engine computer question

so im told that my car failed it's e-test recently due to the egr valve...but the mechanic (a friend of mine) did some rigorous testing and told me that my computer is in fact not actuating the egr valve, thus giving me a "service engine soon" light almost permanently...he tells me that I need to change the computer...my question is...where is it? and is there a certain model number or code or whatnot I should match up when replacing it? im planning on hittin up a scrap yard a grabbing a few to do this...

never mind this, didnt realize my last thread actually posted