Faulty Brake Booster Symptoms

Brake Booster Symptoms

If you've ever experienced issues with your car's braking system, you know how scary and dangerous it can be, which is why you need to understand when it has gone bad so that you can fix it.

A critical component of the braking system is the brake booster (also known as the brake proportioning valve), which helps to distribute the hydraulic pressure to each brake evenly.

When the brake booster isn't functioning correctly, you may experience symptoms like uneven braking, brake lock-up, or a soft brake pedal.

In this post, we'll go over the most common faulty brake Booster symptoms, what can cause it to malfunction, how to diagnose the issue, and options for repairing or replacing it.

Faulty Brake Booster Symptoms

If you've noticed that your car's brakes are acting a little wonky lately, it could be due to a problem with the brake vacuum. According to yourmechanic.com, the Brake Booster ensures the hydraulic pressure from the brake system flows evenly to each wheel.

You'll notice some telltale, alarming, and potentially dangerous symptoms when it's not working correctly.

Below outlined are the faulty brake booster symptoms.

1. Engine Stalls When Applying Brakes

One common symptom of a faulty brake booster is an engine that stalls when you apply the brakes.

This problem can occur when the brake booster malfunctions and causes the brakes to lock up, leading to the engine stalling.

It is a serious problem that requires immediate attention as it could cause a severe driving accident.

2. Longer Stopping Distance

Another symptom of a faulty brake booster is a longer stopping distance than you are used to.

If your brakes are not functioning as effectively as before or if it's taking longer to come to a complete stop, it could indicate that the brake booster is not distributing pressure evenly.

This issue can be hazardous in emergencies when you must stop quickly.

3. Hard Brake Pedal

A hard brake pedal is another symptom of a faulty brake booster. The brake pedal will feel stiff and requires more pressure than usual to stop the car.

A malfunctioning brake booster can cause insufficient force to reach the brakes, making it harder to stop the vehicle.

4. Raised Brake Pedal

A bad brake booster can be detected when a brake pedal is higher than usual. While this may go unnoticed by many drivers, those who pay close attention to the feel of their vehicle while driving may notice that the brake pedal is stiffer than usual when pressed.

5. Warning Lights

When brake boosters get faulty, they can trigger warning lights on your dashboard.

These lights come on when specific sensors in your braking system detect that something is wrong. If you see the brake warning light come on, it's a sign that something is wrong with your brakes.

Low fluid levels, a bad master cylinder, and other issues can all cause these warning lights to turn on.

6. Fluid Leaks

A fluid leak in the braking system is also another indicator of a bad brake booster, particularly when the leak is around the brake pedal.

Hydro-boost brake boosters use power steering fluid; when they develop a leak, some fluid that makes them function effectively can be lost.

7. Hissing Sound

If you hear a whizzing sound coming from under the dashboard or near the brake pedal when you push the brake pedal down, it could signify that the brake booster is bad.

This noise occurs when the vacuum in the brake booster starts to escape. If the hissing sound comes from your engine bay or brake pedal areas, it's likely a symptom of a bad brake booster.

Causes of Brake Booster Symptoms

Several things can cause a brake Booster to fail and lead to brake problems. Below are common causes of brake Booster symptoms:

1. Owner Neglect

Many people need to realize that paying attention to regular maintenance on their brakes can reduce the buildup of contaminants in the brake system.

Over time, these contaminants can damage the brake Booster and cause brake problems. This is why checking your brakes regularly and replacing the brake fluid as needed is essential.

2. Leaking Hydraulic Fluid

A leak in the brake system, such as from a damaged brake line or a failed brake caliper, can cause a loss of hydraulic pressure.

When this happens, the brake Booster may not distribute pressure evenly to each wheel, leading to brake problems. It's essential to have any brake leaks addressed promptly to avoid damage to the brake Booster.

3. Damaged Rotor Disks

If the brake rotors are damaged or warped, it can cause issues with the brake Booster. The brake rotors are an essential component in the braking system and are responsible for slowing down and stopping the car.

If they're damaged, it can cause the brake pads to wear unevenly, leading to problems with the brake Booster.

