Signs Of A Bad Brake Booster Check Valve & Replacement Cost

There are many kinds of power brake boosters available today, but the vacuum brake booster is the most commonly used to give the driver an extra boost to the braking system when pressing the brake pedal. It’s designed to ensure a steady flow of hydraulic brake fluid to the brake master cylinder while increasing brake pressure and making it easier for you to put heavy vehicles to a halt. But, in order for this to work smoothly, the brake booster is dependent on the brake booster check valve.

These types of check valves rarely get inspected during routine maintenance or brake services. So unfortunately you won’t notice something is wrong until the check valve starts to malfunction

In this article, we will explore the signs of a bad or failing brake booster check valve, talk about its function, the replacement cost, and how you can test if the check valve is OK or not.

Let’s get started.

Signs & Symptoms Of A Bad or Failing Brake Booster Check Valve

These types of check valves rarely get inspected during routine maintenance or brake services. So unfortunately you won’t notice something is wrong until the check valve starts to malfunction

But if you’re experiencing one or more of these symptoms below, chances are you’re dealing with a bad brake booster check valve. Let’s take a closer look.

1. Increased Brake Pedal Effort

A properly functioning vacuum brake booster check valve ensures that applying pressure to the brake pedal is easy and smooth. However, when the valve breaks or cracks and can no longer remain sealed, it will likely create a vacuum leak. 

As the reduced vacuum in the booster means less boosting power, the operation of the brakes becomes much more difficult, requiring you to exert more force on the brake pedal to engage the vehicle’s brakes. Keep in mind that any inconsistency or changes in how your brake pedal feels should be seen as a warning sign. 

However, a faulty brake booster check valve should not be seen as the only culprit for a stiff brake pedal. A seized caliper, a bad brake booster, a cracked vacuum hose, or sludge in the brake lines are a few other typical problems that can cause the same symptom.

2. Spongy Feeling in the Brake Pedal

If the booster check valve is blocked, it won’t allow air to be sucked in from the vacuum brake booster. And if it breaks, air that the valve is supposed to keep out may find its way into the brake booster and end up in the master cylinder. It means that air bubbles can form in the brake lines and interfere with the smooth operation of the brake system.

Unlike brake fluid, air can be compressed. So next time you press the brake pedal, the air compresses instead of transmitting the force to the brakes immediately. This causes a spongy feeling in the brake pedal. And sometimes, the brake pedal may even sink to the floor.

As with a hard or stiff brake pedal, there are a number of reasons that could cause your brakes to feel spongy. Air in the brake lines is the most common reason, but this means you could also be dealing with leaking brake lines, low fluid levels, a defective master cylinder, or other problems.

If you want to learn more about it you can find a list here made by 

3. Check Engine Light

As mentioned, the brake booster check valve maintains necessary vacuum conditions by routing vacuum pressure from the engine. However, when the check valve develops a leak, it disrupts the measured airflow within the system, affecting the Mass Air Flow (MAF) sensor’s readings.

This disruption in airflow can lead to the engine running lean, meaning it receives more air relative to fuel than the ideal stoichiometric ratio. The vehicle’s Engine Control Unit (ECU) detects this imbalance and triggers the Check Engine Light to alert the driver of a potential problem.

Using a code scanner, you may identify Diagnostic Trouble Codes (DTCs) related to air-fuel ratios, confirming the issue is associated with the brake booster check valve. However, if the Check Engine Light does not coincide with braking trouble, it may indicate an unrelated issue with the engine.

Read more: Check Engine Light Turned off by Itself

4. Engine Performance Issues

So now we know that a faulty check valve can cause unregulated airflow in the induction system, disrupting the proper air-fuel mixture and causing the engine to run lean. As a consequence of this, the vehicle’s engine performance can be significantly affected and you may notice a drop in engine RPM and, in severe cases, even experience engine stall-outs.

