Well I put on a Borla header, R/T cat-pipe, and custom catback with Magnaflow cans months ago and haven't had any problems till today when my RS threw a CEL. I pulled it with a reader. The code I got (generic of course as I can only dream of the $1000+ Suby specific unit) was P0139- [O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)] Has anyone else had this problem? I know it could be fixed with an O2 eliminator kit, but I'd like to keep the 2nd O2 sensor in the loop if possible. I'm sure one problem is that in it's stock location it was mounted in the second cat where as now it's in the pre-04 position near the donut joint. I did have to extend the sensor wires quite a bit, but I don't think that has anything to do with it. Also oddly enough it was pretty warm out today as opposed to the colder temps of this past winter where I didn't have any problems. As always any and all help is greatly appreciated.

 

Couple things--The second cat will throw a Cat inneficiency CEL, which can be eliminated by the O2 eliminator kit. I believe that is hte only reason for the second O2 sensor, to see if the cat is doing it's job. The first O2 sensor is the one that sends all the info to the computer. I wonder if that code reader is reading the same thing as other code readers, just diffrerent code #s and different explanation? I'm not sure...Brian

 

Thanks Brian and your right. The second O2 is soley to report the condition of the cats. My code reader does have a different code for cat inefficiency. If it threw that code then yea I would have to go with a an O2 eliminator kit. I've driven the car several times since then with out any CEL's so I think I may have a theory. For a hard trouble code to show on an O2 sensor in an OBD II vehicle it has to have the same problem for two consecutive trips. That day I had two trips both of which the car wasn't fully cold before I drove off. The trouble code I got basically means that the second O2 sensor took what the computer deems to long to heat up as compared to the first one. I think this happened because the car was still warm allowing the 1st O2 to heat up right away, but since the 2nd O2 has been relocated from inside the first cat on the OE set-up to all the way down the line almost to the donut joint in the Random Tech set-up it just took to long for it to heat up. At this point it's not a huge problem because it's very easy to pull the code and delete it with the reader. If it does become a nuisance then I'll have to deal with it.