1999 BMW 540i Oul

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Airbag System (SRS)~
Warnings
When servicing airbag equipped cars, the following precau-
tions must be
observed to prevent personal injury.
WARNING-
. If the airbag indicator light is on, there is a risk that the air-
bags will not be triggered in case of an accident Be sure
to have the system inspected and repaired immediately
Airbag(s) are inflated by an explosive device. Handled
improperly or witliout adequate safeguards, the system
can be very dangerous. Special precautions must be
observed prior to any work at or near the airbags.
0 The airbag is a vehicle safety system. Serious injury
may result if system service is attempted by persons
unfamiliar with the BMW
MRS and its approved service
procedures. BMW advises that all inspection and ser-
vice be performed by an authorized BMW dealer.
Always disconnect the battery and cover the negative
(-) battery terminal with an insulator before starting di-
agnostic, troubleshooting or service
work not associat-
ed
with the airbags, and before doing any welding on
the car.
0 After disconnecting the battery, wait 5 seconds before
beginning work on
airbag components.
* If an airbag has been activated due to an accident,
BMW specifies that
airbag components be replaced.
For more information on post-collision
airbag service,
see an authorized BMW dealer.
Do not fire an
airbag unit prior to disposal. It must be
fired by a special disposal company or shipped back to
BMW in the packaging of the new components.
When removing a fired
airbag unit, avoid contact with
the
skin; weargloves. In case ofskin contact, wash with
water.
Do not allow
airbag system components to come in
contact with cleaning solutions or grease. Never sub-
ject
airbag components to temperatures above 167°F
(75°C). When reconnecting the battery, no person
should be inside the vehicle.
Always place an
airbag unit that has been removed
from its
packaging with the paddedside facing upward.
Do not leave an
airbag unit unattended.
0 If the airbag unit or airbag control module has been
dropped from a height of
'/? meter (I//: ft.) or more, the
airbag unit should not be installed.

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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-

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721 -1 0
/Airbag System (SRS)
4 Pry up cover from top of passenger side airbag on dash-
board.
4 Remove airbag mounting bolts (arrows)
- Lift airbag and disconnect electrical harness connector. Re-
move
airbag.
WARNING-
Store the removed airbag unit with the soft pad facing up. If
stored facing down, accidental deployment could propel it vi-
olentlv into the
ail: causino inium
- Installation is reverse of removal. Make sure wiring harness
is not pinched when installing
airbag unit in dashboard.
Tightening torques
-
Passenger alr bag to 10 NM (88 in-lb)
dashboard (Me)
Door mounted side-impact airbag,
removing and installing
- Disconnect negatlve (-) cable from battery and cover nega-
tive terminal with insulating material.
CAUTION-
Prior to disconnecting the battea read the battery discon-
nection cautions given
in 001 General Warnings and Cau-
tions.
- Remove inside door panel as described in 41 1 Doors

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- -
On-Board Diagnostics
Professional diagnostic scan tools available atthe time of this
printing include the BMW factory tools
(DISplus, GTI,
MoDiC) and a small number of aftermarket BMW-specific
tools. See
020 Maintenance.
In addition to the professional line of scan tools, inexpensive
generic OBD
II scan tool software programs and handheld
units are readily available. Though limited, they are
nonetheless powerful diagnostic tools. These tools read live
data streams and freeze frame data as well as a host of other
valuable diagnostic data.
Diagnostic monitors
Diagnostic monitors run tests and checks on specific
emission control systems, components, and functions.
A complete drive cycle is requiredforthe tests to bevalid. See
Drive cycle in this repair group. The diagnostic monitor
signals the
ECM of the loss or impairment of the signal or
component and determines if a signal or sensor is faulty
based on
3 conditions:
* Signal or component shorted to ground
Signal or component shorted to
B+
Signal or component missing (open circuit)
The OBD
II system monitors all emission control systems that
are installed. Emission control systems vary by vehicle model
and year. For example, a vehicle may not be equipped with
secondary air injection, so no secondary air readiness code
would be present.
OBD
II software monitors the following:
Oxygen sensors
Catalysts
Engine misfire
- Fuel tank evaporative control system
Secondary air injection Fuel system
Oxygen sensor monitoring. When driving conditions allow,
response rate and switching time of each oxygen sensor is
monitored. The oxygen sensor heater function is also
monitored. The OBD
II system differentiates between
precataylst and post-catalyst oxygen sensors and reads each
one individually. In order
forthe oxygen sensor to be
effectively monitored, the system must be in closed loop
operation.

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On-Board Diagnostics
Catalyst monitoring. Thisstrategy monitors the outputofthe
precatalyst and post-catalyst oxygen sensors, comparing the
oxygen content going into the catalytic converter to the
oxygen leaving the converter.
The diagnostic executive
lknows that most of the oxygen
should be used up during the oxidation phase. If it detects
higherthan programmed values, afault is set and the MIL
illuminates.
Misfire detection. This strategy monitors crankshaft speed
fluctuations and determines if an enoine misfire occurs bv
monitoring variations in speed between each crankshaft
sensortrigger point. This strategy is so finely tuned that it can
determine the severity of the misfire.
The system determines
if a misfire is occurring, as well as
other pertinent misfire
information such as:
Specific
cylinder(s)
Severity of the misfire event
Emissions relevant or catalyst damaging
Misfire detection is an on-going monitoring process that is
only disabled under certain limited conditions.
Secondary air injection monitoring. Secondary air
injection is used to reduce HC and CO emissions during
engine warm up. Immediately following a cold engine start
(-1 0" to 40°C), fresh air (and therefore oxygen) is pumped
directly into the exhaust
manifold. By injecting additional
oxygen into the exhaust manifold, catalyst warm-up time is
reduced.
Secondary air system components are:
Electric air injection pump
* Electric pump relay
* Non-return valve
Vacuum
I vent valve
- Stainless steel air injection pipes
Vacuum reservoir
The secondary air system is monitored via the use
of the pre-
catalyst oxygen sensors. Once the air pump is active and air
is injected into the system, the signal at the oxygen sensor
reflects a lean condition. If the oxygen sensor signal does not
change, a fault is set and the faulty
bank(s) identified. If after
completing the next cold startafault is again present, the MIL
illuminates.