Part II

Multiple Restraint System (MRS)

System functions
The following system functions are described for the multiple restraint system:
- Self test
- Collision detection
- Activating the safety system
- Data storage on activation of the safety system
- Message to other control units
- Visual and acoustic seat belt warning

Self test
In addition to all inputs and outputs, the MRS control unit also monitors the internal components (self-test).
Possible faults are stored in the MRS control unit. In the event of a system error or a fault in a component, the airbag warning lamp lights up.
The MRS control unit starts a self-test after the ignition has been switched on. During this time, the airbag warning lamp lights up (approx. 3 to 5 seconds). When the safety system is functional, the airbag warning lamp goes out. If the instrument cluster receives no CAN message from the MRS control unit, the airbag warning lamp lights up. If the MRS control unit has already detected a current or stored fault during the self-test or while the vehicle is being driven, the airbag warning lamp remains switched on.

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 selftest. With the precondition that no other fault is present, the safety system remains functional without restriction.

In the event of an internal fault in the MRS control unit or power supply, the entire safety system is disabled (airbag warning and seat belt warning lamp light up, Check Control symbol in the LC display)

Collision detection
The MRS control unit picks up every collision within an angular range of 360°.
The direction and severity of a collision are picked up by acceleration sensors in the MRS control unit and by external acceleration sensors.

External acceleration sensors:
- Front airbag sensor for driver and front airbag sensor for passenger (bear the national version in mind)
- Front door airbag sensor on driver's side and front door airbag sensor on passenger's side (bear the national version in mind)
- Airbag sensor on driver's side B-pillar and passenger's side B-pillar

The MRS control unit processes all the acceleration data. This determines the severity of the accident.







Activating the safety system
Comprehensive tests are used to set trigger thresholds for all possible types of accident.
These result in different trigger thresholds for activation of the following restraint systems (bear the national version in mind):
- Belt tensioner
- Front airbags
- Side airbags
- Head airbags







The restraint systems are only triggered if 2 independent sensors simultaneously detect the corresponding threshold values.
For example, a frontal collision is detected via the longitudinal acceleration sensor in the B-pillar airbag sensor on the driver's side and the longitudinal acceleration sensor in the MRS control unit.
The MRS control unit uses the data sent by the sensors to calculate the direction of the collision and the severity of the accident. Depending on the severity of the accident, the electric fuel pump is switched off.

Two examples (frontal collision and side-on collision) are used to illustrate the triggering of the various restraint systems:
- Frontal collision
The restraint systems (seatbelt tensioners, front airbags) are triggered when a frontal collision is so strong that the trigger threshold in the MRS control unit is exceeded.
The seatbelt tensioners have a lower trigger threshold than the front airbags. This means that, depending on the severity of the accident, only the seatbelt tensioners are triggered by the MRS control unit.
If the belt buckle switch is defective, the MRS control unit attempts to trigger the seatbelt tensioner despite the fault signal.
Depending on the severity of the accident, the electric fuel pump is switched off.
- Side-on crash
If the trigger threshold in the MRS control unit is exceeded, the side airbag and head airbag on the side affected by the collision are triggered (bear the national version in mind).
Depending on the severity of the accident, the electric fuel pump is switched off.

Data storage on activation of the safety system
When the restraint systems are triggered, certain data is written into a non-erasable data memory of the MRS control unit. The data is relevant to accident research (no access for service).

Message to other control units
If the restraint systems trigger, the MRS control unit sends a message to other control units. Depending on the severity of the accident, the relevant control units perform the following functions:
- Switching off the electric fuel pump (via the digital engine electronics control unit)
- Switching off the alternator (via the digital engine electronics 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 occupation detection indicates that the passenger's 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 travelled below 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 above 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.
When the seat belt is fastened, the visual seat belt warning goes out. The acoustic seat belt warning is switched off.
If the seat belt is not fastened after the acoustic seat belt warning has timed out, the seat belt warning lamp lights up.
- Front seat belt unfastened while the vehicle is being driven
If a belt buckle is opened while the vehicle is being driven, the seat belt warning lamp lights up immediately.
After approx. 15 seconds, an additional acoustic seat belt warning is switched on for approx. 90 seconds.
When the seat belt is fastened, the visual seat belt warning goes out. The acoustic seat belt warning is switched off.
If the seat belt is not fastened after the acoustic seat belt warning has timed out, the seat belt warning lamp lights up.

Visual seat belt warning for seat belt, rear left and rear right (only EURO version)


Only R56
For the visual seat belt warning, the status signals of the 2 belt buckle switches (rear left and rear right seat belts) are monitored separately (bear national version in mind).
The status display or visual seat belt warning (seat belt fastened or not fastened, as the case may be) is displayed in the LC display of the instrument cluster separately for each seat belt.







