Check engine light came on yesterday. This is the code I'm coming up with. According to the manual, the downstream sensor operation (as opposed to upstreams), does not affect a/f mixture or fuel injection. BTW, I did put a high flow cat on about 3 weeks ago, but there were no codes at such time. I know that the downstream does monitor post-catalyst o2 levels, so it obviously seems related. The car has been idling very rough, but based upon what info I have, a downstream sensor monitor malfunction shouldn't cause this. I mean, if I replace it, its just going to do the same thing given the high-flow cat. Correct?? Some quality input would be appreciated.

 

Nobody has experience with this ???

 

Time to replace that sensor. (the o2 sensor downstream from the catalytic converter).

 

I understand that, but what I'm saying is that regardless whether I replace it or not, it is going to throw the same code and keep the Check Engine Light on. Besides, the downstream o2 sensor is just a backup in case one of the upstream sensors are down, then it takes the place of them/it and controls actual ratio. Otherwise, and considering you monitor the performance of your vehicle, you shouldn't have a problem.