go away, ses light

I'm hoping some of you longtime Grand Prix owners can give me some input on "service engine soon" lights. Just bought a 2000 GT after having owned exclusively Olds 98s and Park Avenues. In the Olds' I've owned, the ses light always meant one of two things: 02 sensor or EGR valve, both easy fixes. I've had the Grand Prix for two months now, and the light has come on three different times, then goes off on its own. Just today I took it in because the cooling fans were running constantly no matter what the temp gauge said AND the ses light came on. Had the computer reset, the fans don't run constantly now and the light is off. But the mechanic recommended a temp switch, thermostat and coolant flush (yeah, right) even though resetting the computer seemed to solve the problem.

Anyway, I can do the relay switch and thermostat on my own if it's needed, but my question is: what's the typical problem in Grand Prixes when you see the ses light? I love the car, but I think I have a lot of learning to do. I've read that the ses light can point to anything from transmission problems to emissions to the fuel pump. I can't believe the ses light came on because of a problem with the thermostat.

Also, how many people just invest in their own scanner at some point?

Take the car to AutoZone or somewhere and have them scan the car and see what code you've thrown.

Get the code and then you can go from there