For injector coding or registration to work you must clear all injector codes, then write each cylinder individually, make sure you cycle the ignition off then on again after each cyl or you will not be able to write the other injectors. If you muck the process up or batt voltage is too low it will fail and you will have to go back to the beginning. This was coding injectors on a yd25 r51 pathfinder but will be the same with D40 Nav etc. It was a very finicky process.