Why doesn't the engine light go off on my 2001 dodge durango

Which engine light are you referring to? If you are talking about the Check Engine light then it is on because there is a problem with the emissions system. It can be as minor as a loose gas cap or more severe. You need to have the ECU scanned with an OBD2 scan tool. The tool will retrieve the code stored by the ECU. This will tell the technician what part is being effected but not necessarily the defective part. It takes skill and training to determine what the problem is. I suggest you seek out a qualified mechanic with the tools and training and do not just throw parts at the problem.