The visual seat belt warning starts directly after the service requirement display, at the latest 5 seconds after terminal 15 On. The visual seat belt warning is switched on for 30 seconds.
With every change in state, the display duration (30 seconds) starts anew. Change in state i.e.:
- Seat belt is fastened at terminal 15 On
- Seat belt is unfastened at terminal 15 On
- Engine is started during the status display for the seat belt
- Engine is started after the status display for the seat belt
- Seat belt is unfastened at engine On

The display can be cancelled at any time by briefly pressing the onboard computer button.

Notes for Service department

General information
The following general data is provided for servicing the MRS:
- Disconnecting the battery terminals
- Checking the components of the multiple restraint system
- Fitting approved seat covers

Disconnecting the battery terminals

NB: After disconnecting the battery terminals, wait 1 minute before starting work on the MRS safety system.

After disconnecting the battery terminals, 1 minute must be waited before starting work on the MRS 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.

Checking the components of the multiple restraint system

NB: Do not test components of the safety system with multimeters or other universal test devices.

Testing with a multimeter or other universal test tools can lead to accidental deployment and injuries. For system diagnosis, use only the BMW diagnosis system.

NB: Do not connect any electrical test devices to the wire harness of the multiple restraint system.

Do not connect any electrical test devices to the wire harness of the multiple restraint system as long as the wire harness is connected to a component of the safety system. Accidental deployment and violation can occur. Use exclusively the BMW diagnosis system for system diagnosis.

NB: Check the safety system MRS after repairing damage caused by an accident.

After repairing damage caused by an accident, the MRS safety system must be checked using the BMW diagnosis system (even if this accident did not trigger a restraint system).

Fitting approved seat covers

NB: only fit approved seat covers.

Do not fit seat covers, cushions or other objects on the front seats that have not been specially approved for seats with integrated 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: After 3 crash signals with triggering of the safety system, replace the MRS control unit.

The MRS control unit stores data in a non-erasable memory after a triggering of the safety system. After 3 crash signals, the data memory is full. The airbag warning lamp lights up. The MRS control unit must be replaced.

Notes on coding / 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.

National versions

National version US

2-stage driver's airbag and passenger's airbag
The driver's and passenger's airbag are each equipped with a 2-stage inflator assembly. Depending on the severity of the accident, the two level of the airbag are triggered with a delay.
The two stages of the inflator assembly enable a restraint function that is adapted the severity of each accident and prevents additional load on the occupants during the unfolding phase of the airbag.

Front airbag sensor, driver's side and front-passenger side
The 2 front airbag sensors are longitudinal acceleration sensors. The sensors in the front on the left and right detect a frontal or rear-end collision.

Seatbelt tensioners for driver belt and passenger belt

R55 as of volume production launch
R56 as of 12/2007

The seatbelt tensioner for the driver's seat belt and the seatbelt tensioner for the passenger belt also trigger in the event of a side-on crash.

Seat occupation mat, passenger
The passenger seat occupation detection detects whether the seat is occupied or not.
The seat occupation mat consists of conductor tracks with pressure sensors. The conductor tracks are connected to the electronic evaluation unit.
If the seat occupation mat is defective, the airbags on the passenger's side are automatically disabled (passenger's airbag and side airbag). The indicator lamp for the passenger's airbag deactivation lights up.







According to the regulations of the NHTSA (National Highway Traffic Safety Administration), a small child in the child restraint system specifically designed for the purpose on the front passenger's seat must be detected automatically.
On detection, the airbags on the passenger's side are automatically disabled (front passenger's airbag and side airbag). The indicator lamp for the passenger's airbag deactivation lights up.







If a person of adequate size sitting correctly (adolescent / adult) is detected, the airbag on the passenger's side are activated (passenger's airbag and side airbag). The indicator lamp for the passenger's airbag deactivation does not light up.
In certain cases involving adolescents and adults, the front passenger's airbag can deactivate (indicator lamp for front passenger's airbag deactivation lights up). In these cases, the seat position must be can be changed until the indicator lamp for the front passenger's airbag deactivation goes out (front passenger's airbag and side airbag activated).
The seat occupation detection is based on evaluation of the applied surface pressure that is created when a load is applied. The distances of the surfaces and centres of gravity on the occupied seat cushion indicate whether an adolescent or adult or small child is in the child restraint system specifically designed for the purpose.







Seating position sensor
According to the regulations of the FMVSS (Federal Motor Vehicle Safety Standard), a 5 %- woman must be distinguished from a 50 % man on the driver's seat.
The seating position sensor detects the airbag range designed for a person with regard to the seat adjustment in longitudinal direction.







The seating position sensor is a Hall sensor and it is supplied with voltage via the MRS control unit. The current intensity changes depending on the distance of the seat position switch to the magnet holder.







The signal of the seating position sensor also influences the delayed triggering of stage 2 of the inflator assembly (driver's airbag).

Visual and acoustic 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 rest of the sequence for seat belt warning is identical to the seat belt warning in EURO vehicles.

National version Japan / Gulf states

Visual and acoustic 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).

No liability can be accepted for printing or other errors. Subject to changes of a technical nature