2004 Impala security light flashing turn key to start nothing engaged.lights on dash comes on fuses are good.but also my OBD2 scanner can’t link in to the car.
Turn your ignition to the on position. Wait until the Security light stops flashing. (About 5 mins ) then turn back to off. Then try starting.
does your key have a chip in it? If so, do you have a second key can you can use?