Maybe you need to check the o2 sensor to make sure its not damaged by the person who installed it. Also, when you put a defouler or o2 simulator, did you put it on the right o2 sensor? There are two, Primary and Secondary. If you put it on the Primary, that explains why you are getting the Check Engine Light. Also, make sure the wires are not pulled or damaged during installation because them sob's are easily damaged without the proper tools.