Lux - to really help you, you'd need to get the car scanned. Also, do you feel any misfires or rough idling that is not normal?
Mine began popping on the light after I changed an exhaust manifold. Went to my local Advance Auto for a free scan and they said it was an EGR flow code. Why does the car push a code after being worked on could be as simple as rubbing against a connector gently. I installed a new gasket on my EGR to no avail. The fix seemed to be taking the connector on and off about 5 times.
Please get the code to pop up and have the car scanned.
00 Regal GS: All kinds of cool stuff.