Your vehicle’s lights are more than mere guides to help you navigate under low-visibility conditions一they also help you communicate with other drivers.
But like other components in your vehicle, they can fail or malfunction. Aside from getting burnt out, these lights can also stay illuminated even when they’re not supposed to. Brake lights are susceptible to this kind of issue.
Why Won’t My Brake Lights Turn Off?
There are several reasons why your brake lights won’t turn off even after you’ve taken your foot off the pedal. Here are some of them.
Malfunctioning Brake Light Switch or Sensor
The brake light switch activates the brake lights as soon as you step on the pedal.
In some vehicles, the same switch operates the push-button start and gear selector shift. It can also affect anti-lock braking system (ABS) operation, vehicle stability control, and brake shift interlock.
A problem with the brake light switch or sensor can cause the brake lights to stay on and confuse other drivers because the lights indicate that you’re about to slow down (even when you’re not).
Examples on Fords and Some Asian Makes
The switch or sensor can be misadjusted if it has an adjustment, and many of them do. But on older Fords, the switch is mounted on the pin where the master cylinder pushrod connects to the brake pedal so that the pushrod has to be disconnected from the brake pedal to replace the switch. Those aren’t adjustable, and there are other non-adjustable switches.
On many platforms, the switch interacts with a flat tab. Sometimes, the switch is mounted on the brake pedal and the tab is stationary. Other times, the tab is on the pedal and the switch is stationary. On some Asian makes, there will be a rubber stopper popped into a hole in the flat tab, and if that stopper deteriorates and falls out (it happens), your brake lights will be on all the time and you’ll need to get a replacement rubber piece from the dealer or find some other solution.
Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.
Pro Tip: If the brake lights are operated by a switch interacting with a module, a scan tool can be connected to determine whether the module is receiving a command from the switch. If the switch command changes when the brake pedal is applied and released, but the brake lights are still on, the problem isn’t the switch.
A brake light that’s on all the time can also cause the bulb to burn out faster than normal and might even drain your vehicle’s battery. Note, however, that most modern vehicles have battery saver features and some vehicles are wired so that the brake lights won’t work unless the key is in the on position.
If the brake lights are operated by a switch interacting with a module, a scan tool can be connected to determine whether the module is receiving a command from the switch. If the switch command changes when the brake pedal is applied and released, but the brake lights are still on, the problem isn’t the switch.
–Richard McCuistian, ASE Certified Master Automobile Technician
Stuck Brake Pedal
A stuck brake pedal can keep the brake light switch activated and might even be a safety hazard while you’re on the road.
If you feel like you’re exerting more effort than usual to get your vehicle to slow down, you might be dealing with something more alarming than a set of brake lights that won’t turn off.
A defective brake booster is the most common cause of a stiff brake pedal. Brake boosters, also known as power brakes, use hydraulic fluid to multiply the applied force on the brake pedal.
Most brake boosters are vacuum-assisted, so when the power brakes can’t maintain vacuum pressure, they can’t supply enough power to the master cylinder.
There are other reasons why the brake pedal could get stuck, including a faulty vacuum or power steering pump, cracked vacuum hose, seized caliper, or sludge in the brake lines.
Faulty Brake Pedal Spring
The brake pedal return spring is what causes the pedal to come back up after releasing it.
Together with the brake booster, the return spring helps your vehicle deliver a safe and responsive braking performance.
You might be dealing with a defective return spring if you’re manually lifting the pedal back to its original position. And because the pedal is stuck, you’ll be left with a set of brake lights that are always on.
A faulty brake pedal spring can also keep the brake pads engaged, leading to premature wear.
Electrical Faults
A failing electrical system can cause your vehicle’s lights to malfunction, including the brake lights. But since we’re talking about the brake lights staying on, a malfunction that would cause this problem will typically be directly related to the brake light wiring. For example, if the brake light power wires are shorted to power in a module or in the harness, the brake lights might stay on all the time.
How Do Brake Lights Work?
Brake lights use the high-intensity filament of a double-filament bulb. Meanwhile, the tail lights use the same bulb’s low-intensity filament.
As the driver steps on the brake pedal, the brake switch closes, illuminating the brake lights. The brake light switch receives a hot current from the fuse and is normally open (N.O.) unless the driver depresses the brake pedal. On many vehicles built since 2000, the brake light switch simply signals an electronic module to turn on the brake lights.
Most vehicles manufactured from 1986 up to this day have a third brake light, also referred to as the center high-mounted stop light (CHMSL).
Most brake lights have light-emitting diode (LED) bulbs for two reasons: faster illumination and longer service life.
LED bulbs light up to 200 milliseconds faster than an incandescent bulb, resulting in a greater stopping distance for the driver following the vehicle with LED brake lights. They’re also less susceptible to vibration and will often last as long as the vehicle’s service life.
Stop Light Switch Wiring
Many vehicles over the past 20 or so years have been wired so that the stop light switch simply sends a signal to one of the modules, like the BCM on most cars or the general electronic module (GEM) if it’s a Ford.
The switch can malfunction even on one of these systems and cause the brake lights to stay on. When you have “middleman” modules taking requests and doing the work of turning on the lights, the module can be at fault as well.
For example, on a mid-2000s Mustang, the GEM module can fail internally and light up one or more segments of a brake light so that they stay on all the time. This happens because each segment of those Mustang tail lamps is powered through a different wire from the GEM module, even if the car doesn’t have sequential turn signals.
Brake Light Inspection
Checking the condition of your lights should be a routine task. To inspect the condition of your brake lights, back up close to a wall and step on the brake pedal. You should notice a red glow reflected on the wall behind you.
You can also ask someone to step on the brake pedal while you go around your vehicle and check whether or not both brake lights are working.
Brake Light Service Life
Brake light bulbs can last anywhere between 250 and 650 hours. However, some bulbs can last anywhere from 1250 to 2000 hours. It’s not uncommon for brake lights and other lights to last the life of the vehicle, even if the vehicle has over 200,000 miles.
Brake Light Replacement
Leaving a continuously illuminated brake light unaddressed can significantly reduce its service life and cause it to burn out shortly.
Brake light replacements can cost anywhere between $5 and $10, depending on your vehicle’s specifications (year, make, and model). You can expect to pay another $10 to $20 to have a mechanic replace your worn-out bulbs.
Replacing a worn-out bulb is generally considered a DIY-friendly task. But if you’re not used to doing repairs like this one, you can always take your vehicle to the nearest auto repair shop to have a professional do the job for you.
Wrapping Up
A faulty brake light switch, a stuck brake pedal or return spring, module issues, and electrical faults are some of the reasons why your brake lights won’t turn off. Illuminated brake lights won’t affect your vehicle’s drivability, but they can confuse other drivers and drain your battery.
Also, keep in mind that some causes of an illuminated brake light can also indicate underlying problems with the braking system.
For example, a stuck brake pedal can also mean that something’s wrong with the power brakes. Driving with this issue can put you at risk of getting into an accident because your vehicle won’t have enough stopping power.
So while an illuminated brake light might not seem like a big deal, it’s always a good idea to have it checked right away.
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