I just bought a '97 Pontiac Grand Am without a owner’s manual and I’m dieing to know that the “ETS” is. There’s a button on the shifter to turn it on and off but I never feel anything different either way. It doesn’t turn off the overdrive nor does it start the transmission in second gear. What the hell is it?
As mentioned, Traction Control. To try it out, go to a gravel road. Engaged it and floor it. Your car should not (or hardly at all) spin its tires. Its kinda like a pseudo 4x4 in feeling 
. Quite useful in real slippery road conditions.
The dealer when I bought mine told me to turn it on only when necessary (not sure why), which I do, and it seems to work pretty well that way. Although where it is on the gear shift means it gets knocked on and off a lot. I bought mine new and have had almost no problems with it - it’s a great car.
If you try edmunds.com & find your car, you can find the forum for it & talk to other guys with the same car & its a lot of fun.
On my 99 it’s by the hazard lights above the stereo but with mine as soon as I start my car it turns itself on and so I leave it on…besides the trac off light bothers me when I look at my speedometer. So I would imagine that since starting it and the ETS stays on then it doesn’t bother it much…or it hasn’t yet.