Check Engine Light

I have a 1997 Pontiac Sunfire with a 2.2 Liter engine and an automatic transmission..The problem is my CEL stays on all the time and I can hook an Actron Scanner to it and it doesn't read any codes out at all,but I can reset the light with the Scan Tool and it will go off for about 100 miles and then it comes back on and stays on again....The car runs good and gets good gas milage,but sometimes in the mornings when I start the car it will backfire through the tailpipe a couple of times and after that it runs really good..any help appreciated...

Leave the scanner hooked up while you are driving. Some codes will clear when you restart the car or once you shut the key off. I would clear the code and drive the car and see what happens. If the light comes on there has to be a problem somewhere.