2000 BMW 7 SERIES MRSIII Multiple Restraint System Manual

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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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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MRS III I-P-O

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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.

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DIAGNOSIS
Diagnosis and troubleshooting of the MRS III system is fault driven and can be accessed
using the DIS Tester or MoDiC. The control module performs a self test of the system every
time the ignition is switched on ( this includes the satellite sensors and seat occupancy sen-
sor). Any faults with the system will cause the warning lamp in the instrument cluster to
remain illuminated after the engine is started.
Installation of a new or replacement control module requires ZCS coding also using the DIS
or MoDiC.
When servicing or replacing any MRS III components, always follow precautionary mea-
sures outlined in the repair manual of TIS. this includes disconnecting the battery prior to
any repair or maintenance work being performed.
All airbag components are part number specific by model and require verification in the
EPC to ensure the correct component is being installed.