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Sometimes you disengage the park brake and start driving but later notice the light on the dashboard is still on. What causes the brake light to stay on when it should have gone off? If you have no idea, this post is for you. Read on.

There are several lights which could illuminate on your dashboard, all intended to alert you that a certain part of your car’s systems needs attention. The parking brake light could appear as an illuminated ‘P’ or as an exclamation mark. In some cars the light is orange and in others it is red.

When you park your car and pull up the park break (if it is a lever) or step on the park brake pedal to engage it, the light should come on. This confirms that the park break is fully engaged. When you start the car to drive off, you lower the park brake lever or release the pedal to disengage it. The light should automatically go off.

What Causes the Brake Light to Stay On?

Sometimes you disengage the park brake but the light on the dashboard stays on. Why does this happen?

Brake only partially disengaged

You pull out of your parking as usual and get on the road only to realize the brake light is still on. Why is the parking brake light on while driving? The most common reason this happens is because you forgot to disengage the park brake. You may have forgotten to disengage it at all. Sometimes you may have disengaged it hurriedly and failed to push it all the way down. If you forgot to disengage it and you end up driving with it still engaged, it will cause premature wearing of the brake pads and could damage other components of the brake system. If it is disengaged but not fully, there may be no damage to the brake pads only that the car’s sensor reads it as still engaged therefore leaving the light on.

Low Brake Fluid

Another reason your brake light could prove stubborn is if the brake fluid is running low. The reservoir used to store the fluid in the engine has a sensor which causes the light to come on when fluid levels are low. When brake fluid levels seem to drop drastically even after being refilled, there could be a leak in the system.


The system depends on a sensor to tell it if the park brake is engaged or not. It depends on another sensor in the brake fluid reservoir to tell it when fluid levels are low. We can compare these sensors to messengers who report to the authority when something is out of order. Sometimes messengers, for one reason or another, give authorities wrong messages. Similarly, if the sensors in either of these components are faulty, the light still comes on and gives the impression that the park brake is engaged.

Worn brake pads

As brake pads wear out, brake caliper pistons have to extend further to ensure contact between the pads and the rotor is maintained. The extra space is filled with brake fluid. This causes an abnormal drop in brake fluid levels. This drop then makes the system report low brake fluid which makes the brake light come on.

What to Do If the Brake Light Stays On

Trying to find the reason behind a brake light that stays on can be frustrating because it could be caused by any one of a number of reasons. You have to try several solutions and keep checking to see if the light has gone off after each try.

If you notice the park brake light on while driving, stop as soon as it is safe to do so. The first thing you should check is if the park brake is fully disengaged by pushing the lever all the way down. If the light goes off, you know exactly what the problem was and you can be on your way. If it stays on move on to another check.

Next, pop the hood and check the brake fluid reservoir. If the level is very low, fill it up to the appropriate level. Always have some brake fluid in the trunk or glove compartment incase need for a quick refill arises. Turn on the engine and press on the brake pedal several times to let the fluid flow through the system. In the event that the level of fluid drops drastically, you might be dealing with a leak somewhere along its path. Check under the car for a little pool of oil.

Now check the brake pads. With the car stationary, turn the steering wheel either to the left or right and push it as far as it can go. With the wheels turned outward completely, you can get a good look at the brake pads through the wheel. The minimum thickness for brake pads is 1/8 to 3/16 of an inch. Although visual inspection only allows you to make rough estimates, you should be able to tell if the brake pads are a possible cause or eliminate them as a probable cause of the problem. If the mechanic confirms that brake pads were the reason behind the light, he will recommend refilling brake fluid as a secondary remedy and replacement of brake pads as a primary one.

Read codes

If after all this the light is still on, call in a professional mechanic to look at the car. The mechanic should use a scan tool to read fault codes off the car’s inbuilt computer. Once these codes are interpreted, he may be able to identify the problem and fix it.

What Causes Dirty Brake Fluid?

A vehicle’s brake system is closed so technically it should be impossible for brake fluid to get contaminated. How does brake fluid get contaminated? Let’s look at two main ways of contamination and how they happen.

Moisture contamination: Brake fluid is hygroscopic which means that it absorbs moisture from the air. Even if it is not exposed to air, it absorbs moisture through hydraulic lines and gradually becomes contaminated.

Effects of moisture in brake fluid: When the fluid absorbs a significant amount of moisture, it causes chemical breakdown and the metal components of the system begin to rust. The key effect of moisture is that it drops its boiling point so it easily boils when it is exposed to the high temperatures produced by aggressive or frequent braking. This is dangerous because it then causes overheating of all the components which makes them wear out faster or in extreme cases melt out completely.

