Originally Posted by
JoePoonani
You will get a CEL if you don't have a cat because the secondary o2 sensor is reading dirty air. There are o2 sensor simulators out there that help this issue, but I don't know how reliable those are.
its not reading dirty air at all. the secondary o2 sensor is there to make sure there is a variance between itself, and the primary 02 sensor.
if it sees no variance (a la test pipe, gutted cat, failed catalyst etc) then it activates the CEL.
a simulator (in most cases) places the secondary sensor out of the direct flow of the exhaust maintaining that variance in readings between the two sensors