Check Engine Light

2002 Ford Ranger(44m Miles): After Filling The Gas Tank The Next Day I Noticed The Fuel Gauge Was Malfunctioning (posting Beyond Full). That Afternoon My Check Engine Light Came On. I Suspect The Gas Cap But Not Familiar Whether Or Not This Can Be A Common Problem.

Can you go by a AutoZone and let them read the alpha-numeric code?

They will want to tell you what is "wrong", but insist on getting the code(s). It will be something of this form: P0231.