You can't do that on 96 and newer vehicles (OBD II), you have to use a scanner. AutoZone will read the codes for free. (Some Advance Autos will, too.) Get the codes and comeback post them so we can help you. Don't listen to the advice given at AutoZone or Advance Auto, those guys are cashiers, not technicians/mechanics. They often cause people to waste a lot of time and money by offering asinine advice and suggesting unneeded repairs.
List of codes:
http://www.automotiveforums.com/vbul...d.php?t=425701