BAS Control Module

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

Function





On all vehicles with engine 112 or 113 and electronic Stability Program (ESP) and on model 210 additionally with engine 606 and ESP, the Brake Assist (BAS) function is integrated in the ESP control module (N47-5).
On models 163, 168 and 220 the BAS function is integrated in the ESP control module (N47-5).

The BAS control module (N48) is divided up functionally as follows:
- Signal conditioning
- Logic section
- Safety circuit

Signal Conditioning
The following input signals are conditioned for the logic section:
- 2 front speed sensors (via Controller Area Network (CAN) from traction systems control module: Anti-Lock Brake System (ABS), Electronic Traction System (ETS), Acceleration Slip Regulation (ASR) or ESP)
- Stop lamp switch (via CAN from traction system control module: ABS, ETS, ASR or ESP)
- Vehicle identification (vehicle model and engine from the respective engine control module via CAN)
- BAS diaphragm travel sensor
- BAS release switch

Logic Section
The initialization and the safety check of the system starts after the ignition is switched on. The system is enabled after a positive response.
The conditioned input signals are processed in the logic section and the following values calculated
- Vehicle speed from the front wheel speed signals
- Vehicle acceleration from several wheel speeds measured in sequence.
- Diaphragm speed: The control module checks the voltage signal from the diaphragm travel sensor every 3 ms. The pedal speed is calculated from the voltage difference between two sequential measurements.
- Learning algorithm: Calculation of vehicle deceleration to adapt the triggering threshold to the different conditions of the brake system
- Connection threshold: it is calculated from the basic threshold (vehicle identification values), vehicle speed, brake pedal speed and the learning algorithm values.

If the values determined exceed the specified connection threshold, a BAS connection is initiated.

The BAS connection is terminated immediately after a signal fram the BAS release switch

Safety Circuit
The task of the safety circuit is to recognize faulty signals in the control module and faults in the electrical cable system.

The following components are monitored constantly:
- BAS solenoid valve (A7/7y1)
- BAS diaphragm travel sensor (A7/7b1)
- BAS release switch (A7/7s1)
- Stop lamp switch (4-pin) (S9/1).

The system switches off if a fault is recognized. This is displayed to the driver by the malfunction indicator lamp coming on:
- BAS, BAS/ETS, BAS/ASR or BAS/ESP (A1e39, e49, e48 or e47) malfunction indicator lamp.
- On model 220 by the multi-function display (A1p13).

A fault code is also stored in the control module.

Furthermore the safety circuit continuously monitors battery voltage. If the voltage drops below 10 V or exceeds 16-18 V, the system is also switched off until the voltage is back in the specified range.