Woody wrote:
> 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.

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.

> 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.

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.

>
>
> "jim beam" <nospam@example.net> wrote in message
> news:-tSdnUzA2tZufdbZnZ2dnUVZ_tKdnZ2d@speakeasy.net...
>
>>Michael Pardee wrote:
>>
>>>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
>>
>>my experience is yes, it can definitely scratch that itch. with cheapo
>>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.
>
>
>