[Kracka]

W/0 the rear o2 sensor you'll throw a code, but it won't have any performance affects besides a red light staring right back at your face. Cat-back exhausts have nothing to do with the rear o2, it is all in the cat, you'll loose the bung if you get a test-pipe. With a test-pipe you can either live with the light, get an electrical simulator, or make a mechanical simulator