Brief description of components: Notes

The following sensors detect the direction and severity of an impact:

• Acceleration sensors in the MRS control unit 

  There is a lateral acceleration sensor and a longitudinal acceleration sensor in the MRS control unit. The sensors are arranged at 90 degrees to each other.

• Airbag sensors on left-hand B-pillar and right-hand B-pillar 

  Each of the airbag sensors on the B-pillars contains a lateral-acceleration sensor and a longitudinal-acceleration sensor. The sensors are arranged at 90 degrees to each other.

  For more information, refer to R50, R52, R53 - AIRBAG SENSORS ON LEFT-HAND B-PILLAR AND RIGHT-HAND B-PILLAR  .

• Front airbag sensors 

  The 2 front airbag sensors are longitudinal acceleration sensors.

  For more information, refer to R50, R52, R53 FRONT AIRBAG SENSORS   .

• Airbag sensors on front left door and front right door 

  The 2 airbag sensors are pressure sensors.

  For more information, refer to R50, R52, R53 - AIRBAG SENSORS ON FRONT LEFT DOOR AND FRONT RIGHT DOOR  .

  The following components provide additional input signals for the multiple restraint system:

• Passenger seat occupancy detector 

  Statutory guidelines in the USA stipulate that the seat occupancy detector mat integrated into the front-passenger seat must be able to recognize a child seated in a rearward-facing child seat. Upon detection, the airbags on the passenger side are automatically deactivated (passenger airbag and side airbag). The indicator lamp for passenger airbag deactivation lights up.

  The seat-occupancy detector evaluates the impression caused from a load on the seat.

  If the multiple restraint system (MRS) triggers the airbags and the front-passenger seat is unoccupied, the front-passenger airbag and the side airbag on the front-passenger side will not be triggered.

  The head-level airbag will still be triggered.

  For more information, refer to R50, R52, R53 - SEAT-OCCUPANCY DETECTOR, PASSENGER  .

• Seat-belt buckle switch for driver's seat and front-passenger seat 

  The MRS control unit uses the signals from the driver's seat-belt buckle switch and the front-passenger seat-belt buckle switch to detect whether or not the seat belts are fastened.

  If the seat belt is fastened, the seat-belt tensioner will also be triggered (only in the event of frontal impact or a rear-end collision).

  The following control units are involved in the function of the MRS:

• MRS control unit 

  All triggering circuits and sensors in the multiple restraint system (MRS) are connected directly to the MRS control unit.

  The MRS control unit evaluates the data it receives from the sensors. In the event of a collision (head-on, rear-end or side impact), the MRS control unit will decide whether the seat-belt tensioners and airbags need to be triggered, and which airbags need to be triggered.

  For more information, refer to R50, R52, R53 - MRS CONTROL UNIT  .

• DME: Digital engine electronics 

  Depending on accident severity, the electric fuel pump will be switched off by the DME.

  Signal path: MRS control unit -> K-bus -> General module -> K-bus -> Instrument cluster -> PT-CAN -> DME -> Direct wire -> Fuel-pump relay -> Electric fuel pump

• Instrument cluster 

  The instrument cluster generates the optical and audible seat-belt warning.

  When terminal R is ON, the instrument cluster receives the status message from the MRS control unit via the K-bus. Depending on the status, the optical and audible warning is triggered when terminal 15 is ON.

• GM: General module 

  The general module is connected to the MRS control unit via the K-bus.

  The general module is the executing control unit for the central locking system. The general module also controls the interior and exterior lighting.

  Depending on severity, the central locking is unlocked in the event of an accident. The interior lights and the hazard warning lights are automatically switched on.

  Signal path: MRS control unit -> K-bus -> General module

  The following components are activated by the MRS control unit:

• Multiple restraint system triggering circuits 

  With maximum equipment, the MRS (multiple restraint system) comprises the following triggering circuits:

  • Driver's airbag (stage 1)
  • Front-passenger airbag (stage 1)
  • Driver's airbag (stage 2)
  • Front-passenger airbag (stage 2)
  • Side airbag in driver's seat
  • Side airbag in front-passenger seat
  • Head-level airbag, left (optional)
  • Head-level airbag, right (optional)
  • Belt tensioner, front left
  • Belt tensioner, front right
  • Safety battery terminal

  Driver and front-passenger airbag 

  The driver and front-passenger airbag reduce the risk of injury to the occupants' head and chest area in the event of a head-on collision.

  The driver airbag is located under the center pad on the steering wheel. The front-passenger airbag is integrated into the instrument panel above the glove compartment.

  Side airbag 

  The side airbags are located in the side sections of the front-seat backrests.

  The relocation into the backrest side section has the advantage that there are no longer airbags in the doors, allowing the engineers more freedom when designing the doors.

