It will fuck up all of the sensors including O2 sensors temporarily and the car will run like shit until you restart the computer if you use the gas treatment, which with some more modern cars is not even possible. It is GREAT for use in small engines and older boat motors though. If you put it into a modern car you're going to end up worst off than how you started. On the other hand the oil treatment cleans the engine out slick as a whistle, just dont leave it for more than a hundred miles or so before you drain and discard the oil.