Deploy supplemental restraint system, function

General function requirements

 Circuit 5R On

Triggering supplemental restraint system (SRS), general

The SRS is continuously monitoring the occupation status of the front passenger seat, the status of the front seat belts (buckled or not buckled) and adjusts its deployment behavior with the help of this information.

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The triggering of the supplemental restraint system is made up of the following partial functions:

 Function sequence for detecting occupied status of front passenger seat

 Function sequence for detecting status of front seat belts

 Impact detection function sequence

 Frontal impact function sequence

 Side impact function sequence

 Rear end collision function sequence

 Rollover function sequence

 Function sequence of additional functions in the event of a crash

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Function sequence for detecting occupied status of front passenger seat

The restraint systems control unit (N2/7) receives the corresponding information from the following components:

- Front passenger seat occupied recognition (B41/1)
(without code (U18) Automatic child seat recognition (ACSR [AKSE]))

- Front passenger seat occupied recognition and automatic child seat recognition (B48)
(with code (U18) Automatic child seat recognition (ACSR [AKSE]))

 Without code (U18) Automatic child seat recognition (ACSR [AKSE]) the status of the seat occupied recognition does not influence the triggering characteristic of the supplemental restraint system.

Function sequence for detecting status of front seat belts

The driver seat belt buckle restraint systems switch (S68/3) or the front passenger seat belt buckle restraint systems switch (S68/4) is actuated by the belt latch which is inserted into the seat belt buckle. This is read in directly by the restraint systems control unit.

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 The status of the rear seat belts does not have any influence on the deployment behavior of the SRS.

Impact detection function sequence

The restraint systems control unit determines the acceleration acting on the vehicle with the aid of its integrated sensor and the following sensors:

- Sidebag and windowbag sensor, left (A53/1)

- Sidebag and windowbag sensor, right (A54/1)

With the aid of this sensor system, the SRS is able to distinguish between the following types of impacts:

- Head-on collision

- Side-on collision

- Rear end collision

- Roll-over

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Frontal impact function sequence

A frontal impact is detected by the restraint systems control unit via the integrated crash sensors.

The restraint equipment is deployed depending on the severity of the impact, the occupation of the front passenger seat, and the status of the front seat belts.

The following squibs can be ignited (at most):

- Driver ETR [GUS] squib (R12/1)

- Passenger ETR squib (R12/2)

- Passenger airbag squib 1 (R12/4)

- Passenger airbag squib 2 (R12/5)

- Left rear ETR squib (R12/6)

- Right rear ETR squib (R12/7)

- Driver airbag squib 1 (R12/13)

- Driver airbag squib 2 (R12/14)

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The following situations are taken into account:

- Occupied state of the front passenger seat:
The restraint systems control unit uses the current occupancy to decide whether to suppress the front passenger airbag unit or to use 1-stage or 2-stage deployment.

- Driver seat belt buckle status:
If the driver seat belt buckle restraint systems switch detects that a belt latch is not inserted into the seat belt buckle, the driver airbag unit with advanced ignition timing is triggered instead of the driver emergency tensioning retractor unit.

- Front passenger seat belt buckle status:
If the front passenger seat belt buckle restraint systems switch detects that a belt latch is not inserted into the seat belt buckle, the front passenger airbag unit with advanced ignition timing is triggered instead of the front passenger emergency tensioning retractor unit.
This only applies, however, if the front passenger seat is known to be occupied. If not occupied then neither the emergency tensioning retractor nor the front passenger airbag unit are triggered.

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Side impact function sequence

A side impact is detected by the restraint systems control unit via the signals from the following components:

- Integrated sensor in the restraint systems control unit

- Left sidebag and windowbag sensor

- Right sidebag and windowbag sensor

The activation of the restraint equipment takes place depending on the severity of the impact and occupation of the front passenger seat.

