Pontiac Repair: 2005 pontiac bonneville GXP

Question
Keep getting cat. Converter codes , had converter replaced twice -aftermarket converters . Do I need an OEM to stop problem

Answer
Hi Lee:

Aftermarket converters are an issue with every car/truck. if it's not original equipment the calculations the engine control module makes for calculations as to how much hydrocarbons are burned off have to me spot on or the engine control module will keep tripping a code po420 time and time again. You could have an Oxygen sensor issue that causes this but I doubyt it. that engine has 2 a pre and post converter sensor and the difference between what the 2 of them read tells the ecm to turn the right on. there is hope. depending on where you live some states allow used catalytic converters to be sold. if you live in one of them you could be able to get a used one that will work. BUT it has to be from a another GXP a GT or a regular Grand prix will be different. I'll assume this GXP is supercharged correct? if so you need one out of another car with the exact same engine and if you can find one with even less milage on it then yours that is a bonus! Good luck :-)
Just realized you said Bonneville not Grand prix.. The GXP is the 4.6 north star engine. same idea only different engine and car the system works the same BUT the parts need to be an exact match !  Sorry for my Gaff but the end answer is still the same..