Went to lunch today at work and my check engine light came on. Car has been sluggish and not feeling right. I just had my catback exhaust put on last week and now this happens. Trying to find more info on what's going on.

I had the car scanned at Autozone and I got a p0139 code which read rear oxygen sensor circuit slow response.

...anyone have any expierence or knowledge with this and what the fix could be? Gonna get a new o2 sensor if need be from work, but I dont want this to happen again.

Is this a Subaru or a Mitsu that we are talking about, here...???

According to the Subaru FSM, replacing it is the only fix.

I get that code on and off with my catless setup. I'll be switching to a high-flow cat downpipe when I secure the funds.