Components

COMPONENTS

MRS III Control module
The control module is mounted in the center of the vehicle on the driveshaft tunnel below the center console. The control module contains the processing electronics (Smart Technology) for triggering of all air bags and pyrotechnic devices installed in the vehicle. Two electronic deceleration sensors are installed in the module for crash or impact detection.

The system is recognized by the 50 pin connector on the control module. There are two manufactures of MRS III systems: Bosch and Temic. Definitive verification of the installed system is carried out through the identification pages of the diagnostic testers.

The MRS III is connected to the K-bus (except Z3).




Satellite Sensors







The satellite sensors are mounted below the driver's and passenger's front seats on the vehicle floor pan. The function of the sensors is to detect the severity of side impacts and signal the MRS III control module, through a pulse modulated signal, in the event of a crash. The control module uses this input signal along with its internal impact sensor signal to determine the deployment of the side/head airbags.




The satellite sensors of the MRS III use only two wires over the previous three wire sensors of the MRS II. The signal is received by the MRS III control unit over the reference voltage supply wire.

As with the control modules, the satellite sensors are manufacturer specific. The Temic sensors will not interchange with the Bosch sensors.

Driver's front air bag
The driver's front airbag is a two stage bag similar to the passenger's front side bag, introduced on the 1999 model E38/E39s. The complete assembly is mounted beneath the cover in the center of the steering wheel as with previous airbags. The assembly contains the inert gas generator chamber and two ignition stages (ignitors).






The airbag consists of:
- Accumulator/gas generator
- Two ignition capsules
- Propellant gas - 13.5% Hydrogen/86.5% Oxygen

Passenger's front air bag
The passenger's front airbag is mounted in the dashboard above the glove box.






The airbag consists of:
- Pressure accumulator/gas generator
- Two ignition capsules - for two stage activation
- Propellant gas of - 13.5% hydrogen/86.5% oxygen

Side air bags front and rear (thorax)






The side airbags are mounted on the inner door frame of the front and rear doors. Deployment of the side airbags is dependent on the triggering thresholds programmed in the MRS III control module and based on the inputs from the satellite sensors and internal crash sensors.

The side airbags use the same cold gas inflation method as the driver's and passenger's front bags.

Rear side airbags arrive de-activated from the factory and can only be enabled upon written customer request. This is designed to prevent a risk of injury to small children who may be sitting out of position and too close to an airbag in the back seat.

Front Head protection air bags (Inflatable Tubular Structure. ITS)






The head airbags are similar to the ITS bags used on the MRS II system They are mounted from the "A" pillar up along the headliner and are anchored behind the "B"pillar. The ITS bags of the MRS III system are the cold gas inflation type. The head protection airbags are always triggered along with the front side (thorax) bags.

E38 and E39 Rear Head Protection System
Rear Head protection is available on E38 and E39 sedans ordered with optional rear side airbags.




The airbags are a cushion (not an ITS) that is deployed from behind the C-pillar trim. The HPS will not be de-activated along with the side airbags from the factory since there is no danger to small children sitting out of position.

A vehicle with rear HPS can be identified by observing "HPS" embossed in the C-pillar cover.

Battery Safety Terminal (BST)




The BST is used to disconnect the battery connection to the starter, alternator and charging post in the event of a collision. This safety measure helps prevents the possibility of a short circuit in the engine compartment causing a fire.

The battery connection to the power distribution box and body electronics is un-affected.

Seat Belt Tensioners




The seat belt tensioners also make use of the inert gas for triggering. The MRS III control module will deploy the seat belt tensioners based on the programmed parameters during a collision.

Seat Occupancy Sensor (SBE)




The SBE is used as an input to the MRS III control module for detection of a passenger in the right front seat. The MRS III uses the input to determine seat belt tensioner and/or front airbag deployment thresholds.