I have removed the egr and air smog systems and disabled the circuits by removing the relay and fuses. Then installed headers and catless ypipe and unplugged the post cat 02 sensors. I tried to tune out the codes, which are: PO140, PO160, PO405, PO412, PO418. The codes will delete for the first drive, but all of them come back after turning ignition off and going for the second drive. also, some trouble codes are grayed-out on the list and I cannot unselect them. How do i get around this and get the codes to never come back? should I plug in the rear o2 sensors again, or not necessary? thanks!