Overall Function

NOTE: For model name/model number cross reference refer to Model Designation Table. Application and ID






General
The corresponding functions in the Brake Assist (BAS) brake booster(A717) are controlled by the electrical/electronic components.

On model 168 the voltage is supplied to the BAS control module (N48) via the fuse and relay box (F1), on models 129 and 140 via the base module (N16/1) and on models 163, 170, 202, 208, 210 and 220 via the relay module (K40).

On all vehicles with engines 112, 113 (on model 210 with engine 606 as well) and Electronic Stability Program (ESP), the BAS control module function is integrated in the ESP control module (N47-5). On models 163, 168 and 220 the BAS control module function is integrated in the ESP control module (N47-5).

The BAS control module receives input signals from the following components:
- Engine Control Module (ME-SFI) (via Controller Area Network (CAN) data bus)
- Traction systems control module (via CAN data bus)
- BAS diaphragm travel sensor
- BAS release switch

The input signals are processed into output signals in the BAS control module for the following components:
- BAS solenoid valve
- BAS malfunction indicator lamp (via CAN data bus)

Based on the input signals, the BAS control module (N48) or ESP control module (N47-5) decides which of the following 3 operating modes have to be actuated
- Normal mode
- BAS pressure build-up
- BAS pressure reduction.

Normal Mode
In this case there is no braking with correspondingly high pedal speed (which requires switching on BAS). The solenoid valve in the BAS brake booster (N47-5) is de-energized in the initial position.

The system is ready for braking.
Service brake and ABS function normally.

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

BAS Pressure Build-Up
From the speed the brake pedal is operated and vehicle speed, the BAS control module (N48) recognizes that the conditions for switching on BAS exist.
The BAS solenoid valve (A7/7y1) is actuated by the BAS control module (N48) and the brake booster produces the maximum brake boost.

BAS is switched on when the following conditions occur at the same time:

- Vehicle speed greater than 8 km/h
BAS release switch actuated
No current fault recognized
The system is enabled (after self-test)
Switch-on threshold of pedal speed exceeded

BAS Pressure Reduction
The BAS control module (N48) receives the information that emergency braking is complete from the BAS release switch W/7sl). The BAS solenoid valve (A7/7y 1) is no longer actuated and maximum brake boost is switched off. The normal brake boost.

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

BAS Release Switch Is Not Actuated
- Vehicle speed less than 3 km/h
- Switch on duration greater than 20 seconds
- If there is no signal from the stop lamp switch after BAS is switched on
- A fault is recognized which results in actuation of the BAS malfunction indicator lamp.