Part II

Crash Safety

Functional networking
The following graphic illustrates the operating networks of the safety systems in the Europe and in the US versions using the example F25.










The following graphic illustrates the operating networks of the safety systems in the Europe and in the US versions using the example F06, F12, and F13 .










The following graphic illustrates the operating networks of the safety systems in the Europe and in the US versions using the example F30.










Self-test
In addition to all the inputs and outputs, the Crash Safety Module (ACSM) also monitors the internal components (self-test). Possible fault codes are stored in the Crash Safety Module. In the event of a system error or a fault in a component, the airbag warning lamp lights up.
The Crash Safety Module performs a self test after the ignition is switched on. The airbag indicator lamp in the instrument cluster remains on during this period (of roughly 3 to 5 seconds). The airbag indicator lamp goes out as soon as the safety system is ready for operation.
If the instrument cluster fails to receive a CAN message from the Crash Safety Module in this period the airbag indicator lamp will light up.
The airbag indicator light remains on if the Crash Safety Module detects an existing fault or one that has been stored during the self-test or while driving.
If a fault is detected in the safety system, the operability of the safety system is partially maintained under the following conditions:
- If a fault is detected in a circuit of the safety system, only the function of the circuit concerned is disabled. The other airbag and seatbelt tensioners remain functional.
- In the event of a fault in the circuit of the airbag warning lamp, the lamp does not light up in the self-test.
With the precondition that no other fault is present, the safety system remains functional without restriction.

In the event of an internal malfunction or a fault in the power supply in the Crash Safety Module, the entire safety system will be disabled (airbag indicator and seat belt warning lamps light up, Check Control message in the instrument cluster).

Impact detection
The Crash Safety Module (ACSM) detects all impacts throughout a 360° range.
Within the Crash Safety Module the direction and severity of the impact are determined based on inputs from the following external sensors:
- Front airbag sensor on left and front airbag sensor on right (note national version)
- Airbag sensor for left front door and airbag sensor for right front door (note national-market version)
- Left B-pillar airbag sensor and right B-pillar airbag sensor
- Longitudinal acceleration sensor and lateral acceleration sensor for impact recognition in the ICM control unit
- Vertical acceleration sensor in the ICM control unit (note vehicle equipment level and national-market version)
- Yaw rate sensor in the ICM control unit (note vehicle equipment and national-market version)
The Crash Safety Module processes all acceleration data. This determines the direction of a collision and the severity of the accident.

Activating the safety system
Comprehensive tests are used to define triggering thresholds for all possible types of accident. This results in different trigger thresholds for activation of the various restraint systems (airbags, seatbelt tensioners, etc.). The restraint systems are only triggered if 2 independent sensors simultaneously detect the corresponding threshold values.
The Crash Safety Module (ACSM) processes acceleration data from the sensors. The Crash Safety Module relies on acceleration data to determine the direction and severity of an impact. In the event of an impact the Safety Module determines whether deployment is required and which gas generators (belt tensioner, airbags, etc.) should be ignited. For example, the seatbelt tensioners have a lower trigger threshold than the front airbags. This means that depending on accident severity, only the belt tensioner may be activated by the Crash Safety Module.

Message to other control units
The Crash Safety Module (ACSM) transmits a message to other devices on the bus when the restraint systems are triggered. Depending upon accident severity the responsible control units can carry out functions such as the following:
- Switching off the electric fuel pump (via DME control unit)
- Switching off the alternator (via DME control unit)
- Opening the central-locking system (via the junction box electronics)
- Switching on the interior lights (via the footwell module)
- Switching on the hazard warning lights (via the footwell module)

Visual and acoustic seat belt warning for driver belt and passenger belt
For the seat belt warning, the signals of the 2 belt buckle switches (driver belt, passenger belt) are monitored separately. If the seat occupancy detection indicates that the front passenger seat is occupied, the passenger belt must also be inserted in the belt buckle. The seat belt warning then goes out.
The following situations are taken into account for output of a seat belt warning:
- Front seat belt not fastened and distance driven less than 200 m
With a driven distance below 200 m, only a visual seat belt warning is displayed (the seat belt warning lamp lights up). The vehicle can e.g. be driven out of the garage without triggering an acoustic seat belt warning.

- Front seat belt not fastened and distance travelled more than 200 m
The seat belt warning lamp lights up (visual seat belt warning). The acoustic seat belt warning is switched on for approx. 90 seconds. Once the seat belt has been fastened, the visual seat belt warning disappears. The acoustic seat belt warning is switched off. If the seat belt has not been fastened by the end of the audible seat belt warning, the seat belt indicator light lights up.

- Unfastening the front seat belt when the vehicle is in motion
If a belt buckle is opened while the vehicle is being driven, the seat belt warning lamp lights up immediately. A brief acoustic warning signal sounds. After approx. 15 seconds, an additional acoustic seat belt warning is switched on for approx. 90 seconds. Once the seat belt has been fastened, the visual seat belt warning disappears. The acoustic seat belt warning is switched off. If the seat belt has not been fastened by the end of the audible seat belt warning, the seat belt indicator light lights up.

Notes for Service department

General notes
The following general instructions have been issued for servicing the safety system:

NB: After disconnecting the battery terminals, wait 1 minute before starting work on the safety system.
Following disconnection of the battery terminals, personnel must allow at least one minute to elapse before starting work on the safety system. The waiting period ensures that the capacitors with the energy reserve of the system are completely discharged. This prevents inadvertent triggering of airbags or seatbelt tensioners.

NB: Install only officially-approved seat covers
Never install seat covers, seat cushions or other objects on the front seats unless they have been specifically approved for seats with integral side airbags. Do not hang articles of clothing, e.g. jackets, over the front seat backrests. This severely impairs or disables the airbag function.

Diagnosis instructions

NOTE: Replace the Crash Safety Module after 3 crash signals followed by deployment of the safety system

When the safety system is triggered, the crash safety module stores data in a non-erasable memory. The data is relevant to accident research (no access for service). After 3 crash signals, the data memory is full. The airbag warning lamp lights up. The Crash Safety Module must be replaced.

Notes on encoding/programming

NOTE: Deactivating the acoustic seat belt warning

The acoustic seat-belt warning can be deactivated by encoding. This does not affect a legally prescribed seat belt warning.

NOTE: Code crash safety module

Following replacement the Crash Safety Module must be encoded.

National-market versions

National-market version for US
2-stage driver's airbag and front passenger airbag with pyrotechnically activated discharge hole The driver's airbag and front passenger airbag are each equipped with a 2-stage gas generator. The discharge hole in the airbag serves to adapt the hardness of the airbag in an optimal way in the event of an accident. The discharge hole is pyrotechnically activated. Depending on the accident severity, both stages of the airbag as well as the ignition squib for opening the discharge hole are activated with a time delay. This enables adaptation of the restraint function of the airbag to the severity of each accident, thus minimising the additional load on the occupants during the unfolding phase of the airbag.

Visual and audible seat belt warning
As of terminal 15 On, a visual and acoustic seat belt warning is issued. The seat belt warning has a time limit (6 seconds).
The further progression of the seat belt warning is identical to that of the seat belt warning in Europe vehicles.

Enable seat occupancy mat
Following replacement of the seat-occupancy mat with capacitive sensor system, the seat-occupancy mat must be enabled. A service function is available for initialization.

National version Japan / Gulf states

Visual and audible seat belt warning
As of terminal 15 On, a visual and acoustic seat belt warning is issued. The seat belt warning has a time limit (6 seconds).
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.