Brake fluid can be tested to determine if it is contaminated. If it contains more than three and a half percent moisture, it is considered to be contaminated. This threshold is used because this amount of moisture can drop the fluid’s boiling point by up to 100 degrees. Here is a quick comparison: When Dot 3 brake fluid is contaminated for instance, it means its boiling point can drop from 205°C to 105°C. This makes it only 5 degrees better than plain water where boiling point is concerned.

Grime and debris: Dirt could get directly into the reservoir if the mechanic working on your car is not careful to make sure none of the surrounding dirt gets in when it is opened during regular maintenance. Dirt can also come from within the system. Rubber brake lines are made to withstand corrosion from the fluid. Even then, they do eventually deteriorate. Tiny bits of rubber leach out of the lines into the fluid and this also contributes to contamination.

How Often Should Brake Fluid Be Changed?

Auto experts say brake fluid should be changed every 2 years. It is best to check the owner’s manual to get a duration specific to your car. Durations given by these two are based on average operation of the car. These are some instances when you may need to check your brake fluid before the two year mark.

  • Excessive strain on brakes: If you frequently drive on mountainous terrain or tow a trailer for long distances, the demands on your braking system are a lot higher than average. Increased demands mean more moisture is absorbed and will begin to cause problems sooner.
  • Car pulls to one side as you drive: This is a symptom of low brake fluid which is most likely caused by a leak. When you have a leak, it means even the fluid left in the reservoir is contaminated because moisture has seeped in through the gap. This calls for immediate attention from a professional mechanic.
  • Spongy or squishy brake pedal: This is never a good sign. It means there has been a drop in brake fluid level in the reservoir. A spongy pedal has to be pushed down to the floor to get the car to stop. It also calls for immediate attention.

How to Avoid Brake Fluid Contamination

First let’s dispel the notion that you can prevent brake fluid contamination if you are cautious enough. You can’t. It will get contaminated over time no matter what you do to prevent it. Whatever effort you make simply serves to make it last as long as it should.

First, make a point to open the brake fluid reservoir only when it is absolutely necessary. Modern cars have a translucent reservoir for this reason. You don’t have to open it to check the level or the color. This way very little moisture is absorbed from the air. When you do open it to refill or change the brake fluid, do it as fast as you can then replace the cap. Secondly, make sure that the cap is tightly on at all times to avoid moisture seeping in. If the cap is faulty, replace it immediately. These caps are easy to find at just about every auto repair shop and are not pricey.

If your driving habits put abnormally high strain on the brakes, don’t rely on the age of your brake fluid to know when it is time for a change. Instead, have your brake fluid electronically tested annually. This will help you detect signs of contamination before brake performance drops.

Brake Fluid Color

New brake fluid is translucent with a yellow tint to it. With continued use, it darkens to become brown and eventually turns black. This color change is caused by moisture contamination as well as flush boiling. When its boiling point drops, it easily boils when the system produces a lot of heat. Repeated boiling causes gradual darkening.

How to Know If Your Car Needs Brake Pads

The general rule is that brake pads fall due for replacement after about 50,000 miles (8,500km) – some last longer while others thin out after even 25,000 miles (42,500 km.) The owner’s manual should give you a more accurate figure specific to your car, though it all depends on driving habits and several other individual factors. These are some reasons your brake pads may not last as long as they should.

  • Driving Habits: The amount of force used to step on the brake pedal affects the lifespan of the brake pads. If you usually ride the brakes and often stop abruptly, don’t be surprised if your brakes don’t last long. It is recommended that you brake gradually and smoothly whenever possible. Of course some emergency situations call for sudden slamming on the brakes but these are few and far between so they are unlikely to affect lifespan.
  • City and Country driving: If you often drive in the city your brake pads won’t last as long as they could. Stop-and-go traffic and traffic lights in the city are harder on brake pads compared to country or long distance driving. In the latter, braking is required less frequently.
  • Type of brake pads: There are different kinds of brake pads designed for different driving needs. They are made of varying compounds, some suited for performance cars and others for regular city cars. Hard compound brakes used on performance cars are more durable but usually have to warm up before they can perform optimally. Soft compound brakes are made for low speed cars. They are less durable and cannot withstand high temperatures.

What Do Worn Brake Pads Feel Like?

It is almost impossible for your brake pads to get badly worn out before you notice a few changes in the car. It is important to know the classic symptoms of bad brake pads so you won’t wonder what’s going on. Here is what to look out for.