4. Overheating Brake Pads

Overheating brake pads can be another problem that leads to a faulty brake Booster. This can happen when the brakes are used excessively, such as driving down a long hill or towing a heavy load.

When the brake pads overheat, they can damage the brake Booster and other components in the braking system.

5. Overloading Your Automobile

Overloading your car with too much weight can strain the braking system, including the brake Booster.

When the brakes are under more pressure than they can handle, it can cause damage to the brake Booster and other components in the braking system.

6. Driving Through Mud or Water

When you go through mud or water, it can cause damage to the braking system, including the brake Booster.

Mud and water can get into the brake components and cause them to wear out or fail over time.

7. Loss of Hydraulic Brake Fluid Pressure

If the hydraulic brake fluid pressure is lost, the brake Booster can malfunction and cause brake problems.

This issue can happen if there's a leak in the brake system or the brake fluid is low. It's vital to check the brake fluid level regularly and have any leaks repaired promptly.

Diagnosing a Faulty Brake Booster

To diagnose a faulty brake booster, follow the steps highlighted below:

Step 1: 

Sit in the driver's seat and start the engine, setting the transmission to park (if it's an automatic) or neutral (if it's manual). Ensure the emergency brakes are engaged, and let the engine idle for a couple of minutes before shutting it off.

Step 2:

Pump the brake pedal at normal foot pressure four times and hold your foot down on the pedal slightly.

Step 3: 

Start the engine. As the engine starts, you should feel the brake pedal move downward slightly, about an inch or less.

If you don't feel any movement, this could indicate that there isn't enough vacuum in the brake booster. You can do engine vacuum and brake booster tests to locate the fault.

After this, while the engine is still idling, remove your foot from the brake pedal and turn off the engine.

Now, depress the brake pedal using normal foot pressure four times. If you notice the pedal rising after the second or third time you depress it, the booster is more likely holding a vacuum.

However, if you don't feel the pedal rising, this could indicate a vacuum leak affecting booster performance.

To locate the problematic area, you'll need to test the engine vacuum and brake booster performance using a vacuum gauge and a handheld vacuum pump, as described in the following sections.

Step 4: 

Next, start the engine and let it idle.

Then, push down on the brake pedal and turn off the engine, but keep the pedal depressed for about 30 seconds after shutting off the engine.

If the pedal doesn't hold its position, this could indicate a leak in the brake booster, valve, vacuum hose, or intake manifold. You should check the vacuum hose, booster check valve, engine vacuum, and brake booster.

If you feel the brake pedal is too hard while driving and the vacuum hose and check valve seem to work fine, you may need to replace the brake booster.

Brake Booster Replacement Cost

If you're experiencing issues with your brake Booster and need to replace it, you might wonder how much it will cost. According to the experts at Repair Smith, the cost of a brake Booster replacement can vary depending on several factors.

On average, you can expect a brake booster replacement to fall anywhere between $325 to $1,250. This cost includes parts and labor, which can vary significantly depending on the make and model of your vehicle and the mechanic's labor rates.

In terms of labor costs, you can expect to pay anywhere from $100 to $200 for the brake Booster replacement.

The parts can range from $100 to $900 or more, depending on the specific components needed for your vehicle.

It's important to remember that your vehicle's make and model will largely determine the cost of a brake Booster replacement. If you drive a luxury car, the cost of the replacement parts will likely be much higher than for a standard vehicle.

Additionally, the labor rates can vary depending on the mechanic and their level of expertise.

In any case, getting a few quotes from different mechanics is always a good idea to ensure you're getting a fair price. Choosing a reputable mechanic with experience working on your vehicle make and model is also essential to ensure the proper replacement and safety.


A faulty brake booster can cause serious safety issues while driving, so it's crucial to address any brake booster symptoms immediately.

While the cost of a brake booster replacement can vary depending on various factors, it's critical to prioritize safety over cost and resolve the issue with a trusted mechanic as soon as possible.

Whether you're experiencing engine stalls, longer stopping distances, or a hard brake pedal, it's essential to diagnose the root cause of the issue and get it addressed before it causes any further damage or safety concerns.