The following squibs can be ignited (at most):

- Driver ETR [GUS] squib

- Front passenger ETR [GUS] squib

- Left rear ETR squib

- Right rear ETR squib

- Left rear sidebag squib (R12/11)
(with code (293) Left and right rear sidebag)

- Right rear sidebag squib (R12/12)
(with code (293) Left and right rear sidebag)

- Front left sidebag squib (R12/20)

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- Front right side air bag squib (R12/21)

- Left rear windowbag squib (R12/22)

- Right rear windowbag squib (R12/23)

The following state is taken into consideration:

- The restraint systems control unit makes its decision regarding triggering the front passenger sidebag unit based on the current occupancy of the front passenger seat.

Rear end collision function sequence

A rear end collision is detected by the restraint systems control unit via the signals of the integrated sensors.

The activation of the restraint equipment takes place depending on the severity of the impact and the status of the front seat belts.

The following squibs can be ignited (at most):

- Driver ETR [GUS] squib

- Front passenger ETR [GUS] squib

- Left rear ETR squib

- Right rear ETR squib

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The following situations are taken into account:

- Driver seat belt buckle status:
If the driver seat belt buckle restraint systems switch detects that a belt latch is not inserted into the seat belt buckle, the driver emergency tensioning retractor unit is not triggered.

- Front passenger seat belt buckle status:
If the front passenger seat belt buckle restraint systems switch detects that a belt latch is not inserted into the seat belt buckle, the front passenger emergency tensioning retractor unit is not triggered.

Rollover function sequence

A roll-over is detected by the restraint systems control unit via the integrated crash sensors. Only one roll-over around the longitudinal vehicle axis can be detected.

The following squibs can be ignited (at most):

- Driver ETR [GUS] squib

- Front passenger ETR [GUS] squib

- Left rear ETR squib

- Right rear ETR squib

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The following situations are taken into account:

- Driver seat belt buckle status:
If the driver seat belt buckle restraint systems switch detects that a belt latch is not inserted into the seat belt buckle, the driver emergency tensioning retractor unit is not triggered.

- Front passenger seat belt buckle status:
If the front passenger seat belt buckle restraint systems switch detects that a belt latch is not inserted into the seat belt buckle, the front passenger emergency tensioning retractor unit is not triggered.

Function sequence of additional functions in the event of a crash

The additional functions in the event of a crash comprise the following subfunctions:

 Function sequence for activation of hazard warning function

 Function sequence for opening the central locking (CL [ZV])

 Function sequence for shutting off the engine

 Function sequence for shutting off the stationary heater (STH)
(with code (228) Stationary heater)

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Function sequence for activation of hazard warning function

The hazard warning function is activated automatically after a crash event has occurred. The crash signal is sent by the restraint systems control unit over the interior CAN to the rear SAM control unit with fuse and relay module (N10/2). The rear SAM control unit routes the hazard warning flashing function onto the interior CAN by issuing the flasher frequency.

 The turn signal light actuation is described in a separate exterior lights (ABL) document.

Function sequence for opening the central locking (CL [ZV])

The central locking is unlocked automatically after a crash event has occurred. The crash signal is sent by the restraint systems control unit via the interior CAN.

Parallel to the restraint systems control unit a crash event is also detected by a crash sensor integrated into the rear SAM control unit.

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The rear SAM control unit sends the information via the interior CAN.

The following central locking motors are then actuated as follows:

- from the left front door control unit (N69/1) of the left front door central locking motor (M14/6)

- from the right front door control unit (N69/2) of the right front door central locking motor (M14/5)

 The central locking is unlocked after a waiting time of t = 8 to 11 s expires.

Function sequence for shutting off the engine

The engine is shut off automatically after a crash event has occurred. The crash signal is sent by the restraint systems control unit over the interior CAN to the EIS [EZS] control unit (N73). This sends the crash signal over the engine compartment CAN to the CDI control unit (N3/9) (with diesel engine) or to the ME-SFI [ME] control unit (N3/10) (with gasoline engine), which then causes the engine to be switched off.

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Function sequence for shutting off the stationary heater (STH)

The STH is shut off automatically after a crash event has occurred. The crash signal is sent by the restraint systems control unit over the interior CAN to the stationary heater control unit (A6n1), which then switches off the stationary heater.

The shutoff process can only be reset using STAR DIAGNOSIS.