1997 BMW 540i 721 airbag

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l Seats
Seat repair and component replacement is possible once the
seat has been removed from the vehicle.
Before servicing front seats read safety regulations on han-
dling
airbag modules and pyrotechnic seatbelt tensioners.
See
720 Seat belts and 721 Airbag system (SRS).
WARNING-
. The front seats are equipped with pyrotechnic seat belt
tensioners. These tensioners are powerful devices and
should be handled with exfreme care. Incorrect handling
can trigger off the tensioner and cause injury.
BMW recommends that all repair or replacement
worlc
on pyrotechnic devices must be carried out by a quali-
fied
BMW technician.
Be sure to disconnect the battery and wait
5 seconds
before attempting to work on pyrotechnic devices.
During body straightening and welding with an electric
arc welder, always disconnect the battery and the con-
nection to the pyrotechnic gas generators.
Seat switch and memory module, removing
and installing
- Remove front seat. See Front seats, removing and install-
ing.
- Carefully pull seat adjusting ltnobs straight out to remove.
Remove screw fastener
(A) and trim clips (B), turn side panel
downward to remove.
Disconnect electrical harness connector
(arrow).

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I Seat Belts
This section covers repairs to the following seat belts sys-
tems. See the table below.
IMultIple Restraint Systems I
Years
311 996 - 811 997
Multiple Restraint System electronics integrate seat belt op-
erations and
airbag deployment. Airbag repair information is
covered
in 721 Airbag System (SRS).
Troubleshooting
The seat belt reel should lock when driving quicltly through
curves,
during severe braking or in case of a collision. The au-
tomatic reel does not require any servicing and should never
be opened.
- In case of an accident, follow the seat belt troubleshooting
procedures presented
in the table below.
Troubleshooting procedures
Belt creased, unraveled, pinched, cut or
melted. Belt buckle or belt loclt plastic casing Repairs
Replace complete automatic
seat belt.
Also
checlt and replace, if necessary, seat
Problem
Damage to seat
belt.
worn, damaged or missing.
Seat belt bucltle is not ejected with spring
pressure when red button on seat belt loclt is
>--- I I
Automatic belt soueaks when fastened or I~xcessive friction in belt guides. I Replace reel assembly.
Probable
cause
Accident in which bumper impact absorbers
were permanently deformed.
Seat belts aged or worn.
pressed.
Seat belt automatic reel does not lock when
pulled out suddenly.
Seat belt automatic reel jams when pulled
out.
Seat belt does not retract automatically
(see note below).
Automatic reel loose. Return sorino broken inside reel. belt mounting on car body and
seat belt
mounting on seat runner.
Replace complete automatic seat belt.
Seat belt
loclt mechanism worn or
damaged.
Tighten reel mounting bolt Replace reel assembly.
Replace seat belt lock.
Automatic reel defective.
Automatic reel loose. Return spring
broken inside reel.
Automatic reel loose.
Return spring brolten inside reel. Replace reel
assembly.
Tighten reel mounting
bolt.
Replace reel assembly.
Tighten reel mounting bolt. Replace reel assembly.
~ ~-~~ , - I'
Replace complete automatic seat belt.
Also check retaining bracket of belt
Seat belt
pyrotechnic tensioner triggered. Accident triggered pyrotechnic deployment.

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721 Airbag System (SRS)
........................... General ............................ 721-2 Airbags 721-8
..... E39Airbags ......................... 721-3 Driver airbag. removing and installing 721-8
Two-stage airbag (MRS 111) ............ .72 1.4 Passenger airbag. removing and installing . 721-9
Airbag indicator light .................. .72 1.4 Door mounted side-impact airbag.
............... Warninas .......................... .72 1.5 removina and installina 721-10 .
..... Head protection airbag components 721
-1 1 Airbag Electronics ................. '721-6 Head protection airbag (HpS) .......... 721-12 MRS ............................... 721-6
MRS
airbag system diagram ........... .72 1.6
MRS control module. replacing ......... .72 1.7
Side-impact crash sensor.
removing and installing
................ .72 1.7

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721 -2
l~irba~ System (SRS)
This repair group covers airbag components and replace-
ment.
Airbag system repairand fault diagnosis is not covered.
Diagnostics, component testing, and
airbag system repair
should be carried out by trained BMW service technicians.
Individual
airbag system components can only be tested elec-
tronically when installed in the car. BMW service testers
DIS
or MoDiC or equivalent must be used for diagnostic work.
WARNING-
Special test equipment is required to retrieve airbag fault
codes, diagnose system faults, and
reseffturn off the air-
bag indicator light. The indicator light will remain on until
any problem has been corrected and the fault memory has
been cleared.
Airbags are part of the BMW Multiple Restraint System
(MRS). Three versions of MRS are available in E39 models.
Multiple Restraint Systems
MRS and MRS II include the following restraint components:
311 996-811 997
911
997-311 999
311 999-2002
Driver and passenger front
airbags (MRSIMRS II)
MRS
MRS
II
MRS Ill
Passenger front two-stage airbag (cars manufactured
from
911998).
The seat occupancy sensor (SBE) is used for detection of
a passenger in the right front seat. MRS uses the SBE in-
put to determine seat belt tensioner
and/or front airbag de-
ployment thresholds.
Side impact
airbag for driver and front passenger
(MRSIMRS II)
Leftlright side impact crash sensors (MRSIMRS 11)
Side impact airbag for rear passenger (MRS II) (optional)
Head Protection System (HPS) for driver and front passen-
ger (MRS
II)
Battery Safety Terminal - BST (MRS II)
Hall Sensor seat belt switches (MRS II)
Front pyrotechnic seat belt tensioners
Fuel pump cut off message

