Well......I was driving to work this morning and my wife's Dodge Charger CEL came on

(solid on not flashing). Anyway, the car is running flawless and I'm wondering if any of you have ideas of a possible common problem that would cause this. If this is just a hick-up, will the code clear and the light go off? This is the first diagnostic light I’ve had come on so I’m a little worried. I don't normally ask questions about my wife's Charger on here but I respect your opinions
I'm considering buying a diagnostic reader but I don't want to spend a lot of $$$. What do you suggest?