Hi XXXXX,
First thing to check would be the brake lamp switch located on a shaft at the top of the brake pedal. These do fail from time to time.
If this helps, please click accept. If you have further questions just drop a note as they are included. Good luck.
Bob
Auto Tech
Plus 40 years GM, over 30 certified with Chevrolet, ASE certified Master Tech. (Expired, Retired)