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.


"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.