It’s important to note that while a broken check valve can indeed be the root cause, there are other factors, such as a leaking brake booster diaphragm, that can lead to similar symptoms. In other cases, it could be non-brake-related problems.

This complexity underscores the importance of seeking a professional diagnosis to accurately pinpoint the source of the problem. If you observe any of these signs in your vehicle, it’s crucial to take action promptly. 

What are Brake Boosters?

A brake booster, also known as ‘power brake booster’, ‘brake servo’, or ‘vacuum booster’ is a dome-shaped device typically mounted towards the rear engine compartment wall. It helps to boost the power of the braking system and therefore reduces the force required to apply the brakes, making it easier for the driver to stop the vehicle. 

It consists of a chamber that is divided in half by a diaphragm and connected to a vacuum source, usually the intake manifold or a vacuum pump. The brake pedal is connected to one side of the booster, while the master cylinder is mounted on the other side

Prior to depressing the brake pedal, both chambers are provided with vacuum. However, when the pedal is pushed, the shaft moves forward, thereby opening the valve on the back of the chamber. Atmospheric pressure enters one half of the chamber, while the other half remains under vacuum. This pressure difference causes the shaft to move even further forward, ultimately pressing on the master cylinder pushrod.

Upon releasing the pedal, a spring prompts the shaft to return to its initial position, simultaneously returning the valves to their starting points. Consequently, vacuum pressure returns to normal on both sides of the diaphragm.

What Does a Brake Booster Check Valve Do?

The brake booster check valve is responsible to regulate and maintain the vacuum in the brake booster. Thanks to its one-way design it effectively expels trapped air as it also prevents any external air from entering the vacuum brake booster, even when the engine is off or if there is a leak in the vacuum hose.

This is a valuable safety feature that ensures you have power brakes and can safely pull over, even if the engine stalls. Together with the brake booster, these components create the vacuum-assisted brake system.

Here are the main functions of the booster check valve:

  1. It maintains vacuum in the booster
  2. Keeps air out of the master cylinder and brake lines
  3. It releases pressure buildup

Where Is The Brake Booster Check Valve Located?

Brake booster check in-line with vacuum hose

With most modern vehicles, the brake booster check valve is typically located on the brake booster. It’s a small, cylindrical component usually made of rubber or plastic. If you don’t find the check valve on the brake booster, it is likely installed in line with the vacuum hose.

As we already mentioned, the brake booster itself is a dome-shaped component positioned towards the rear engine compartment wall. While its appearance and exact location may vary depending on the make and model of your vehicle, it is typically found on the driver’s side, in line with the brake pedal.

You can easily find it by tracing the vacuum hose that connects to the intake manifold and leads to the engine and to the vacuum booster.

How Do You Test a Brake Booster Check Valve?

Since the check valve should maintain vacuum even when the engine is off, you can easily test the brake booster check valve by listening for a whooshing sound as you remove it from the brake booster.

With vacuum in the booster, you can follow the steps below:

  1. Park your car on level ground to ensure safety during the test.
  2. Open the car hood to access the engine compartment.
  3. Locate the brake booster, which is usually situated on the driver’s side of the vehicle near the firewall and in line with the brake pedal.
  4. Disconnect the check valve and hose from the brake booster.
  5. Listen for a whooshing sound after disconnecting the check valve and hose. If you hear the sound, it indicates that the check valve is functioning correctly, and the vacuum is being held.
  6. If you don’t hear any sound when these parts are removed, it means the check valve isn’t holding vacuum and needs to be replaced.

Note: If the check valve is located within the vacuum hose and cannot be serviced separately, you may have to replace the entire vacuum hose assembly along with the check valve. Be sure to check your vehicle’s service manual for the appropriate procedures.

