The brake booster is a crucial helper in your car’s braking system. It sits between your brake pedal and the main part that sends fluid to your brakes (master cylinder). When you push the brake pedal, the booster multiplies that force, making it much easier for you to apply the brakes with less effort.

There are three main types of brake boosters:

Vacuum Booster: The most common type, often found in gasoline cars. It uses engine vacuum to create power assist.
Hydro-Boost Booster: Frequently seen in diesel vehicles, this type uses your car’s power steering system to provide the boost.
Electrohydraulic Booster: Most commonly found in hybrid cars, this type uses an electric pump to create hydraulic pressure for boosting.

Simple Signs of a Bad or Failing Brake Booster

A faulty brake booster can cause various problems, making your brakes feel “off.” Here are the common signs, grouped by the type of booster:

Problems Common to ALL Brake Booster Types:

Hard Brake Pedal: This is a key sign. If your brake pedal feels unusually stiff and hard to push down, it means the booster isn’t helping you enough.
Longer Stopping Distance: Because you’re not getting the full braking power, it will take your car longer to come to a complete stop, which is dangerous.

Problems Specific to a Vacuum Booster:

“Check Engine Light” On and Engine Acts Up: A leak in a vacuum booster can steal “vacuum” from your engine, which can turn on the check engine light. Your engine might also run roughly, and it could even stall, especially when you apply the brakes.
Hissing Noise: You might hear a distinct hissing sound, particularly when you press the brake pedal, indicating a vacuum leak in the booster.

Problems Specific to a Hydro-Boost Booster:

Fluid Leaks (Power Steering Fluid): Since hydro-boost systems use power steering fluid, a faulty booster can cause power steering fluid to leak. If the leak is bad enough, you might also notice that steering becomes harder, especially at low speeds.
“Grabby” Brakes: An internal problem with the hydro-boost unit can make your car feel like it’s jerking or grabbing unevenly when you brake.

Problems Specific to an Electrohydraulic Booster:

ABS or Traction Control Lights On: A computer monitors this type of system. If there’s a problem with the electrohydraulic booster, it can cause the ABS warning light or traction control light to illuminate on your dashboard.
Fluid Leaks (Brake Fluid): A faulty electrohydraulic booster can cause brake fluid leaks.
“Grabby” Brakes: Similar to hydro-boost, an internal issue in an electrohydraulic booster can cause the brakes to feel grabby or jerky.

How to Fix a Failing Brake Booster

If you’re having any kind of braking problems, it’s not safe to drive your car. Have it towed to a mechanic who can properly diagnose and fix the issue.

Diagnosing problems with vacuum or hydro-boost systems is often straightforward. A mechanic might simply need to feel the brake pedal with the engine running to tell if the booster is at fault. They’ll then perform specific tests: for vacuum systems, they might test for vacuum pressure; for hydraulic systems, they’ll measure the hydraulic pressure going into the booster.

If the brake booster is faulty, it will need to be replaced. This involves disconnecting it from the master cylinder, removing any vacuum or hydraulic lines, and then taking out the booster itself before installing a new one.

This is a job best left to your mechanic, especially for the more complex electrohydraulic units. After replacement, both hydro-boost and electrohydraulic systems will need to have air “bled” out of them, and all four wheels’ brakes will need to be bled as well to ensure proper operation.