Brake Pedal goes to Floor when Engine Running

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A really scary image comes to mind whenever my brakes pedal goes to the floor when my car is running. It means that I am about to lose my brakes and hit something or someone. Obviously, anyone who owns or drives a vehicle hates the feeling of losing brakes. A car without working brakes is not safe to operate on road, so finding out what’s wrong with your vehicle’s braking system is quite crucial.

Now the trick is being able to find out what is the culprit and identifying it in time before you hit something or someone. Lucky for us, there are great number of ways we can determine and find what’s wrong and our break components need repair. 

So, in this article, we are going to look into some of the most common reasons why the brake pedal goes to the floor.

What Causes Brake Pedal Go to Floor When Engine Running?

Here are some common causes of the brake pedal going to the floor.

Loss of the Brake Fluid

Brake fluid operates the master cylinder, which in turn actuates the hydraulic piston so as to push fluid down to all your brake’s calipers. When the braking system starts leaking, you will start seeing some major changes on your vehicle. The Brake pedal goes to the floor once it starts getting harder to press and slower return.

Bad Brake Master Cylinder

Under normal circumstances, the brake pedal should go up and down with equal force once the Brake Master Cylinder is doing its job. However, if your car’s brake master cylinder starts failing to work properly, it will start leaking. The brake pedal will go all the way down to floor level due to a loss of fluid pressure.

Bad Brake Booster

The brake booster’s role is to ease the pedal for braking. A worn brake booster can fail to do its job of easing down on the brake pedal and thus making it go all the way down to floor level. A faulty valve in the brake booster can restrict the flow of fluid through it, causing a reduced amount of pressure on the brake pedal.

A brake booster comprises of a mechanical linkage that includes parts like the vacuum hose, lever arms and pivots. Any faulty in this system will affect pressure on your car’s braking system.

Presence of Air in Brake Lines

After a new master cylinder replacement, air might find its way into your brake lines and cause the brake pedal to go all the way down. Fluid cannot enter the master cylinder if air is present in the line, so it causes a loss of fluid pressure and causes low braking system’s performance on your car.

A faulty brake booster can also be caused by air entering through seals as such does not allow for proper tightness around the master cylinder pushrod area due to swelling of rubber over time. If you suspect some air bubbles might have gotten into your Master Cylinder reservoir or brake booster, you should bleed the brakes immediately to get rid of any air that might be trapped and causing problems with your car’s braking system.

How to Fix Brake Pedal Going to the Ground When Engine Is Running

So here comes the most exciting part. If you have done all the mentioned checks above and it’s confirmed that your vehicle brakes are not working, then your braking system needs some repairs.

Look for external leaks

Inspect the braking system for any external leaks. The brake fluid will leak out through small openings and look like dampness on your car’s carpet, seats or floor. If you find any of these signs, then there is a high possibility that you have a leaking brake line somewhere in your vehicle.

Check brake fluid level

Another simple fix is to check your brake fluid level as getting it low on the reservoir might cause for very poor brake performance. Low brake fluid level will not let you push on the pedal which causes it to go all the way down and hit the floor. Open up the brake fluid cap and if your brake fluid level is low, then you need to add some through the reservoir.

Bleed the brake system

In this method, you need to re-establish the smooth flow of fluid through your braking system. You can do this by bleeding and compressing the brake lines and push the pedal according to the instructions given in your vehicle’s manual. For this you may need a helper.

After bleeding the brake system, check whether your brakes are working as expected or not. If the problem is still there, then you might have a problem with the internal parts of your braking system.

Disconnect the brake booster’s vacuum hose

Doing this will disconnect the brake booster from the fluid pressure of your vehicle’s braking system. This way you can check whether the problem is with the Brake Booster or not. If there is no change in your brake pedal height, then that means that your booster is fine, but you might have air trapped inside it.

In some cases, the hose might be the cause of brake pedal going to the floor and you can check by removing it and see if that works.

Check or Replace master brake cylinder

If all the above checks are not helping you out with your braking system, then there is a problem with the master cylinder. This brake component is fitted in the car’s transmission and pushes the hydraulic fluid through the car’s braking system. It can leak or get damaged if mishandled so check for any visible signs of damage on it.

Inspect or Replace Brake Booster

Another culprit of brake pedal going to the floor is your brake booster. You can check it and see if it’s defective or not by checking for any leaks and damage on it. The brake booster is a small canister that you can see near the brake master cylinder.

Frequently Asked Questions

Why does my brake pedal sink when I start my car?

The majority of brake pedal sink issues are caused by the master cylinder, a brake fluid leak, or an ABS unit leak.

How do I know if my brake booster has a vacuum leak?

Leaks in the brake booster are responsible for a vacuum leak. They are common in older brake boosters.


In conclusion, the brake pedal goes to the floor because of faulty brakes. Faulty brakes are usually caused by air bubbles in your reservoir or brake booster, low fluid level, damaged master cylinder, defective brakes (brake pads and brake shoes), failed ABS system etc. This is why it’s important to do regular car maintenance so you don’t have to go through this issue again.

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