i have a 95 z28 and every once in awhile il lbe driving and my ses light will come on and my i can hear my fans running on high then the ses light will shut off along with the fans i have tried to drive to my mechanic quickly once it came on one time to see what the code was but right when i got there the ses light shut off. if anyone knows what could be causing some help would be appreciated

 

The PCM will retain the code, even if the light isn't lit. Have the car scanned and it will show up.

 

From your description, I would bet on an EGR code. Have it scanned, as suggested.