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721 -3
Airbag System (SRS)
MRS Ill adds the following features:
MRS
Ill employs "smart" technology. Smart technology re-
fers to the control module's programming for the deploy-
ment of the airbags, in stages depending on the severity of
the impact.
Two-stage a~rbag for ooln drver and passenger Alloivs for
a softer
c~snioning elfecl when the airbags are lr ggered at
lighter impact,
MRS
Ill satellite sensors use 2 wire connectors
Rear side
airbags arrive de-activated from the factory and
can only be activated upon written request from the cus-
tomer.
Rear seat head protection is available when ordered with
optional rear seat side airbags.
E39 Airbags
Driver airbag
Passenger airbag
Head Protection System (HPS)
Inflatable Tubular Structure
(ITS) (MRS
II and MRS Ill)
Front side impact airbag
Rear door side impact airbag
(optional) (MRS I1 and MRS Ill)

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721-6
I Airbag System (SRS)
MRS
The MRS control module contains the electronic crash sensor
for frontal impact. Sensors mounted on the driver and
pas-
sengerfloor are used for side impacts. The MRS control mod-
ule
is located between the front seat under the center
console.
MRS airbag system
diagram
1. Driver's side airbag
2. Passenger's side airbag
3. Right side impact sensor
4. Seat occupancy sensor pad
5. Right side impact airbag
6. SBE control module (analog to
digital converter)
7. Passenger pyrotechnic seat belt
tensioner and seat belt
mi-
croswitch (Hall sensor MRS Ill)
8. MRS control module
9. Driver pyrotechnic seat belt ten-
sioner and seat belt microswitch
(Hall sensor MRS
Ill)
10. Left side impact airbag
11. Left side impact sensor

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721 -8
(Airbag System (SRS)
4 Remove electrical harness connector from crash sensor (A).
Remove sensor retaining screws (6) and remove sensor.
Note direction of sensor before removing.
- Installation is reverse of removal,
NOTE -
Arrow on sensor must point to door sill.
Driver airbag, removing and installing
- Disconnect negative (-) cable from battery and cover nega-
tive terminal with insulating material.
WARNING-
After disconnecting the batter)! wait 5 seconds before begin-
ning work on
airbag components.
CAUTION-
Prior to disconnecting the batter)! read the battery discon-
nection cautionsgiven
in001 General Warnings and Cau-
tions.
4 Multifunction (MFL) steering wheel:
. Working behind steering wheel, completely loosen Torx
screws
(T30) while holding airbag in place.
Support
airbag unit to prevent it from falling out.

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721 -9
Airbaq System ~SRS)~
4 Sport steering wheel:
Insert screwdriver through opening in rear of steering
wheel and push against spring tension to release
airbag
unit lock.
Repeat procedure on other side of steering wheel.
Lift off
airbag unit and detach electrical harness connec-
tors.
WARNING-
Store the removedairbag unit with the horn pad facing up.
If stored facing down, accidental deployment could propel
it violently into the air, causing injury.
Once an
airbag is removed, the car must not be driven.
Do not connect the battery with the
airbag disconnect-
ed. A fault code will be stored, setting off the
airbag in-
dicator light Special tools are needed to reset the fault
memory
Once the
airbag unit is installed and all other service
procedures have been completed, start the engine and
check that the
airbag indicator light goes out. If the in-
dicator light stays on, the
airbag system will not func-
tion as designed. Have the system diagnosed and
repaired by an authorized
BMW dealer.
- Installation is reverse of removal.
MFL steering wheel: Torque airbag using specification list-
ed below.
- Sport steering wheel: Press airbag unit mounting pins into
spring
loclts in steering wheel until they snap in firmly.
CAUTION--
Do notpinch airbag harness in center of steering wheel when
installino
airbaa.
Tightening torque
Airbao to steerino wheel IMFL) 8 Nm (71 in-lb)
Passenger airbag, removing and installing
- Disconnect negative (-) cable from battery and cover nega-
tive terminal with insulating material.
--
WARNING -
After disconnecting the batteg wait 5 seconds before begin-
nina work on airbaa components.
Prior to disconnecting the battery, read the battery discon-
nection cautionsgiven in001 General Warnings and
Cau-