Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Power Brake Booster
The brake servo serves to amplify braking force and, simply put, comprises two chambers - one front and one rear. There are two main types of brake servos - passive and active. The brake servo is mounted on the cowl panel in the engine compartment.
There are four versions of brake servo that are tied to the type and equipment of the vehicle.
| Vehicle equipped with brake servo of type: | Vehicle equipped with/without adaptive cruise control function | |||
| Adaptive cruise control (ACC) and without brake vacuum pump | Adaptive cruise control (ACC) and with brake vacuum pump | Without adaptive cruise control (ACC) and without brake vacuum pump | Without adaptive cruise control (ACC) and with brake vacuum pump | |
| Active brake servo with vacuum pressure sensor | X | |||
| Active brake servo without vacuum pressure sensor | X | |||
| Passive brake servo with vacuum pressure sensor | X | |||
| Passive brake servo without vacuum pressure sensor | X | |||
Passive brake servo
The passive brake servo amplifies the driver's braking force by allowing atmospheric pressure into the rear chamber while the front chamber maintains a vacuum pressure. This creates an amplification factor.
The passive brake servo can be equipped with a vacuum pressure sensor if the vehicle does not have a brake vacuum pump.
Passive brake servo without vacuum pressure sensor
The passive brake servo consists of:
- vacuum cylinder
Passive brake servo with vacuum pressure sensor
The brake servo consists of:
- vacuum cylinder
- vacuum pressure sensor
Active brake servo
The active brake servo has the qualities of the passive brake servo, but can also be activated by the brake control module (BCM) regardless of whether the driver is braking. An active brake servo is equipped with a pressure valve and a pedal pressure sensor. In order to create brake pressure without the driver depressing the brake pedal, the brake control module (BCM) activates the pressure valve, which allows atmospheric pressure into the rear chamber. The brake control module (BCM) uses information from the pedal pressure sensor to be able to detect whether the driver is braking when the active brake servo is operating.
The active brake servo is also equipped with a pedal position sensor.
The active brake servo can be equipped with a vacuum pressure sensor if the vehicle does not have a brake vacuum pump.
Active brake servo without vacuum pressure sensor
The brake servo consists of:
- vacuum cylinder
- connector for pedal pressure sensor and pressure valve
- pedal position sensor
Active brake servo with vacuum pressure sensor
The brake servo consists of:
- vacuum cylinder
- connector for pedal pressure sensor and pressure valve
- pedal position sensor
- vacuum pressure sensor
NO RELATED
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
Affiliate disclosure: We may earn a commission at no extra cost to you.
When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.