Ok, the forums have always helped me...got another for you. Service Engine light came on...my car was running rough at idle. After checking the codes, I got misfire in cyl. 1, plus bank 1 sensor 2 (o2) sensor message. My car is federal emissions, not calif. Am I correct in assuming that the sensor it is referring too is on the firewall side of the engine and not the one back towards the Cat? Reason I ask...every time I go to get the part, they ask me if it is the sensor closest to the cat converter. I tell them no, and they look confused. I know there is a pre-cat on the car...but am I missing something here. I only have 3 sensors on the car, I double checked. Also, how hard is it going to be to get to this sensor to remove it?