - or possible through the wiring connector.  It does not say anything about a tube or wire itself carrying the reference O2/air.  I maintain that would not be a good/reliable design.  Unless there is a specific conduit for this purpose, the air is introduced right at the sensor itself.  I have observed little crimp openings as well as holes and identations in some, but never thought as to what they were for, only perhaps part of the manufacturing process.  In theory, just the plain outer casing is enough to provide exposure to reference air - plenty of surface area - and it is al grounded to the exhaust - a lot of surface area.  The little slits on the "thimble" are obvious and they are inside the exhaust, whereas the shell is outside.  That is the difference between the exhaust at thimble slits (inside) and air at casing (outside) that make this operate like a "battery".

Keeping this in mind, I will check some of my vehicles form possible blockage at the sensor itself, as I certainly have not been mindful of this previously.  I have never heard of any problems associated with crimping, soldering, heat shrink wrapping or taping the wire(s) themselves.  If so then almost every car I have maintained has a problem with what I'd consider standard operating procedure.

I suspect some of the newer designs - 4 to 6 wire sensors actually have a dedicated conduit for reference air.  Would be interesting to find out for sure - not being an expert on any of this, I am always like to know more.  I have to admit, eveything I have been reading about these things is nebulous.  Never do you read anything that specifically says - "the reference air is the air that comes directly in contact with the outer casing of the sensor" neither " the reference air is carried by means of a tube that runs inside the wiring sheath" or anything to this effect.


  ----- Original Message ----- 
  From: Robert Myers 
  To: Louis-Alain_Richard at computerhorizons.com ; SJ 
  Cc: quattro-bounces at audifans.com ; quattro at audifans.com ; Ben Swann 
  Sent: Monday, May 09, 2005 12:40 PM
  Subject: Re: Oxygen Sensor for 5KTQ

  From http://www.forparts.com/Bos02update2.htm  The underlining and bold print below is mine and added for emphasis and were not present in the original.  There is a reference signal using O2 from the air.  We have seen this hashed over time and time again.  Here is your answer - direct from Bosch.  There is also a number of Bosch OXS drawings available from a variety of web sites in which the O2 path to the sensor element is clearly visible.

  Unheated Thimble-type O2 Sensors (LS) 

  Bosch introduced this design in 1976 for feedback fuel control on automotive engines. The zirconia ceramic "thimble" is encased in a protective tube which extends into the exhaust manifold.  Slots in the protective tube allow hot exhaust gases to reach the thimble.  Reference outside air for the interior of the thimble comes from a hole in the sensor shell, or through the wiring connector. Unheated O2 sensors rely only on the heat of the exhaust gases to reach operating temperature, therefore they might cool off while the engine is idling and revert back to a fixed air/fuel ratio setting. This type of sensor generally has a single wire connector, though some have two.

  Heated Thimble-type O2 Sensors (LSH)

  Introduced by Bosch in 1982, this sensor adds a heater element to the original design so that the sensor achieves operating temperature in 30-60 seconds, instead of being heated by exhaust gases.  It has a separate electric circuit for the heater, so look for 3 or 4 wire connectors to distinguish this unit.  The heater reduces cold start emissions, as well as prevents the sensor from cooling off at idle.

  At 12:08 PM 5/9/2005, Louis-Alain_Richard at computerhorizons.com wrote:

    *This message was transferred with a trial version of CommuniGate(tm) Pro*

    I remember a strange behaviour from a GM pick-up. When we had it
    oil-sprayed (for corrosion protection), the Check Engine light would lit
    just after, for a couple of days, as if the air surrounding the O2 sensor
    was contaminated by the oily fumes. This was an annual ritual, oil and CEL,
    for as long as we owned that truck. O2 sensor was of the 1 wire variety.


    Solid information on this is hard to find. Air must get in somehow. The
    outside shell shows no openings. And if the openings are so small that you
    cant see them . . .then they are subject to clogging also.
    The only way for air to get in is where the wires come out, or at the
    connector end.

    I brought up this topic hoping someone else knew more than me.
    Then again, maybe this is just an urban myth.


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