Having a functional brake system in your car is essential for safety reasons. A faulty brake pedal not only puts your life in danger, but it also puts the lives of other people at risk. However, many people often overlook the brake pedal until it completely deteriorates and stops working.

Normally, a brake pedal shouldn’t go all the way down. If it does, it means there’s something wrong with it. Do not wait until it stops working completely before you have a professional mechanic look at it.

In this article, we will look at factors that cause the brake pedal to go all the way down while the engine is running. Stick around to find out more about these factors.

What Causes Brake Pedal Goes to Floor When Engine is Running?

If your brake pedal goes to floor while the engine is running, several factors could have led to that. These factors include the following:

Bad Brake Master Cylinder

One of the major factors that cause a brake pedal to go to the floor is a bad brake master cylinder. The master cylinder is responsible for compressing brake fluid. The pressure on the fluid allows the brake to hold the front and rear wheels whenever the brake pedal is applied. That is why the master cylinder must be properly sealed to prevent internal leaking.
A faulty cylinder with a broken or worn-out rubber seal will make you lose braking power. That is because it lacks the needed pressure, due to internal leaking. Hence, the reason it goes all the way down. At this point, you won’t feel the firmness of the brake pedal anymore when you depress it.

Loss of The Brake Fluid

Another factor that causes no brake pressure when car is running is the loss of brake fluid. Brake fluid helps in sustaining your car’s braking power. When your car is running low on brake fluid, the brake pedal won’t be as effective as before due to loss of pressure. You may need to push it all the way down before it responds accordingly. At this point, the deceleration rate of the car will be very slow.

Bad Brake Booster

If you have a situation where the brakes go all the way to the floor but still works, then you may be having a bad brake booster. The brake booster which is often referred to as the power booster provides power assistance to the braking system so that you don’t have to fully depress the pedal all the way down before the car comes to a stop. In other words, it enables fast deceleration.
The brake booster can be found in between the brake pedal and master cylinder. When you have a faulty power booster, you’ll notice an increase in the stopping distance. You will need to fully depress the pedal down to the floor before the car comes to a complete stop.

Presence of Air in Brake Lines

Does your brake pedal goes to floor after replacing the master cylinder? If yes, then there’s a presence of air in the brake lines. Many car owners often wonder why the brake pedal of their car goes to floor after changing the master cylinder. This happens when no air bleeding is done after replacing the master cylinder.
After replacing your master cylinder with a new one, you need to make that the mechanic bleeds the air out. If this isn’t done, there may be air in the brake lines that could disrupt the flow of brake fluid. This can lead to the total damage of the brake lines. Once that happens, the brake pedal starts going to the floor whenever you depress it.

Brake Fluid Leak

Another common cause of loss of brake pressure is brake fluid leak. This usually happens when one of your brake lines is leaking. Brake fluid leaks are very easy to diagnose. If you have a brake fluid leak, there will be a yellow, brown, or colorless fluid on the floor where your car was parked overnight.

Basic operation of braking system: image
Basic operation of braking system

How Do You Fix Brake Pedal Goes to Floor When Engine Running

Now that you know what causes brake pedals to go to the floor, the next thing we will look at is the ways to fix this problem. If your brakes don’t work or not working efficiently, it is very easy to spot and diagnose. You need to understand that this issue doesn’t affect the whole braking system, making it easy to fix. There are several ways you can resolve this problem.

Check Brake Master Cylinder

As previously mentioned, a bad brake master cylinder is one of the major causes of brake pedal issues. A brake master cylinder normally comes with seals that allow it to keep the oil within. However, with time, these seals may begin to wear, leading to leakage of the brake fluid.
The best solution to this problem is to replace the brake master cylinder with a brand new one. Try not to install a used or rebuilt cylinder. A used brake master cylinder may appear to work well initially but it will quickly get weak. Installing a brand new brake cylinder will save you a lot of trouble and expenses.

Brake Lines, Brake Calipers Check

The first thing that comes to many people’s minds when their brake pedal goes to floor sometimes intermittently is the brake lines. If that is the case, the first thing you need to do is check the level of the brake fluid. If it is still full, that means there are no leakages. On the other hand, if the fluid level is low or almost empty, then there is a leakage somewhere.
If you notice that there is a leak, check the four wheels to see if any have oil residue on them. After you do that, check for holes or punctures on the brake lines. When you eventually find the leak, replace the defective part, and refill the brake fluid.
Some of the common questions you will hear many people ask about bad brake pedals include the following:

Frequently Asked Questions (FAQs):

Why Does my Brake Pedal go to The Floor After Bleeding?

If after bleeding the brake you notice that your brakes go all the way to the floor, you need to rebleed your system completely. There’s probably air in it. For best results, use a power bleeder that befits the master cylinder.

Why Do I Lose Brake Pressure When I Start my Car?

If you notice that your brake pedal losses pressure when you start your car, this could be a result of leakages. Having leaks in your braking system could cause this. However, if there is no leakage and the pedal still loses pressure when you start your car, the problem may be from the brake booster.

How Do I Know if my Brake Booster or Master Cylinder is Bad?

Are you suspecting that your master cylinder or brake booster has gone bad? There are several ways you can know if your master cylinder or brake booster is bad. Some of these ways include the following:

  • Leaking brake fluid
  • Warning light on the dashboard
  • Hard brakes or lack of brake pressure
  • Sinking brake pedal
  • Engine stalling or misfire when the brake is depressed

What Causes a Hard Brake Pedal?

Several factors could cause a hard brake pedal. A major cause of this is the lack of vacuum pressure. Other factors that could cause a hard brake pedal are as follows:

  • When the brake fluid needs to be replaced
  • When there is a caliper problem
  • When the brake pads are completely worn-out

How Do I Know The Quality of a Brake Fluid?

It’s always best to use a brake fluid that is of high quality. Quality brake fluids will help prevent brake failure and give a better performance. You can easily measure the quality of brake fluids by using brake fluid testers.


If your brake pedal doesn’t work efficiently, as it used to, you need to pay attention to it. Do not wait until it stops working completely. Find a professional auto repair shop that can help you diagnose and fix the problem as soon as possible. This is very important as it will prevent you and other road users from danger.

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