  Both versions, airbags in doors and airbags in seats, satisfy the strict legal requirements with regard to occupant safety to the same degree.

  Side airbags reduce the risk of injury to the pelvis and torso of the driver and front passenger's in the event of a side impact.

  For more information, refer to R50, R52, R53 - SIDE AIRBAG  .

  Head-level airbag 

  The head-level airbag prevents the head making direct contact with the side structure or an object which penetrates the vehicle. The head-level airbag thus reduces the risk of head injuries for vehicle occupants. (the head-level airbag is optional.)

  For more information, refer to R50, R53 - HEAD-LEVEL AIRBAGS  .

  Belt tensioners 

  As a rule, the seat belt will not be sitting completely tight around the body: This seat belt slack makes sure that the occupants have adequate comfort of movement.

  To prevent the negative effect that this loose belt can have, the pyrotechnic seat-belt tensioner will pull the belt buckle down by several centimeters in the event of a frontal or rear-end collision. This pulls the seat belt tight into the occupant's shoulder and pelvis.

  Safety battery terminal 

  Depending on the severity of the accident, the safety battery terminal disconnects the starter motor and the alternator from the battery. (only diesel vehicles and R53.) This minimizes the risk of short circuits in a serious accident. The trigger signal comes from the MRS control unit.

• Airbag warning lamp 

  The airbag warning lamp shows the operational capability of the multiple restraint system (MRS). The airbag indicator lamp in the instrument cluster is activated by the MRS control unit (via the K-bus).

  After the ignition is switched on, the MRS performs a self test. During this time, the airbag indicator lamp will light up (approximately 3 to 5 seconds). When the system is ready for operation, the airbag indicator lamp goes out.

  If the instrument cluster has not received a bus signal, the airbag indicator lamp will light up.

  If, during the self test or while the vehicle is in motion, the MRS control unit detects an existing fault or one that has been stored, the airbag warning lamp remains on.

  If the MRS detects a fault, the operational capability is partially maintained, subject to the following:

  • If a fault is detected in an MRS circuit, only the affected circuit is deactivated. The other airbags and belt tensioners remain operational.
  • If there is a fault in the airbag warning lamp circuit, the lamp does not light up during the self-test. If there is no other fault, the MRS remains fully operational.

  If there is an internal fault in the MRS control unit or in the power supply, the entire system is deactivated. (airbag and seat belt warning lights come on)

• Seat-belt indicator lamp 

  The seat-belt indicator lamp is the visual seat-belt warning. The visual seat-belt warning instructs the front-seat occupants to fasten their seat belts. Terminal 15 ON activates the visual seat-belt warning.

  The visual seat-belt warning is issued as follows:

  • Seat-belt indicator lamp in the instrument cluster (required by law)
• Indicator lamp for front-passenger airbag deactivation 

  After the ignition is switched on, the MRS performs a self test. In this time, the warning lamp for passenger-airbag deactivation lights up (approx. 3 to 5 seconds). The status of the airbags on the passenger side (passenger airbag and side airbag) is then displayed.

  If the warning lamp for passenger-airbag deactivation ("Passenger Airbag OFF" lamp) is lit, the following airbags on the (occupied) passenger side have been deactivated: front-passenger airbag and side airbag.

  The "Passenger Airbag OFF" lamp is constantly monitored by the MRS control unit. A fault in the power supply or a defective lamp is stored in the MRS control unit's fault memory. If this occurs, the airbag warning lamp is switched on. "Passenger Airbag OFF" lamp installation location

  R50/R53: roof console

  R52: cowl panel

• Electric fuel pump cutoff 

  Depending on accident severity, the fuel supply may also be cut off.

  Signal path: MRS control unit -> K-bus -> General module -> K-bus -> Instrument cluster -> PT-CAN -> DME -> Fuel-pump relay -> Electric fuel pump

  Mechanical components in the multiple restraint system (MRS):

• Belt force limiters on seat belts 

  The seat belts are the primary restraint system for all occupants. Each of the 4 seats is fitted with a lap and diagonal automatic belt.

  To minimize the load on the chest area of the front passengers in the event of a severe head-on collision, the front seat belts are fitted with belt force limiters as standard. The belt force limiters ensure that the belt strap can give slightly if the load exceeds a certain level. The risk of injury due to the belt force acting on the body is thus reduced.

• Knee protection 

  An additional impact protection is fitted in the area of the knees on the driver's and front-passenger side. This knee protection provides extensive support for the knees in the event of an accident. The knee protection reduces the load on the lower extremities, especially if the front occupants are not wearing their seat belts.

  At the same time, a controlled forward movement of the upper body towards the relevant airbag (driver or passenger airbag) is initiated.