Brake Lamp Bulb Fault (Causes & Fixes)
Updated: Feb 1
✔ This article has been fact checked.
A brake lamp bulb fault can occasionally occur on your vehicle, if this happens your brake lights will not turn on in response in you pressing on the brake pedal. This issue can be very dangerous if left unfixed.
There are many causes of a brake lamp bulb fault. Blown bulbs, faulty brake light switch, damaged or loose wiring, blown fuses, and malfunctioning relays and modules can all cause this fault.
It's most commonly a blown bulb or fuse that causes this issue, but it can be any number of things.
Table of Contents:
What Does It Mean?
Some vehicles have a built in system for detecting blown bulbs and issues with exterior lights, this can cause a warning light or "brake lamp bulb fault" message to appear on your dashboard.
In general, this warning refers to the brake pedal not illuminating the brake lights. Not all vehicles will see this warning message, and it does not always occur.
This alert that appears on some cars is only a warning and you should visually check all exterior lights to see if they're working properly.
Causes of a Brake Lamp Bulb Fault
There are a multitude of possible causes for a brake light fault, including the following.
1. Blown Bulbs
Brake light bulbs, as well as most other bulbs, don't last the life of the vehicle. They will ultimately stop illuminating since they deteriorate with age, lose their brightness, and eventually stop working completely.
The brake lamp bulb may flicker or not illuminate at all due to a blown bulb.
Some brake light bulbs last a lot longer than others, halogen bulbs typically last the shortest amount of time and LED bulbs will last the longest.
Note that some cars may throw a CANbus error if you replace a halogen bulb with an LED equivalent.
2. Faulty Brake Light Switch
Only when the driver hits the brake pedal do the brake lights illuminate. When you press the brake pedal, a brake switch activates the brake light lights.
This switch is located by the pedals. Sometimes it may be electronically controlled by a brake pedal position sensor, in which case this would be the issue.
A faulty brake light switch is another common cause of this issue.
3. Damaged or Loose Wiring
Sometimes the issue may damaged or loose wiring, it could be caused by an animal chewing through wires, corrosion, vibration causing a wire to be damaged or it could be a connector that has come loose.
You could check all the brake lights for any wiring issues, or it could be the wiring related to the brake light switch, fuses and relays, etc.
Any damage to the wining or connection that has come loose can result in a brake lamp fault, it may also cause flickering of a bulb.
4. Blown Fuses
Fuses protect components from electrical surge and prevent too much power going to them.
The majority of fuses have two terminals, and these terminals are connected by a thin piece of metal. It will not send electricity to the primary component it is protecting if the metal strip breaks or the fuse burns.
When a fuse to a brake light bulb, brake pedal position sensor, or brake switch, blows you will likely encounter a brake lamp fault.
Sometimes a blown fuse can cause the brake light to flicker or not work completely.
5. Malfunctioning Relays and Modules
Relays and modules are used in the wiring of a brake light system, if they fail they can cause a brake to fail too.
Fixing a Brake Light Fault
Fixing a brake lamp fault depends on what caused the issue in the first place.
Check the bulbs first, if they are fine you should check the wiring for damage and loose connections, if that's not the issue it could be a blown fuse, a defective relay or module, or a faulty brake switch.
Replace the Blown Brake Light Bulbs
If a blown brake light bulb is the culprit, changing the bulb is easy.
The brake light assembly should be removed, it's usually held in place with screws, bolts or clips.
Examine the bulb's connection after carefully unplugging it. If the bulb contains a dust-like material, the filament has fractured or has gone dark brown; you need to replace the bulb.
Purchase a new bulb, then replace it, the mechanism holding in a bulb can be different depending on the car brand.
Replace a Faulty Brake Switch
If a faulty switch is to blame, you need to replace the switch. The brake switch is usually located near the pedals. Find the dead switch, then swap it out with a working one.
Some vehicles may use integrated pedal position sensors so this issue could be more complicated depending on the manufacturer.
Repair Damaged or Loose Wiring
If the issue was damaged wiring you should replace the section of wire that is damaged, if it cannot be replaced you should solder or crimp the wires back together or use a connector block, make sure you waterproof it and wrap it tightly with electrical tape.
Loose wiring should be reconnected and properly secured.
Replace Blown Fuses
If the issue was a blown fuse you should replace the blown fuse with a new one of the same amperage. Do not use a higher or lower rated fuse, use the same as the one which you are replacing.
For example; if the blown fuse is 5A, use a 5A rated fuse and not a 10A fuse.
Turn the engine off and look for the fuse box (its usually located in the engine bay somewhere, its different for every vehicle).
Follow the directions on the fuse cover or vehicle manual to find the brake light fuse. A fractured metal strip will span the two terminals of a bad fuse.
Remove the old fuse and test it using a fuse remover and tester kit.
If the fuse is blown replace it with a fuse of the same amperage rating.
Can You Drive if One Brake Light Is Out?
It is generally not safe to drive a vehicle with any of its brake lights not functioning. Brake lights are an important safety feature on a vehicle, as they alert other drivers when you are slowing down or stopping.
If one of your brake lights is not working, it could be difficult for other drivers to react in time when you are braking, which could lead to a collision.
In most places, it is also illegal to drive a vehicle with a faulty brake light. If you are pulled over by a police officer and found to have a brake light that is not functioning, you could be issued a fine or ticket.
It is usually best to have any faulty brake lights repaired as soon as possible to avoid any potential issues while driving.
How Much Does It Cost to Replace a Brake Light Bulb?
Fixing a brake lamp bulb fault doesn't usually cost a lot (usually around $30 / £25 but the price can vary) if its simply a blown fuse or brake light bulb.
However, if its a brake switch, pedal position sensor, damaged wiring, or another issue it could potentially cost a lot more.