Some cars will put that light on to alert to certain maintenance that is supposed to be performed. Otherwise, just stop by an Autozone or similar place and get the code(s) read to see what is going on. It could be just about anything, from a loose gas cap to an oxygen sensor to misfire being detected. Misfire can damage the engine, as has happened sometimes on lifted 4x4 trucks for sale because it can cause pitting of the piston crowns. So let us know what you find out!