Bad Brake Booster Check Valve Symptoms to Be Aware of

Nobody on earth likes car malfunctions, but a brake problem is a different thing altogether. Brake issues can be extremely dangerous, especially if it fails in a critical situation. This can endanger the life of the driver, passengers, and other road users.

This article will discuss bad brake booster check valve symptoms, causes, meaning, and how to test it. We’ll also explain what happens when a brake booster check valve goes bad. So grab a seat and a cup of coffee while we explore everything you need to know about brake booster check valves.

brake booster check valve cost

What is a brake booster check valve?

A brake booster check valve is a valve that prevents air from getting into the brake system when you release the braking pedal. This component sucks out air from the brake booster barring additional air from getting into the booster, allowing the brake booster to augment the force from the braking pedal.

The check valve prevents air bubbles from building up in the brake lines, which can greatly affect the overall brake performance. The check valve connects the brake booster to a vacuum port, making it a safety solution that enables the brake to work even when the car is not running.

What does the brake booster check valve do?

The brake booster valve connects the brake booster to a vacuum hose from the inlet manifold. When you depress the braking pedal, the brake booster check valve sucks air from the inlet manifold, forming a vacuum.

The vacuum pushes the diaphragm, which forces the hydraulic in the brake master to travel to the wheels, increasing the braking power. As explained above, it is a one-way valve. This means it sucks the air out of the brake booster while preventing air from getting into the system. This helps to maintain the vacuum in the system.

Bad brake booster check valve symptoms

Mechanics and DIYers do not inspect the check valve during routine maintenance, but it can show signs when it begins to wear out or has failed. So, what are the symptoms of a faulty brake booster check valve you should watch out for?

The common signs of a bad brake booster check valve are a spongy brake pedal, the need to pump the braking pedal several times before braking, and a sinking brake pedal. The best solution is to replace the check valve because repairing it is a game of chance.

These are common warning signs that need an experienced service technician to diagnose and fix. However, these signs can also emit from other faulty brake components.

Spongy brake pedals

If the brake booster check valve problem stays longer, it will allow air bubbles to travel down to the brake lines and eventually to the wheels. In this case, the check valve that is supposed to remove air from the system and prevent air from entering now allows air to enter the brake master and travel down to the brakes.

Once this happens, the pressure in the brake lines will be reduced, and the brakes will be applied softly. For this reason, the braking pedal will feel spongy when driving, but the braking distance will increase.

At this point, you need to go for a brake inspection. Since brakes are hydraulically controlled, a failed check valve will trap any air that enters the brake lines. The only solution to remove the trapped air is bleeding the brake system. 

Longer stopping distance

If the check valve fails, air will get into the system, and there will be no vacuum to brake effectively. This will drastically reduce the force from the braking pedal when you step on it. You’ll exert more force on the pedal to slow or stop the car. This means there will be a longer stopping distance. And, of course, this will increase the risk of collisions.

Brakes stop working

In a worst-case scenario, the brakes will fail completely. I hope you won’t get to this point. But if you find yourself in this situation, find a way and stop the car and call a tow van to tow your vehicle to your auto repair center and fix the brake.

In such a situation, the braking pedal will fall to the floor when you depress it. The risk of getting into a road accident is high. Depending on the leading cause, the solution could be replacing a brake booster check valve or other brake system components. Brake booster check valve problems are something you don’t want to ignore.

how to clean brake booster check valve

How do you test a brake booster check valve?

As reiterated above, the check valve in the brake booster is a safety feature that holds the vacuum inside the brake booster when the vehicle is off. Without this component, the brake will fail if the engine turns off on the road. With a functioning check valve, there will be enough vacuum to hold the brakes even when the car is off.

With this explanation, you should know how to test a brake booster check valve. The simplified way to know if you have a bad check valve on the brake booster is to turn off the engine and disconnect the hose. If the check valve makes a whooshing sound when you disconnect it, it is working properly. But the check valve is bad and needs replacement if you don’t hear any sound.

How to replace brake booster check valve

Replacing a bad brake booster check valve is the best fix, and the process is simple. Firstly, locate the check valve on the brake booster and disconnect it. Next, gently remove the retaining clips or nuts for easy disconnection.

Grab the new check valve and install it following the reverse process. Make sure you clamp the retainer properly. However, you need to inspect the system and fix any vacuum leaks. If not, air will still enter the system and cause vacuum loss.

Lastly, inspect the brake master cylinder and change it if necessary. This is intermediate to the advanced repair job. So, if you’re a beginner DIYer, have an experienced mechanic do the job.

How much does it cost to fix a bad brake booster check valve?

Factors like car make and model, taxes, location, and repair shops, affect the cost of fixing a brake booster check valve. However, the average cost of replacing a check valve is between $85 to $100. The brake booster check valve cost should be $40, while the labor cost should be around $45 to $60. This does not include shipping fees and taxes.


Does the brake booster need a check valve?

Yes, brake boosters need the check valve to offer optimum performance. Without the brake booster check valve, the brake will not work when the car is off. Again, without the check valve, air will enter the brake lines. When this happens, the brake system efficiency will be reduced.

Can a bad brake booster check valve cause a hissing noise?

It is possible. A hissing noise is a sign of a vacuum leak in various systems. If the hissing noise comes from the brake booster area, you could have a vacuum leak from the diaphragm, hose, or check valve.

How Long Does The Brake Booster Check Valve Last?

A check valve on the brake booster should last the lifespan of the vehicle. This component will hardly get any maintenance due to its location. The only time you have to touch this component is when it goes bad or when replacing the brake booster. However, this component can fail as it may not work for the lifespan of the vehicle.

Final Words

If you’re experiencing a bad brake booster, check valve symptoms, diagnose, and fix the leading cause. Ignoring this problem will increase the risk of road accidents.

We’ve explained how to replace a brake booster check valve, the common signs, and how to test it in simplified ways. You can follow the above guides to track the cause if you are familiar with the brake mechanism. However, a check valve is a safety feature. Have a service technician do a thorough inspection and proffer a solution if you’re a beginner DIYer.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

3 thoughts on “Bad Brake Booster Check Valve Symptoms to Be Aware of

  1. Hey Todd,

    I appreciate your time here. But trust me, this time, you are wrong.

    The check valve is designed to suck out air that is trapped in the brake booster without letting additional air enter the cylinder. This protects the brake lines from developing an air bubble, which can seriously impact braking performance.

  2. Bad advice on the purpose and function of the brake booster check valve. The vacuum booster operation has NOTHING to do with the physical brake lines or allowing air to enter the hydraulic system. Check your facts. This is VERY basic. If this is not understood then, advice should not be offered.

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