To answer your question, yes you can unplug it . IF in fact you have one . Make sure you use a good heavy duct tape to reseal the test port and dont forget to unhook battery to reset computer. Yes you can count codes grounding the STI to any ground point on the car in OBDI for sure if you like counting cryptic flashes and pauses and then never really being sure if you got it right. If you have a fair amount of experience at this then "go for it" but elseways just have a tech pull the codes and then your sure you got it right . You can also buy a code reader at any parts store rangeing from 50 -200 bucks. OBDI the cheapest which is what you have.