how can I find out whats wrong with my engine when my "check engine" light comes on ?

Ive already searched all around my ecu and cant find that "jumper" that im supposed to "put this thing in" and "push that thing out"

 

http://www.c-speedracing.com/faq.html

 

The jumper is in the front passenger side under the dash. Kinda just look under there on there on the side and it should be tucked in there. It's been awhile, but I think it may have a green rubber thing covering the plug thing. then stick a paper clip into the two holes to short it and then turn the ignition to the on position and the check engine light should flash the codes you need.