BMW 3 SERIES SEDAN 2005 E46 MRSIII Multiple Restraint System Manual

TABLE OF CONTENTS
Subject Page
Multiple Restraint System (MRS III) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
MRS III Control Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Satellite Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Driver’s Front Airbag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Passenger’s Front Airbag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Side Airbags Front/Rear (Thorax) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Head Airbag (ITS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Battery Safety Terminal (BST) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9
Seat Belt Tensioners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Seat Occupancy Sensor (SBE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
MRS III Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
MRS III I-P-O . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Triggering Thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

2
MULTIPLE RESTRAINT SYSTEM (MRS III)
INTRODUCTION
The X5 is equipped with the Multiple Restraint System (MRS III) which employs the use of
“SMART” technology. Smart technology refers to the control module’s programming which
allows for the deployment of the airbags, in stages, depending on the s\
everity of the
impact. Two stage airbags are used for both the driver and front passenger which allows
for a softer cushioning effect when the bags are triggered at lighter impacts.
The MRS III system is installed in E38/E39 and E46 Sedan vehicles as of \
3/99 p roduction
and in E46 Coupes as of 6/99 production.
MRS III control modules are manufactured by either Bosch or Temic. While the functional
operation of both modules are the same. The control modules are not interchangeable from
a replacement standpoint. Always refer to the EPC parts system to ensure that the proper
module is installed in the vehicle.
In addition to the use of two stage airbags for the driver and passenger\
, the following fea-
tures are also included in the MRS III system:
• The MRS III control module is linked to the K-Bus for coding and diagnosis.
• The MRS III includes a fuel pump cut off feature in the event of an airbag deployment.
• Inert gas generators are now used for all air bags and seat belt tensioners.
• The inert gas is a mixtu re of hyd rogen (13.5%) and oxygen (8 6.5%).

3
COMPONENTS
MRS III CONTROL MODULE
The control module is mounted in the center console area on the driveshaft tunnel below
the center storage box. The X5 will use the TEMIC system that can be recognized by the
green 50 pin connector on the module.
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 sen-
sors are installed in the module for crash or impact detection.

4
COMPONENTS
SATELLITE SENSORS
The satellite sensors are mounted below the driver’s and passenger’s front seats on the
seat frame. 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 deter-
mine the deployment of the side/head airbags.
As with the control modules, the satellite sensors
are manufacturer specific. The Temic sensors in
the X5 have a three wire connector which will not
interchange with the Bosch sensors. Only two of
the wires are used for the satellite sensor’s opera-
tion. The signal for deployment of the bags is car-
ried over the power wire of the sensor.

5
COMPONENTS
DRIVER’S FRONT AIRBAG
With the MRS III system, the driver’s front airbag becomes 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 whee\
l as with previ-
ous airbags. The assembly now contains the inert gas generator chamber a\
nd two ignition
stages (ignitors).The airbag consists of:
• Accumulator/gas generator
• Two ignition capsules
• Propellant gas - 13.5% hydrogen/86.5% oxygen
• 64 liter airbag

6
COMPONENTS
PASSENGER’S FRONT AIRBAG
The passenger’s front airbag is the same unit as installed on E38/E39 vehicles as of 9/98
production. The passenger’s airbag consists of:
• Pressure accumulator/gas generator
• Two ignition capsules - for two stage activation
• Propellant gas of - 13.5% hydrogen/86.5% oxygen
• 105 liter airbag
PRESSURE ACCUMULATOR
IGNITION CAPSULES

COMPONENTS
SIDE AIRBAGS FRONT/REAR (THORAX)
The side airbags continue to be mounted in the door panels on the front and rear doors.
Deployment of the side airbags is dependent on the triggering thresholds programmed in
the MRS III control module, based on the inputs from the satellite sensors and internal crash
sensor.
The side airbags use the same cold gas inflation method as the driver’s and passenger’s
front bags.
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8
COMPONENTS
HEAD AIRBAG (ITS)
The head airbags are similar to the ITS bags used on the MRS II system. They continue to be
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 also the cold gas inflation type. The head airbags are always
triggered with the side (Thorax) bags.

COMPONENTS
BATTERY SAFETY TERMINAL (BST)
As with previous systems, the BST is used to disconnect the battery’s “B+” connection to
the engine compartment in the event of an airbag deployment. The safety measure helps
prevents the possibility of a short circuit causing a fire.
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10
COMPONENTS
SEAT BELT TENSIONERS
The seat belt tensioners are a new design
and also make use of the inert gas for trig-
gering. The MRS III control module will
deploy the seat belt tensioners based on
the programmed parameters during impact.
SEAT OCCUPANCY SENSOR (SBE)
The SBE continues to be used as an input to
the MRS III control module for detection of a
front seat passenger. The module uses the
input to determine seat belt tensioner and/or
front airbag deployment.