How can you tell which 02 sensor to replace?

[Zomicon]

Hi guys,

 

Thanks for your help on my car thus far. I got a code for Knock Sensor and 02 sensor on my 97 outback 2.5L. I looked for parts and found there are 2 02 sensors (front and rear). How can you tell which O2 sensor needs replacing? They aren't exactly cheap so I would like to know which one needs replacing before I go to it. Secondly, what do you think about using one of the Bosch universal O2 sensors? I only ask because I am very time constrained and they are in stock, while the model specific ones have to be ordered? Lastly, if you got an O2 sensor code and had to start with one sensor, which one would you start with? I am less concerned about emissions and peak fuel economy at this point and simply concerned with the major dirveability issues that these sensors seem to be causing.

 

Thanks,

 

Zomicon

[frag]

There usually is a specific code for front or rear O2 sensor. Who pulled the code?

If in doubt and unable to have more specific info, the front one is the most important (controls fuel trim) and is most likely to produce driveability issues if out of spec.

Universal sensors are very good but you need to splice them into the existing connector (soldered connections are best). Be sure you get a sensor with the same number of wires than the existing one.

Good luck!