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Electric Brake Booster System Description
Overview
The electric brake booster is an electromechanical brake booster that replaces a typical vacuum brake booster. This system provides stable braking performance that does not depend on vacuum supply. The electric brake booster system consists of the following primary components:
For locations of each component on the vehicle, refer to Component Location Index, and for functions of the indicator, refer to How to Troubleshoot the Electric Brake Booster System. Construction
The electric brake booster consists of the servo component, the servo control component, and the master cylinder component. The servo component consists of the motor, the gear unit, and the boost body. The assisting force generated with the motor is transmitted to the boost body through the gear unit, and an assist is performed because the boost body moves the piston of the master cylinder through the reaction disc. The servo control component consists of the electric brake booster control unit, the motor angle sensor, and the brake pedal stroke sensor. The electric brake booster control unit is calculating the location of the boost body from the motor angle information measured by the motor angle sensor. The location of the plunger is measured based on the signal from the brake pedal stroke sensor. The master cylinder component is equivalent to a conventional vacuum brake booster brake system.  Servo Control Operations
When the driver presses down the brake pedal, the master cylinder piston is pushed by the driver's pedal force via the input rod, the plunger, and the reaction disc. The plunger moves at this time, but the boost body connected with the motor through the gear unit does not move because the motor is not active. As a result, there is a difference between the relative position of the plunger and the boost body. The control unit drives the motor to generate the required assisting force which is calculated based on the relative position of the plunger and the boost body. The assisting force created by the movement of the boost body is transmitted via the reaction disc to the master cylinder piston.  Fail-safe
During the fail-safe mode, the driver's brake pedal operating force is transmitted via the reaction disc to the master cylinder piston directly. The hydraulic pressure created by the brake pedal force activates the brake caliper. In the fail-safe mode, the electric brake booster requests the hydraulic boost failure compensation control to the VSA modulator-control unit.  Engine Starting Prohibition Condition
Vehicles equipped with the electric brake booster have starting restrictions.
The engine may only start under the following conditions:
For more information, refer to the Fuel and Emissions Construction and Function. System Wake-Up and Shutdown
The electric brake booster system is activated when the driver's door is opened while the vehicle is in the OFF (LOCK) mode or when the vehicle is turned to the ON mode. The system will shut down automatically 3 minutes after the driver's door was opened with the vehicle in OFF (LOCK) mode. Once the driver's door is opened and the system is activated, the system's activation time will not be extended because the door was opened again. Open the driver’s door
 Turn the vehicle to the ON mode after opening the driver’s door
 Open the driver’s door again after the system is activated by opening the door
 Open the driver’s door after turning the vehicle to the OFF mode from ON mode
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