O2 sensor controversy again

The question of whether an O2 sensor can be bad enough to cause drivability or fuel economy problems without triggering OBDII codes has another data
point.
In the alt.autos.subaru forum somebody asked for help sorting out very troublesome hesitation after slowing in a 2006 Outback. A respondent had the same problem in his car, and pressured the dealer to do *something*! The dealer replaced the O2 sensor (front one, I presume) in spite of lack of diagnostic codes and the symptom disappeared.
Mike
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Michael Pardee wrote:

aftermarket sensors, my '89, which has a slight tendency to hesitiation anyway, is /way/ worse. no codes. but when i use a new oem sensor, that problem all but disappears.
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Am 89 is not OBDII compliant and does not monitor the sensors that close and the sensors are totally different. The OBDII system monitors heater current and voltage and switching times and voltage to very precisely determine what they are doing. The chance of them causing a problem without setting a code is extremely slim. They can be setting sub codes long before turning on the light on the dash. The information in the computer should be thoroughly analyzed as swapping parts is expensive and could just be masking the real problem.

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experience illustrates it isn't necessarily so. I am puzzled what sort of out-of-the-box defect the sensor would have that would cause it to behave so badly and not be tattled on, though.
Mike
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Michael Pardee wrote:

============================== :-) Maybe the out-of-the-box defect was caused by the BOX ITSELF (like it had the word BOSCH on it)? I keep hearing horror stories about BOSCH, and having owned Volvo and VW, I believe it.
:-(
'Curly'
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Bosch,the new Prince of Darkness? (Lucas being the old one)
--
Jim Yanik
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I won,t believe it until I see it. Of coarse Subaru may have a defect in their OBDII code. Bad enough to cause fuel economy problems you could definitely see on the graph of the sensor.

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I did some Googling on "lazy oxygen sensor" and there were quite a number of articles about the O2S affecting fuel economy.(without setting a code)
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Jim Yanik
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Woody wrote:

monitoring heater current allows determination of element temperature if taken to it's logical limit and simple burn-out at its most basic. other than that, unless it's truly sophisticated, which i doubt in a very noisy electrical environment like under the hood of a car, diagnostics are going to be fairly basic stuff. the primary fault detection mode afaik is to set differential limits between primary and secondary sensors, and trigger if exceeded.

but most people take it to a shop that has testing tools. the obdc computer therefore doesn't need to be that sophisticated. for the home mechanic, and in the absence of these expensive diagnostics, a few parts scavenged from a junk yard, which is where i got the sensors for my comparisons, can be a /much/ cheaper way of determining the level of problem.

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