Hi Jim -- I'm 100% positive there's no negative effect on the engine. I heard this straight from a GM rep and it makes sense. GM doesn't want to sell you something that will sound horrible when AFM kicks in, and they don't want us turning off AFM either. Everyone I've spoken too said it will sound bad with AFM. But the range device takes care of that which as well will not harm anything. Hope this helps let me know if you have any more Q's. Take care, Joe