2000 GA GT...service engine light

I just replaced the intake manifold gaskets and all other gaskets for that matter about two weeks ago. No problems with car...no leaks or anything, but then today the service engine light came on. Still no leaks detected and oil isn't milky, so I don't think it is related to the prior service. What all could trigger the light? Any ideas? Car has been running just a little sluggish for a while now.....has 110000 miles.
2000 Grand AM GT 3.4 automatic

The problem could be triggered by anything. It could be a bad O2 sensor or any other number of problems. Take the car to Autozone and have it scanned for codes. Post the code and we'll see what we can do to help.