belt 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

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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%).

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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.

MRS III OPERATION
As with previous systems, the triggering thresholds are programmed in the MRS III control
module. These thresholds are determined by BMW through crash and vehicle testing dur-
ing the design and development of the vehicle. These thresholds will vary depending on the
vehicle size and design.
There are several different thresholds for airbag and safety restraint deployment including;
• Belt pre-tensioner threshold for activation of the seat belt tensioners.
• Airbag threshold #1 - the first level of activation for the two stage front airbags, always
deployed first when the front triggering threshold is reached.
• Airbag threshold #2 - the second level of the two stage front airbags, can be deployed
simultaneously or after a time delay, depending on the severity of the impact.
• Rear crash threshold - for activation of the seatbelt tensioners with a rear impact.
• Battery safety terminal threshold - for activation of the BST with airbag deployment.
• Side airbag/ITS threshold - for deployment of the side and thorax airbags.
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If the signal from the SBE is defective on triggering, the MRS III will deploy as if the seat is
occupied.
If the signal from the seat belt contacts are defective, the MRS III will deploy as if the belts
were not buckled.
MRS III OPERATION
TRIGGERING THRESHOLDS - TWO STAGE AIRBAGS
The programming of the MRS III includes four triggering thresholds for the two stage front
airbags. The triggering of the front airbags is also dependent on whether the seat belts are
connected and if the front passenger seat is occupied. The triggering thresholds for the
two stage airbags are as follows:

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TRIGGERING THRESHOLDS
SIDE AIRBAGS/ITS
The triggering thresholds for the side airbags/ITS is dependent on the signals from the
satellite sensors and the crash sensor in the MRS III control module. The triggering thresh-
olds are independent of the belt tensioners.
BELT TENSIONER
The triggering of the belt tensioners is dependent on the signal from the seat belt contact
and the severity of the impact as detected by the control module.
BATTERY SAFETY TERMINAL
The BST will deploy in a frontal impact at threshold 2 or greater. The threshold for BST acti-
vation with a side impact is programmed separately in the side deployment criteria. The
BST will also be deployed when the rear impact threshold is exceeded.
FUEL PUMP SHUT-DOWN
New to the MRS III system is the link via the K-Bus/CAN Bus to the Engine Control Module
for deactivation of the fuel pump. The MRS III will signal the DME over the K-Bus through
the instrument cluster and CAN Bus to shut off the fuel pump in the event that any crash
threshold is exceeded.