Is a o2 simulator needed with aftermarket exhaust systems/testpipes to prevent a check engine light when the catalytic converter is removed? I sell o2 simulators to the import crowd and am wonder if I should begin marketing towards the GTO crowd as well. The reason I ask is because I've been helping my Dad modify his GTO so I'm starting to get into them (also enjoy driving it too, put on almost 500 miles yesterday!).