Replacing your OEM cats with something aftermarket will always risk your CEL coming on. Replacing just your exhaust from the cats back won't. A tune isn't necessary but will help maximize the gains from your mods. You can also tune your car to stop the CEL light from coming on when you change out your cats.
__________________
Motordyne | Fast Intentions | Berk | Stillen | Amuse | Nismo | Ferrada | Z1 | ZSpeed | Airlift | SPL | EcuTek
|