What is the thin pipe attached to my cat and going up to the engine direction?

I want to remove the cat, dose that pipe have any thing to do with emission control and will removing my cat will fire any engine serves lights?

What do I have to do with the pipe when I remove the cat and replace it with a 3" pipe?

 

It is for emissions control. It pumps air into the cat to make it more efficient. The easiest thing to do would be to remove it from both ends. Since the cat will be completely gone, remove the entire air injection system: tubes, pump, belts, valves. As far as I know, the computer sends signals to the diverter valve, but doesn't expect anything back from it, so removal shouldn't turn on any lights.

 

Actually, you have the single serpentine belt running the pump, I'm sure, so you'll either have to leave the pump in place, get a shorter belt, or get a pulley in there to replace the pump.