If you notice a decrease in brake pressure on your vehicle, it could be a number of issues, but the common culprit is the brake booster. The brake booster is a canister with dual chambers and a rod running through it. When you press the brake, the brake booster vacuum system sends air into one chamber, and the other chamber holds the vacuum. Here are some tips to test for a faulty brake booster.

Test the Booster Resistance

Park the vehicle on a flat surface. Shut off the engine, and press the brake five or six times applying normal pressure to release air from the chambers.

Turn on the engine, and let the engine idle for about two minutes. Press the brake, keep it down, turn the engine off, and pay attention to resistance.

If the booster is working properly, the pedal will drop all the way to the floor, and resistance should decrease. If you don't feel anything, the booster is faulty.

Check the Vacuum Hose

Start the engine, and let it get to moderate speed. Shut the engine off, and release your foot from the gas. After a minute and a half, press the brake.

If the hose is faulty, the pedal will push back against your foot, or you may hear a whining sound. This means the vacuum hose has a hole the air passes through.

If the vacuum hose looks intact, test for leaks with a pair of pliers. Open the hood, start the engine, and place a pair of pliers between the engine and the booster.

Gradually pull the check valve (the rubber diaphragm that rest between the engine and the brake) from the booster, taking care not to loose the rubber grommet. Place one finger over the check valve. Remove the pliers, and listen for hissing sounds, which indicate a leak.

Test the Check Valve

If you didn't detect a leak on the vacuum hose, test the check valve. Set the valve back in place, shut the engine off, and remove the valve again. You should hear a woosh sound when you remove the valve to indicate the brake booster is able to hold a vacuum.

If you don't hear a noise, or you hear a little noise, test the suction of the valve. Blow air through one end of the valve. Air passing through both sides means the valve is good, and the brake booster needs replacing.

It is important that the brake system works properly to ensure driving safety. If you suspect a faulty brake booster, but you don't trust your skills to replace it take the vehicle to an auto service such as Budget Automotive Center.