My 2003 Chevy Impala has no brake lights. Checked all the fuses, checked the brake switch and bulbs. I do have my 3rd brake light on the top of my trunk and I have all my other lights but no brake lights.
On that year Impala the lower stop lights pull power from the hazard switch and from there to the multi-function switch. You'll need to pull steering column covers and check for power out of the multi-function switch on the yellow and dark green wires.
If you don't have power on either wire, check the turn signal fuse.
If the fuse is OK check for power from the hazard switch to the multi-function switch on the purple wire.
If you have power to the multi-function switch but nothing out, replace the multi-function switch.
If you have power to the hazard switch but nothing out, replace the hazard switch.
If the power side is OK check the ground side at the bulb connector. Pull the bulb and check for ground on the black wire.
If you don't have ground, inspect the harness and repair as necessary.