its definitely one of the sensors after the catalytic converter. if it only has one cat... easy enough. if it has 2, youll have to find whitch side manifold they are referring to as bank 1. bank = left or right side. sensor 1= before cat. sensor2 = after cat. oh yeah... if you have one cat., you have 3 02 sensors. if theres 2 cats, you have 4 o2 sensors.