it's the wire coming out of the o2 sensor. tapping into it at the ecu to avoid finding/drilling holes in the firewall is for girls.

 

if my car looked like yours, i would have no problem with drilling holes in the firewall, or anywhere for that matter. besides, you don't have to drill a hole, you can run it through where there is already wires, i just don't want one stray wire hanging out in my engine bay

 

you notice I say finding as well as drilling, I have never drilled a hole in my firewall. just electrical tape the wire up and nobody will know. don't you have a manual for your car? it should have wiring diagrams in there for you to figure out where the wire hooks up to your pos obd2 ecu.

 

nope, no manual, i'm sure i can find it some where via google.

 

thick white wire on the blue connector plug (obd2)