  • Reduced braking power: When brake pads are extremely worn, they cannot provide enough friction to slow down the rotor quickly. Although the car eventually stops, it takes a lot longer than it ordinarily would to stop.
  • A squealing noise from the brakes: Unlike other unpleasant noises caused by the brakes, this one seems to be heard when you get your foot off the brake pedal. Most brake pads today are made with built-in wear indicators. When they start getting worn out and you hear the squeal, the indicators are just doing their job. Wear indicators are metal tabs near the top of the pads. When the pad is worn out the indicator scrapes on the rotor.
  • Pulsating or shuddering: Pulsating or shuddering felt on the brake pedal and/or the steering wheel when braking is a classic sign that all is not well in the braking system. This is also a sign associated with warped rotors so when you experience this, it probably means that you need to replace both brake pads and rotors.
  • Spongy Brake pedal: When you step on the brake pedal it feels squishy. You will still be able to use the brakes to stop but will have to press down hard on the pedal to get the car to slow down and stop. This is dangerous because you may forget that the pedal needs more pressure than usual when you need to make an emergency stop.

How to Tell If You Need New Brake Rotors

After paying so much attention to brake pads, don’t forget to check your rotors. After all, even the best brake pads in the world cannot work well with a faulty rotor. The rotor should be smooth with a perfectly even surface. This way brake pads can grip it easily and bring the car to a smooth stop. How can you tell when it is time to change brake rotors?

  • Wobbly braking: If you feel a strange wobble in the car every time you hit the brakes, the rotor is probably warped. Rotors often get warped due to excessive heat produced during frequent, aggressive braking. The wobble happens because the brake pads cannot achieve a perfect grip on the rotor as it spins.
  • Thinned rotors: When rotors develop grooves and heat spots, their lifespan can be extended by resurfacing them. This process thins the rotor so it is important to measure the thickness of your rotors to make sure they never get below the minimum allowable thickness. When they do, you have no choice but to replace them.
  • Grinding or growling sound: If you continue to drive on worn brake pads, they get completely worn out and the metal on which they were attached is left exposed. The growling sound is produced when this metal comes into contact with the rotor. If it doesn’t go on for long, the damage on the rotor may be minimal. If it the two metals rub against each other for long, this will destroy the rotor, necessitating replacement.

Why Do My Brake Lights Stay On When My Headlights Are On?

The very first headlights used on vehicles were acetylene based flames. These had to be lit manually by the driver and did not last very long. Today, more than a hundred years later, modern cars have high and low beam headlights which are toggled on and off from inside the car. The switch is connected to the battery which is the source of power for all lights, including brake lights.

Sometimes you may find that your brake lights come on when you switch on your headlights. The brake lights remain on as long as the headlights are on, whether or not you step on the brake pedal. This happens when wires linking the brake lights and those linking the headlights to the battery come into contact and rub against each other. Although wires are covered with an insulating coat, rubbing together could make the insulating coat wear off and expose the internal parts of the wires. This exposes the two sets of wiring to each other electrically and creates a common electrical connection. Switching one on automatically switches on the other.


Out of all the subsystems which come together to ensure smooth running and operation of your car, the brake system is one you can never afford to ignore. It may be annoying when you have to go through step after step to trying to figure out why the brake light is on, but with brakes, you really have no choice. What causes the brake light to stay on? First check that you haven’t forgotten to disengage the park brake and then make sure the brake fluid is sufficient. These are the two main reasons the light could stay on.


Where is the brake light switch located?

The main purpose of this switch is to supply power to the signal lights anytime you press the brake pedal. You can locate the brake light switch by checking for it under the dashboard. Most of the time the brake light switch will just fail without notice and a driver behind you will have to inform you that your brakes lights are not working. Generally the brake light switch will cost you around $30 to $75 depending on type and make of car. One of the key symptoms of a faulty brake light switch is your brake lights remain on at all times even when you are not engaging the braking pedal.

What happens if my brake lights do not come on?

Whenever you encounter such a situation, the first step is to check whether the third brake is functioning. If it is not then the problem could be unplugged harness, faulty brake light switch or a bad fuse. If your car comes with emergency flashers you can use them to test your brake lights. If the emergency flashers come on then know that the wiring is still good as they use the same as the main brake lights. If they fail then the problem is the fuse.

What does the law say about faulty brake lights?

Brakes are critical to inform the person behind you that you are slowing down your car. In the absence of the braking lights you can come hitting someone from behind at high speeds. According to federal law, all cars should be fitted with a third brake light. It also adds that this third brake light should be similar to the other brake lights. A cop can pull you down if you do not have this third brake light and in most cases you will not pass the state inspection.

Does Brake Fluid Evaporate?

Brake fluid is contained in an air tight reservoir so it is unlikely that it would evaporate. If the levels of brake fluid in your car are dropping at an alarming rate, it could be because your brake pads are worn. When you step on the brake pedal, the caliper piston has to move out further. It is gradually pushed out of its housing in order for the pads to come into contact with the rotor. The extra space created is filed with brake fluid. This is why fluid levels in the reservoir appear to drop significantly over a short time. It is filling up the braking system.