3 Common Reasons Why Your Brake Lights Won’t Turn Off
The importance of the brake light system cannot be overstated. For this reason, understanding how these lights work, how to check their operation and failure modes is beneficial for safe driving.
Sometimes, a malfunction occurs in the brake light system, causing the brake lights to not turn off. Read on to understand the most common causes of this problem and how to fix it yourself.
How Brake Lights Work
Brake (or stop) lights are part of the tail light installation on your car, truck, or SUV. Brake lights were first used on automobiles in 1905.
At the time, drivers used hand signals to inform following vehicles that they were stopping or turning. Hand signals are still in fashion today for cyclists and some motorcyclists, but they have become less popular in automobiles.
As more and more manufacturers began to install brake lights (or lights) on the rear of their cars, in 1928 11 U.S. states mandated that all cars be equipped with such warning lights.
This was a response to the increase in nighttime automobile traffic and the resulting increase in rear-end collisions. It took several years for brake lights to become a legal requirement across the United States.
In 1974, so-called high or third brake lights became mandatory for all cars. These warning lights are located higher, making them more visible to following drivers and reducing the risk of rear-end collisions.
Needless to say, pressing the brake pedal turns on your car’s rear brake lights. This proper function occurs even when the engine is not running and the ignition is turned off. But what does it do?
Most cars have a switch (the brake light switch) under the dashboard on the driver’s side. This switch looks like a push button. That button (or piston) makes contact with part of the brake pedal lever.
When you apply the brakes, this lever moves forward, extending the piston. The piston then activates a switch contact, which sends an electrical signal to your car’s brake light system and turns on the lights. Easy, right?
Older cars made in the US before 2006 used this switch to directly control power to the brake lights. The wiring for those brake lights went directly through this switch, just like your kitchen wall switch or ceiling lights. That was easy. But not today.
Today’s cars use a computerized system called the Controller Area Network (CAN) bus system to control many of the car’s interior systems, including the car’s exterior lighting.
This system reduces the amount of wiring throughout the vehicle and improves control and troubleshooting of systems that use computer control, such as the ECU (Engine Control Unit).
The CAN bus system also controls the brake lights. When you press the brake pedal, a coded signal is sent through this system to a control module. This module sends power to these lights, and the lights come on. A big advantage of this system is that it can detect defective brake bulbs.
If a bulb fails, a warning light or a graphic display will appear on the instrument panel. Not only will you know that the bulb is not working, but if there is a graphic display, it will also show you the location of the broken bulb. In most cars, this error will trigger a diagnostic trouble code (DTC). This code can be read with an OBD2 code reader and will indicate the type of electrical fault that has occurred.
Why Brake Lights Won’t Turn Off (While Driving)
Brake lights won’t turn off while driving
This can happen while you’re driving. The most annoying thing is that you don’t realize they’re on. Here are some reasons for this particular malfunction:
1) Defective brake light switch
The brake light switch is located near the brake pedal connection and may be faulty. Even though it may seem like it’s working fine when you press the pedal, the electrical signal that turns on your brake lights won’t go away.
This is a rare mistake, because car manufacturers design this switch to be very reliable. However, it is possible for it to fail and leave your brake lights on all the time. Replacing the switch is relatively easy if you’re flexible enough; otherwise, go to a repair shop to have it replaced. In some cars, the brake light switch piston contacts a plastic or rubber bumper on the brake pedal lever. This buffer can break, fall off, or break apart. Without a buffer, the switch piston extends and the brake lights come on.
If your brake lights don’t turn off and you find small pieces of plastic (or rubber) in your footwell, this broken buffer may be the problem. See a mechanic for repairs. This issue is common on several Honda, Hyundai and Mazda models.
2) Brakes
This issue is very common. While driving, place your left foot lightly on the brake pedal. Yes, this will prepare you to brake. Not a bad idea. However, be aware that virtually any movement of the pedal even a fraction of an inch will cause your brake lights to come on.
If your car has an automatic transmission and you normally brake with your left foot, be absolutely sure not to put that foot on or even touch the brake pedal.
3) CAN Bus System Malfunction
The CAN bus system can fail. This can be a hardware or software issue and can only be diagnosed and repaired by a qualified mechanic.
