If your vehicle is showing brake lights don't illuminate when pressing the pedal, here are the most likely causes and the parts you'll need to fix each one.
The mechanical switch located behind the brake pedal can wear out or fail internally over time, preventing the electrical signal from being sent to the brake lights when the pedal is pressed.
A power surge, aging fuse, or a short circuit in the wiring can blow the fuse responsible for the brake light circuit, instantly cutting off power to all brake lamps.
It is common for one bulb to burn out unnoticed, followed eventually by the others. If all bulbs burn out over time, the brake lights will completely fail to illuminate.
If the brake light switch, brake pedal assembly, or brake booster was recently serviced, the switch may have been installed with an incorrect gap, preventing it from registering pedal movement.
In modern vehicles, the brake light switch sends a signal to the BCM, which then commands the lights to turn on. A failing BCM or a software glitch can prevent the lights from illuminating despite a working switch.