Brake Booster Troubleshooting (Diagnose and Fix)

brake booster troubleshooting

The brake booster is an essential component of your vehicle’s braking system. It uses vacuum technology to assist in applying pressure to the brakes, making it easier to stop the car with minimal force on the pedal. However, like any technology, brake boosters can fail over time.

It’s crucial to be aware of the signs of a failing or faulty brake booster and take the necessary steps to diagnose and rectify the problem.

In this article, we will discuss the symptoms of brake booster failure, diagnostic tests you can perform at home, and how to fix common brake booster problems.

Symptoms of Brake Booster Failure

A failing or faulty brake booster can exhibit several warning signs. By recognizing these symptoms, you can identify the problem early and prevent further damage to your vehicle’s braking system.

Here are the most common symptoms of brake booster failure:

1. Hard Brake Pedal

A properly functioning brake booster should make the brake pedal feel easier to press down. When the booster starts to fail, you may notice that the pedal becomes harder to push down.

This increased resistance indicates a potential problem with the brake booster.

2. Extended Stopping Distance

A failing brake booster can compromise the power of your braking system, resulting in increased stopping distances.

If you find that your vehicle takes longer to slow down and stop, it could be a sign of a faulty brake booster.

3. Engine Stalls While Braking

When the seals inside the brake booster fail, it can cause the system to pull excess vacuum from the engine. This can lead to engine stalling as you depress the brake pedal.

Additionally, excessive vacuum pressure can cause brake fluid to enter the booster and damage the seals in the master cylinder.

If you experience any of these symptoms, it is crucial to address the issue promptly to ensure your safety on the road.

Diagnostic Tests for Brake Booster Problems

Performing diagnostic tests can help you identify the specific issue with your brake booster. Here are some simple tests you can conduct at home:

1. Basic Operational Test

Turn off the engine and pump the brake pedal 4-5 times with medium pressure. The brake pedal should stiffen noticeably after 2 pumps and become hard to press down after 4 or 5 pumps.

If the pedal becomes stiff immediately or after only 1 pump, there may be a vacuum leak or low engine vacuum affecting the brake booster’s functionality.

Inspect the vacuum supply hose for any kinks, cracks, or damage. If there are no visible issues, proceed to the next test.

2. Hard Brake Pedal Test

Turn off the ignition and pump the brakes 4-5 times until the pedal stiffens up. With light pressure, push down on the pedal and start the car. If the brake pedal gives slightly under your foot and stiffens up again, the brake booster is functioning correctly.

However, if the pedal stays stiff and does not drop or give under your foot, it may indicate a failing brake booster.

To determine if the problem lies in the power steering system, consult a mechanic for proper diagnosis and repairs.

3. Vacuum Supply Test

Turn off the ignition and pump the brake pedal 4-5 times to deplete the booster reserve. Connect a vacuum gauge to the vacuum supply hose and start the engine. Monitor the vacuum gauge while the car idles for a few minutes. A normal reading should be between 15” and 20” Hg (50 and 70 kpa) at idle.

If the reading is 16 or lower, inspect the vacuum hose for any kinks, clogs, or damage. If the hose appears fine, there may be mechanical issues such as leaky valves, worn rings, an intake manifold vacuum leak, or improper cam timing. Consult a mechanic for further evaluation.

4. Inlet Check Valve Test

Turn off the ignition and pump the brake pedal to deplete the booster reserve. Disconnect the vacuum supply hose from the booster. If the check valve is functioning correctly, you should hear a “whoosh” sound when disconnecting the hose.

Alternatively, you can blow into the vacuum supply hose and check if air passes through the valve into the booster. If there is no sound or air passing through, the check valve may need to be replaced.

Read also >> Brake Controller Troubleshooting (Here Is What To Do)

Read also >> Secondary Collision Brake System Malfunction (How To Fix)

How to Fix Brake Booster Problems

If your diagnostic tests confirm that your brake booster is faulty, it is essential to address the issue promptly to ensure your safety on the road.

Fixing a brake booster generally involves replacing the entire unit. However, the exact procedure may vary depending on the design of the booster.

If the booster is accessible with common hand tools, you may be able to replace it yourself. However, some boosters have a crimped design, requiring special tools and equipment for replacement. If you are unsure or lack experience, it is recommended to have a qualified mechanic handle the replacement.

The cost of brake booster replacement can vary depending on the make and model of your vehicle and the specific parts that need to be fixed or replaced.

On average, brake booster replacement costs between $325 and $1,250, including labor.


The brake booster plays a crucial role in your vehicle’s braking system. Recognizing the symptoms of brake booster failure and performing diagnostic tests can help you identify and address issues early.

If your brake booster is faulty, it is important to have it replaced promptly to ensure your safety on the road.

Consult a qualified mechanic for proper diagnosis and repairs. By maintaining a properly functioning brake booster, you can enjoy optimal braking performance and peace of mind while driving.

Steve P.

Steve is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Riviera. Steve is based in Boise, Idaho.

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