Brake Pedal Goes to Floor When Engine Running – Is This Normal or Not?

One of the worst moments ever is when you press the brake pedal and find that the brake pedal goes to the floor when the engine is running at high speed. This situation is not only bad but also very dangerous. People are discouraged from driving a car without the brakes working effectively.

If you ever realize that the brakes have started to weaken or have any strange sound, ensure the vehicle is checked as soon as possible. In this article, we shall know why we can have a spongy brake pedal when the engine is running and how to fix it to have full-power brakes.

Brake Pedal Goes to Floor When Engine Running

What Causes Brake Pedal Goes to Floor When Engine Running

1. Loss of the Brake Fluid

Brake fluid is a very important factor in increasing or sustaining a high brake power. As the driver depresses the brake pedal, the pedal compresses the piston in the brake cylinder. This compression increases pressure in the brake lines, making the brake fluid particles move to the brake caliper. Due to the brake fluid’s high pressure, the brake pads move and squeeze into the brake rotor.

Read Also: Brake Caliper Sticking When Hot [Causes and How to Fix it]

This results in friction, which makes the car stop. So, what happens if there is a brake fluid leakage in the brake lines? In this case, there won’t be any pressure on the brake pedal. Therefore, the brake pedal goes to the floor suddenly, and the car won’t stop or will make a very slight deceleration.

2. Bad Brake Master Cylinder

In normal circumstances, the brake pedal push should feel firm under your leg since it is connected to the master cylinder with a push rod. The master cylinder generates hydraulic pressure to activate brakes and pushes the brake fluid to the front and rear wheels.

Read Also: No Brake Fluid Coming Out When Bleeding [Causes and Fixes]

The master cylinder must be sealed to keep pressure and power, which pushes the brake fluid to the calipers. Therefore, if the rubber seals that keep the brake fluid inside are worn out or get torn, it will lead to internal leaking, which finally causes the spongy feel under your leg.

3. Bad Brake Booster

If the brake pedal goes to the floor but still stops, you could be having a failed brake power booster. The power booster’s role in the braking process is to give power assistance when the driver depresses the pedal. This means that you don’t have to make a very high amount of power to stop the car. The brake booster is situated between the master cylinder and brake pedal and connected to the engine.

It uses a vacuum line to overcome fluid pressure in the braking system. When the brake booster is faulty, you will feel that the stopping distance is increased. The pedal goes all the way to the floor to stop the car completely. This happens because you are not getting the sufficient power boost required to stop the car.

4. Presence of Air in Brake Lines

Many drivers have reported that the brake pedal goes to the floor after the new master cylinder replacement. This happens mainly if no air bleeding is done after installing a new master cylinder, and thus, there is air in the brake lines. The air prevents brake fluid from efficiently flowing inside the brake lines, damaging the brake lines and giving the feeling of a spongy soft feel instead of the firm feel of the brake pedal when depressing.

Read Also: Top 10 Best Brake Line Benders Reviews

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

Although having your brake pedal go to the floor when the engine is running is bad and dangerous, it is very noticeable and easy to diagnose. This fault does not involve many parts of the braking system. To fix this problem, start diagnosing the fault well:

brake pedal hard when car is off then soft when the car is on

Brake Lines, Brake Calipers Check: The first thought that comes to anyone’s mind when the brake pedal goes to the floor when the engine is running is that there is a leakage in any of the brake lines that outflows the pressure in the brake system. The first thing you require is to check the brake fluid level. If it is full capacity, then there is no leak. If otherwise, you have a leakage somewhere.

In case there is leakage, make an eye check on the four wheels to see if there is any oil residue on one of them. Then, check the brake fluid lines themselves to see if one of them has a hole or something. Finalize by replacing the defective part and topping up the brake fluid level.

Check Brake Master Cylinder: The next check to perform is the brake master cylinder since it has some seals to close the oil inside. As we stated in the previous section, these seals may wear with time due to the car’s age, causing brake fluid to leak. In this case, the master cylinder should be replaced with a new one.

Try not to install a brand-new one and not a rebuilt one. A used cylinder will not last long. It may work well for a start but get weaker over time.

Brake Pedal Goes to Floor When Engine Running


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

You can lose brake pressure after starting your car if you have a leakage in any of the brake components. If the brake pedal goes to the floor but has no leaks, the problem might be related to the brake booster that has a vacuum leakage.

How Do I Know If My Brake Booster or Master Cylinder Is Bad?

There are many ways to identify a bad master cylinder or brake booster. You can feel the brakes are so spongy or very soft under your leg, or there is a leakage in the master cylinder. You can also feel that the brake pedal is hard to press or the engine is stalling and stop working while braking. All these are signs of a bad brake booster or master cylinder.

Why Does My Brake Pedal Go To The Floor After Bleeding?

After bleeding the air out of the brake fluid, you must make some hard pressings on the brakes to retain the pressure back to the brake lines.

Should Brakes Be Bled With the Engine Running?

Brake bleeding should be performed while the engine is shut off. Learn More By watching YouTube Video:

What Causes a Hard Brake Pedal?

A hard brake pedal always means that the brake booster has a problem. The brake booster use vacuum air from the engine to assist in pressing by providing pressure to the brake master cylinder.

Final Words:

The best approach for resolving this problem is to have a correct diagnosis. If you find yourself confused about the fault, take the vehicle to an expert for inspection. Remember that any fault related to the brakes is related to the vehicle’s safety and the people who use it; thus, repairs must be done right. To maintain your vehicle’s brake system in good condition, change the brake fluid at certain intervals.

Learn More:


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

2 thoughts on “Brake Pedal Goes to Floor When Engine Running – Is This Normal or Not?

  1. Hi
    If you applied enough pressure on the pedal while bleeding, there’s a possibility that there’s air leakage between the master cylinder and the brake savor.

    To check if there’s air between the brake savor and the master cylinder, pour water in a container and add a little detergent and spray it, if it’s foaming it’s an indication that there’s a leakage of air.

    To fix this, apply a sealant on the savor before fixing the master cylinder.

    And if it’s not leaking, try to adjust the push rod that connects brake savor to brake pedal.

  2. Hi, I have a corrola vvti, recently changed master cylinder and break booster, bleeded the breaks nicely, but still the break pedal is going to the floor. Leaks inspected but, the problem is still there.

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