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ABS - prevents the wheels from locking up during
braking, maintaining steerability and directional
control during deceleration
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ASR, EBR and ESP Functions
ASR (braking moment) - prevents drive wheel from spinning while driving.
EBR - reduces brake slip at the drive wheels during deceleration to ensure
ESP - prevents the vehicle from breaking away when oversteering or
The major difference between any of these modes and the normal braking or ABS mode is the fact that the
driver has not operated the brake pedal, the ESP control module (N47/5) has initiated the pressure request.
EBR is actually a function of E-Gas. (It is mentioned here as a review of the system function even though
A7/3 is not hydraulically involved.) When engine braking causes the rear wheels to reduce speed quicker then
the front wheels (causing the rear of the vehicle to slide), the throttle is opened slightly to reduce the engine
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During continuous brake applications, the brake
fluid in the calipers may heat up and expand.
(Front wheels only.) As the volume of the brake
fluid at the wheel side of the media separators (7
& 8) are locked in by the separation valves, it is
not possible for any volume compensation to
take place in the direction of the reservoir during
brake application. If the media separator is now
in the basic position of the specified pressure,
the pressure must be dissipated differently in
order to set the specified pressure.
Temperature compensation is achieved by
pulsed opening of the separation valves at the
Note: The driver may notice the brake pedal
pulsating during this operation.
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SBC is functional as soon as it is “wakened” by:
• opening a door (from N10/8)
• operating the central locking system (from N10/8
• depressing the brake pedal
• turning the key to position 1
• releasing the parking brake
The wake up signal comes from the left front SAM
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Predrive Check (PDC)
SBC may perform a PDC after waking, the following are checked:
• reservoir pressure (and corrected if necessary)
• pressure sensors (~ 60 bar of pressure applied to each wheel)
• control valves
• leak tests
• operational checks
The PDC is cancelled if the driver operates the accelerator.
Self-test of the separation and balance valves are constantly
conducted during driving. (About every 16 brake applications.)