Brake Lights Not Working? Let’s Put a Stop to That

Mia Bevacqua
February 15, 2018

To avoid getting rear-ended, it’s important to have brake lights that work. They’re the primary way you tell the drivers behind you that you’re slowing down or stopping. If one or more of your brake lights isn’t working, don’t despair — there’s a solution. It could be as simple as replacing a fuse or bulb, or you might need help from a professional mechanic.

brake lights not working

Of course, it can be hard to tell if your brake lights aren’t working. The easiest way is to ask a friend to watch them while you press the brakes while parked at home. To check them yourself, with the engine on and car in park, you can wedge a broom handle or heavy block so that it presses the brake pedal, and then walk back and check them. Or, if you’re in a safe spot, you can rig your phone to take a video while you press the brakes. If they don’t light up, it’s time for a repair.

How your brake lights work

The brake lights are triggered by a switch mounted to the brake pedal. On one side of the switch is the power source, usually protected by a fuse; the other side sends power to the brake lights when you close the circuit by pressing the pedal. 

On many vehicles built within the last decade or so, the brake light switch circuit connects to the body control module (BCM). When the switch is closed, the BCM receives the information and turns on the brake lights. It also shares the switch status with your car’s other computer modules.

» MORE: What to do if your car shakes when braking

Why your brake lights aren’t working

If your brake lights are out, it’s typically because of one of these reasons:

  • Failed brake light bulbs 
  • Problems with the brake light switch circuit
  • Brake light switch problems

Failed brake light bulb

If only one brake light bulb is failing to light up, the problem is almost always a bad bulb. Although it’s less common, sometimes both bulbs will burn out at once. 

Solution: Replace the brake light bulb or bulbs. On some cars, these are easy to access, but other vehicles may require removal of bolts or the tail light assembly. If you lack the right tools or don’t feel comfortable making this repair, your mechanic can handle it quickly. 

Problems with the brake light circuit

Blown fuse: One of the first things to check is the brake light fuse. If the wire between the two sides (also called the element) is broken, the fuse has failed and power will not be able to get to the brake lights.

Solution: Replace the fuse, then continue to monitor brake light operation. Fuses blow from excessive current, which means there may be an underlying problem that could cause the fuse to blow again.

Bad bulb sockets: Bulb sockets that are corroded or damaged my cause excessive resistance in the brake light circuit. This will prevent the brake lights from working properly.

Solution: You’ll need to get the bulb socket or sockets replaced.

Wiring problems: Disconnects, shorts or excessive resistance in the wiring can keep your brakes from lighting up. Broken wires, loose connections, corrosion and more can cause this kind of problem.

Solution: You’ll want a professional to diagnose the wiring problem. Once the cause is identified, it can be fixed or replaced.

Problems with the BCM: On some vehicles, brake light operation is controlled by the body control module. A problem with the BCM or its circuit can keep your brake lights from working.

Solution: Have an auto technician check that the BCM circuit is intact. If the circuit is good, the mechanic will check to for any technical service bulletins; if there aren’t any, the BCM may need to be replaced.

» MORE: Get a fair estimate for your car repairs

Brake light switch problems

Failed brake light switch: In most systems, a brake light switch that has failed in the open position will prevent the brake lights from turning on. On the other hand, a brake light switch that has failed in the closed position will prevent the brake lights from turning off.

Solution: You’ll need to replace the brake light switch. This can be a straightforward project, but if you’re not familiar with electrical circuits, you should let a professional diagnose and work on it.

Misadjusted brake light switch: Some brake light switches are adjustable. A switch that isn’t adjusted right will prevent proper brake light operation.

Solution: Adjust the brake switch according to the manufacturer’s specifications. Again, if you haven’t worked on this type of circuit, let a mechanic handle it.

Get your brakes checked

Even if your brake lights are fine, your brakes should be inspected at least once a year. How often you need to get them replaced will vary depending on your car and your brake usage.

Remember, brakes are the most important safety feature on your car, and if something seems wrong with them, get your car inspected by a professional technician immediately.

Mia Bevacqua

About the Author

Mia Bevacqua is an automotive expert with ASE Master, L1, L2 and L3 Advanced Level Specialist certification. With 13-plus years of experience in the field, she applies her skills toward writing, consulting and automotive software engineering.