2000 s10 service engine soon light

Ok so i just bought this s10 like two days ago its a great truck 140,000 miles its the zr2 4x4 automatic with the v6 vortex engine. So the SES light came on and i didn't know what to look for. i dont really want to spend money doing a complete diagnosis so i didn't know if the 2000 s10's had a problem that i should start with. any help would be much appreciated. the guy i bought it from said the gas cap would have the light go on so im going to just buy a new cap and see if that works.

Go to your local autoparts store, tell them your check engine light is on, ask if they can pull the codes (most places will do that for free). With out the codes, and no symptoms to work with it is impossible to tell you a good place to start.

If you do replace the fuel cap, don't waste your time or money on aftermarket stuff, get an AC Delco one. When you retrieve the DTC's, post them here in the order they are retrieved.