BAS brake application, function

Instrument cluster A1

BAS
control unit N48

Voltage

ABS terminal 87

Diagnostic data link connector X11/4

Traction system control unit N47

(ABS/ETS/ASR/ESP)

Indicator lamp

BAS (A1e39), BAS/ETS (A1e49), BAS/ASR (A1e48),

BAS/ESP (A1e47) or

Multifunction display (A1p13)

Brake booster

A7/7/7

Diaphragm travel sensor A7/7b1

BAS release switch A7/7s1

BAS solenoid valve A7/7y1

Terminal 30

Terminal 31

Stop lamp switch S9/1

Left front rpm sensor L6/1

Right front rpm sensor L6/2

CAN

Data bus

The functions of the BAS brake booster (A7/7) are controlled using the components of the electric/electronic system.

In model 168, the voltage supply for the BAS control unit (N48) is via the fuse and relay box (F1). In models 129 and 140 via the base module (N16/1). In models 163, 170, 202, 208, 210, 215, 220 via the relay module (K40). In models 203 and 209 via the SAM control unit (N10/1).

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In all vehicles with engines 112, 113, 605, 606, 611, 612, 613 and ESP, the BAS control unit function is integrated in the ESP control unit (N47-5).

In models 163, 168, 203, 209, 215, 220 the BAS control unit function is integrated in the ESP control unit (N47-5).

The BAS control unit receives input signals from the following components:

 ME control unit (via CAN data line)

 Traction system control unit (via CAN data line)

 BAS diaphragm travel sensor

 BAS release switch

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In the BAS control unit, the input signals are converted into output signals for the following components:

 BAS solenoid valve

 BAS/ESP indicator lamp (via CAN data line)

On the basis of the input signals, the BAS (N48) or ESP (N47-5) control unit decides which of the 3 operating modes

 Normal mode

 BAS pressure increase

 BAS pressure reduction

is to be activated.

Normal operation

In this case, the brake application is not at the higher pedal speed (that requires activation of BAS). The solenoid valve in the BAS brake booster (A7/7) is de-energized in the basic position.

The system is ready for braking.

Service brake and ABS function normally.

This mode is also set if there is a fault in the BAS.

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BAS pressure increase

From the speed of the brake pedal, the BAS control unit (N48) recognizes that the preconditions exist for activation of BAS.

The BAS solenoid valve (A7/7y1) is activated by the BAS control unit (N48) and the brake booster produces the maximum brake assistance power.

BAS is activated when the following conditions exist simultaneously:

 Speed > 8 km/h

+ BAS release switch is actuated

+ no current fault is detected.

+ the system is enabled (after self-test)

+ Pedal speed activation threshold exceeded

BAS pressure reduction

The BAS control unit (N48) receives information from the BAS release switch (A7/7s1) that the emergency brake application has terminated. The BAS solenoid valve (A7/7y1) is no longer activated and the maximum braking assistance force is switched off. The normal brake servo assistance remains unchanged.

BAS is switched off when one of the following conditions exists:

 BAS release switch is not actuated

 Speed < 3 km/h

 Duration of activation >20 s

 If no signal from the stop light switch is present after activation of BAS

 A fault is detected that causes the BAS indicator lamp to be activated