Brake Lights Won’t Turn Off?
The importance of the brake light system cannot be overemphasized. For this reason, understanding how these lights work, how to check their operation and failure modes is beneficial for safe driving.
Sometimes, the brake light system can fail and the brake lights won’t go off. Read on to understand the most common causes of this problem and how to fix it yourself. Here’s how brake lights work
Brake lights (or stop lights) are part of the tail lights on cars, trucks, and SUVs. Brake lights first appeared on cars around 1905.
At the time, drivers used hand signals to indicate to following traffic that they were stopping or turning. Hand signals are still popular among cyclists and some motorcyclists, but are rare in automobiles.
Many manufacturers began installing brake lights (or lights) on the rear of their cars, so in 1928 11 US states mandated that all cars have such warning lights. This was a response to the increase in nighttime car traffic and the resulting increase in rear-end collisions. It took several years before brake lights became a legal requirement across the United States.
In 1974, the so-called high or third brake lights became mandatory for all cars. The elevated position of these warning lights improved visibility to following drivers, further reducing the risk of rear-end collisions.
Needless to say, pressing the brake pedal turns on the car’s rear brake lights. This proper functioning occurs even when the engine is not running and the ignition is off. But how is this accomplished?
Most cars have a switch (the brake light switch) under the dash on the driver’s side. This switch resembles a push button. That button (or piston) makes contact with a portion of the brake pedal lever. When you apply the brakes, this lever moves forward, extending a piston. The piston in turn 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 the wall switches in your kitchen or the lights in your ceiling. That was easy. But today, not so much.
Today’s cars use a computerized system called the Controller Area Network (CAN) bus system to control many of the interior systems, including the car’s exterior lights.
This system reduces the amount of wiring throughout the car 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 they come on. A big advantage of this system is that it can detect defective brake bulbs.
If a bulb fails, a warning light or graphic display appears on the instrument panel. Not only will you know that the bulb is not working, but the graphic display (if available) may also show the location of the broken bulb.
In most cars, this error will trigger a Diagnostic Trouble Code (DTC), which can be read with an OBD2 code reader and will provide information about the type of electrical fault that has occurred.
