Easy, you stick it in the OBD-II port and turn the engine to the On position. Then you navigate to Read Codes and it pulls the codes. It supports reading the Freeze Frame (engine stats at the time of fault), MIL codes and can even pull the VIN# through the OBD-II. I got this Lauinch CReader IV for around $45 shipped on eBay. I also have a Launch CReader II and it functions as well, but just displays the codes. I wish I could afford to get the Launch X-431 Infinite: http://cgi.ebay.com/ebaymotors/Launc...QQcmdZViewItem but it's too pricey for me and I'm not a full time mechanic, but I would love to have it.