I have a 01 996 and have noticed CEL comes on every now and then while driving on or off hwy. I don't notice any performance or noise issues when the light is on. It could be a coincidence that CEL comes on when I have around 1/3 fuel and generally goes off when I top off the car and drive for 1or 2 hrs.

Have any of you ever experience this with your car?

 

First thing I would do is read the OBDII codes.....and take it from there.....