Here’s how you replace the check valve:

  1. Before starting the replacement, ensure you have a new brake booster check valve that matches your vehicle’s make and model.
  2. Remove the gear-type clamp securing the vacuum hose to the check valve. 
  3. Loosen the screw head in a counterclockwise motion or squeeze the tabs together on a spring-type clamp to compress it and release the hose.
  4. Carefully remove the vacuum brake booster hose by twisting and pulling it. The twisting motion helps break the seal and makes it easier to detach the hose.
  5. Take out the old brake booster check valve from its position. If it’s stuck, you can apply some penetrating oil between the valve and the rubber grommet to ease its removal. Use pliers if necessary to grip the valve better and then twist and pull it out.
  6. Ensure the rubber grommet stays in place during the process; if it comes out, reinstall it on the brake booster.
  7. Install the new brake booster check valve into the rubber grommet securely. You can use penetrating oil to assist with this step if needed.
  8. Reconnect the vacuum hose by pushing it onto the barbed end of the new check valve.
  9. Reinstall the hose clamp to secure the connection. Make sure not to overtighten it.
  10. Test the vehicle in a safe location by driving it and trying out the brakes to see if they feel normal.

If there are any further issues, it’s recommended to have a professional mechanic inspect the braking system.

How Much Does It Cost To Replace A Brake Booster Check Valve?

When replacing a brake booster check valve, you can expect to spend $100 to $150 depending on the make, model, and where you choose to have the work done. However, it’s a DIY-friendly task which means you can come down to around $25 to €55 if you can perform the job yourself. 

But as a course of action, we do recommend seeking the expertise of a professional. If the check valve has been faulty for a while and affected other parts of the brake system, you may need additional fixes, such as bleeding the brakes. Unfortunately, this is something that may be necessary. Thus, the cost may increase.

When choosing a mechanic, make sure that they:

  • Are ASE-certified
  • Use high-quality parts
  • Offer service warranty


How long does the brake booster check valve last?

A brake booster check valve is designed to last for a long time and should ideally last as long as the car – if there are no unexpected issues. However, like any mechanical part, it can eventually wear out or fail over time due to various factors such as normal wear and tear, exposure to extreme conditions, or manufacturing defects.

Which direction does a brake booster check valve go?

Brake booster check valves are designed to allow the flow of vacuum only in one direction, specifically from the source to the servo device. These valves effectively block the reverse movement of vacuum from the power booster back to the source, ensuring efficient and controlled vacuum distribution in the system.

Why is my brake pedal hard after replacing a brake booster check valve?

If you’ve recently replaced the brake booster check valve and are still experiencing a hard brake pedal, it’s possible that the brake booster itself is defective. A malfunctioning brake booster can lead to similar attributes associated with a bad check valve, such as trouble braking or engine stalling.

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

Your brake pedal feeling “harder” than normal is one of the most common signs your brake booster has a vacuum leak. Sometimes, if there is a leak, you can hear a hissing sound from the brake booster. Other times, the check engine light may come on and you might experience engine performance issues.

Why is my brake booster check valve not releasing pressure?

If your brake booster check valve is not releasing pressure, the valve could be clogged, stuck, or mounted incorrectly. Remove the valve or vacuum hose and try sucking on one end. If you’re able to suck air, the end where you’re sucking from goes toward the engine. If the problem remains, you might have to replace it.

Is a brake booster check valve easy to replace?

Replacing a brake booster check valve is generally considered a relatively straightforward task. The exact ease of replacement can vary depending on the vehicle’s make and model, but in many cases, it’s as simple as twisting and pulling it out.


The brake booster check valve is a small but important part that’s necessary to work properly for smooth braking operation. Most people overlook this device when problems start to occur as many of the symptoms can be the same or associated with many other parts of the braking system. Fortunately, the check valve is relatively easy and inexpensive to replace and a professional mechanic should be able to make sure whether it’s bad or not.

That’s all for this article. If this guide helped you in any way, kindly share it with others. Thanks for reading!

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Rickard Cefalk

Rickard is the owner of and a dedicated and avid do-it-yourselfer who has always enjoyed working on his own vehicles since childhood. He now devotes his time to sharing his expert knowledge of car maintenance and other car-related information through his website.

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