* Brake Pedal Position Sensor (Switch): This is the most common culprit. The sensor detects when the brake pedal is pressed and activates the brake lights. If it's faulty, it might stay "on" even when the pedal isn't depressed.
* Brake Light Switch: Similar to the pedal position sensor, but a separate component that can fail.
* Faulty Wiring: A short circuit or break in the wiring leading to the brake lights or the brake light switch could cause the lights to remain illuminated. This could be anywhere between the switch and the lights themselves.
* Master Cylinder: A rare possibility, but a failing master cylinder could sometimes cause issues leading to this symptom. This is more likely accompanied by other problems like spongy brakes or a low brake fluid level.
* Brake Fluid Level: While a low brake fluid level usually triggers a warning light *in addition* to the brake light, a very low level *might* cause this unusual behavior.
Troubleshooting Steps:
1. Check the Brake Fluid Level: Open the hood and locate the brake fluid reservoir. Is the fluid level low? If it is, you have a leak somewhere in the braking system – a serious issue requiring immediate professional attention.
2. Visually Inspect the Wiring: Carefully examine the wiring harness leading from the brake pedal switch to the brake lights. Look for any obvious damage, such as frayed wires, corrosion, or broken connectors.
3. Test the Brake Light Switch (or Pedal Position Sensor): This often requires a multimeter to test the continuity of the switch. If you're not comfortable working with electricity, this is a job best left to a mechanic. Many auto parts stores can test the switch for you.
4. Inspect the Brake Lights Themselves: While less likely to be the *cause*, ensure the brake lights themselves aren't shorted or malfunctioning.
Important Note: Driving with a brake light constantly illuminated is unsafe. It can cause confusion for other drivers and lead to accidents. You should have this problem diagnosed and repaired by a qualified mechanic as soon as possible. Don't attempt major repairs yourself unless you have the proper knowledge and experience.
