Symptoms of a Bad or Failing Vacuum Brake Booster Check Valve

Many vehicles employ a vacuum brake booster in order to provide additional power to the braking system. It's designed to provide consistent flow of hydraulic brake fluid to the brake master cylinder while increasing brake pressure and helping heavy vehicles stop more easily. This component is common on a variety of consumer cars, trucks and SUVs. From time to time, the vacuum brake booster is susceptible to damage or typical wear and tear. This includes the brake booster check valve.

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. This part connects the body of the brake booster to the vacuum hose and is a safety solution that still allows the brakes to work – even if the engine is shut off.

Typically the vacuum brake booster check valve is not inspected during routine maintenance, but there are times when this part can show signs of wearing out or that the booster check valve has failed entirely. Here are a few of those warning signs so you can determine if a potential problem with your vacuum brake booster check valve exists. Remember, these are common warning signs that should be professionally diagnosed by a certified mechanic and properly repaired.

1. Brake pedal is difficult to engage

When the vacuum brake booster check valve is working correctly, applying pressure to the brake pedal is easy and very smooth. When the check valve is not working correctly, the operation of the brakes becomes much more difficult. Specifically, the pedal goes from smooth and soft to aggressive and very difficult to press down. This is due to the excess pressure inside the master cylinder, which the check valve is designed to regulate. The inconsistency of the brake pedal is a warning sign that a potential safety issue exists with the brakes and should immediately be inspected by a certified mechanic.

2. Brakes feel spongy

As the problem with the vacuum brake booster check valve increases, air bubbles will progressively move down the brake lines and to the brakes themselves. In this case, the air that is supposed to be removed by the check valve enters the master cylinder and then into the brake lines. This causes a reduction of pressure inside the brake lines and can cause the brakes to be applied softly. While driving it will feel as if the brake pedal is spongy, however, the brakes will also take longer to stop the vehicle.

This situation calls for an immediate inspection of the brake system. When air enters the brake lines, it typically becomes trapped due to the fact that brakes are hydraulically controlled. In order to remove the air from the brake lines, the brake system will have to be bled. As such, when you experience a problem like this in your vehicle, stop driving it as soon as possible and have the entire brake system professionally examined.

3. Brakes stop working

The worst-case scenario occurs when the vacuum brake booster check valve completely breaks and eventually leads to a brake system failure. Hopefully you never get to this point, but if you do, safely stop the car, have the vehicle towed back home and contact a mechanic who is certified with brake system inspections and replacement. Depending on what actually broke, the repairs can range from simple vacuum brake booster check valve replacement to complete brake system repair and replacement.

The vacuum brake booster check valve is important to your braking system, and acts as a safety feature. It's due to these facts that the problems and symptoms above should not be ignored or put aside for another day. Contact a certified ASE mechanic to inspect, properly diagnose, and make appropriate service adjustments to your brakes.


Next Step

Schedule Brake System Inspection

The most popular service booked by readers of this article is Brake System Inspection. Once the problem has been diagnosed, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. YourMechanic’s technicians bring the dealership to you by performing this job at your home or office 7-days a week between 7AM-9PM. We currently cover over 2,000 cities and have 100k+ 5-star reviews... LEARN MORE

SEE PRICING & SCHEDULING

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Recent Brake System Inspection reviews

Excellent Rating

(334)

Rating Summary
309
14
4
1
6
309
14
4
1
6

Jesse

17 years of experience
127 reviews
Jesse
17 years of experience
Jaguar S-Type V8-4.2L - Brake System Inspection - Palm Coast, Florida
Jesse showed up for the appointment timely and ready to work. He was polite and professional and competent. He took sufficient time to inspect the vehicle and explained in layman's terms any problems and whatever corrective work that might be required. I highly recommend Jesse and hope to have him service my vehicles again in the future if needed.
Ford Escape - Brake System Inspection - Daytona Beach, Florida
Jesse arrived on time after sending notice 15 mins prior. A true professional Jesse got right down to business. He started his inspection work right away and did a thorough professional job and determined the solution to his findings. I am very pleased. He is a true expert mechanic.

Johnny

34 years of experience
392 reviews
Johnny
34 years of experience
Toyota RAV4 L4-2.4L - Brake System Inspection - Sacramento, California
Johnny arrived early which was great, he performed the inspection in less than half an hour, and gave us a complete quote for all items needing attention, including the brakes as our main concern. Johnny is fast and efficient so I scheduled the work done by him.
Ford Escape - Brake System Inspection - Sacramento, California
The convenience is worth the cost. I was also tired of the dealership not really caring about my old car. Last couple of times I had to wait well over an hour to get my car after the dealership said "It's ready!". They also wouldn't fix the things I asked saying they didn't have time and I need to come back.

Luis

30 years of experience
119 reviews
Luis
30 years of experience
Honda Accord V6-3.0L - Brake System Inspection - Northbrook, Illinois
He's excellent. On Time, honest and all repairs done quickly and correctly. Book him if he's available!

Christopher

16 years of experience
246 reviews
Christopher
16 years of experience
Nissan Sentra L4-2.0L - Brake System Inspection - Charlotte, North Carolina
Very informative and made sure to clarify on what he spoke on so that I understood what was happening with my car

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

Related articles

How to Adjust a Parking Brake Shoe
Before you begin, it’s important to be familiar with your specific parking brake (https://www.yourmechanic.com/services/parking-brake-won-t-engage-inspection) system. While all systems accomplish the same...
How to Replace a Cruise Control Brake Release Switch
The cruise control is turned off by the brake release switch which fails either when the cruise control does not deactivate or does not set properly.
How to Replace a Power Brake Booster
Replacing a power brake booster can be challenging, as it requires several steps and the proper tools to do so.

Related questions

Changing the rims and tires. Will I also have to replace the brakes to match?
Changing to a higher aspect ratio tire, for example in your case moving from 205/50 R17 to 195/65 R15, will improve ride comfort due to the greater sidewall height. The brake rotor diameter, and the brake rotor part number, is...
Cause of steering wheel vibration at 40
If you are getting a braking vibration that seems to be present above 40 mph when braking is most likely the front rotors are slightly warped. As the warpage gets worse then the pulsation will be felt at even slower...
I had a new rear brake sensor installed. The braking lights still come on intermittently.
Check all of the sensors and switches on the brake system and make sure all of them are connected properly. Make sure that all of the connections are clean and have no bent or broken pins. The brake warning light...

How can we help?

Our service team is available 7 days a week, Monday - Friday from 6 AM to 5 PM PST, Saturday - Sunday 7 AM - 4 PM PST.

1 (855) 347-2779 · hi@yourmechanic.com