1999 BMW 540i steering

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E39 brake system
BMW E39 models are equipped with vacuum power-assisted
four-wheel disc brakes with an integral
Antilock Brake System
(ABS). Single-piston calipers act on vented front and rear ro-
tors. A brake pad wear sensor for each axle indicates when
brake pads need replacement. The dual drum-type parking
brake system is integrated with the rear brake rotors.
Electronic braking and stability control
E39 models were introduced with Automatic Stability Control,
a computer controlled traction control system that uses the
AB5 system in conjunction with engine management controls
to control wheel spin during take-off and maintain vehicle sta-
bility while braking.
Added in the
1998 model year was Dynamic Stability Control
(DSC). This system implements wheel speed modulation
throughout all stages of driving. For example, DSC is able to
reduce understeer by applying differing amounts of braking
force to each wheel, or it can override the engine manage-
ment system during hard cornering.
A summary of distinguishing characteristics of the various
systems is shown in the table
E39 electronic braking and
stability control systems.
For ABS, ASC and DSC system and component descriptions,
see
300 Suspension, Steering and Brakes-General.
WARNING-
A car with electronic stability control is still subject to normal
physical laws. Avoid excessive speeds for the road conditions
encountered.
E39 electronic braking and stability control systems
Year (model)
manuf. up to 911998
(528i, 540i)
manuf. from 911999
(540i optional)*
From
911 999
(ail models) System
Automatic Stability Control (ASC) Identifiers
Electronic control module next to glove compartment
Hydraulic unit in right rear of engine compartment
No precharge pump
Dynamic Stability Control
(Bosch DSC
Ill v. 5.3)
Dynamic
Stabil~ty Control
(Bosch DSC
Ill v. 5.7) Electronic
control module next to glove compartment
Hydraulic unit in right rear of engine compartment
Precharge pump in left front of engine compartment, below steering
fluid reservoir
Separate rotational rate (yaw) and lateral acceleration sensors
Control
modulelhydraulic unit in right rear of engine compartment
No precharge pump
Combined rotational rate (yaw) and lateral acceleration sensors

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Brakes
Troubleshooting
Brake performance is mainly affected by three things:
Q Level and condition of brake fluid
Ability of bralte system to create and maintain pressure
Condition of friction components
Air in bralte fluid will
make the brake pedal feel spongy during
braking
orwill increase the bralte pedal force required to stop.
Fluid contaminated by moisture or dirt can corrode the sys-
tem. lnspect the brake fluid inside the reservoir. If it is dirty or
murky, or is more then two years old, replace fluid.
To
check the function of the master cylinder hold the bralte
pedal down hard with the engine running. If the pedal slowly
falls to the floor, either the master cylinder is leaking internal-
ly, or fluid is leaking externally.
lnspect the rotors for glazing, discoloration and scoring.
Steering wheel vibration while braking at speed is often
caused by warped rotors, but can also be caused by worn
suspension components.
When troubleshooting, keep in mind that tire inflation, wear
and temperature can all have an affect on braking. See
300
Suspension, Steering and Brakes-General for additional
suspension and brake system troubleshooting.
The table Brake system troubleshooting lists symptoms of
brake problems, probable causes, and suggested corrective
actions. Unless noted otherwise, relevant repairs are de-
scribed later in this repair group.

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1 Brakes
Max. machine limit per
friction ring side 0.8 mm (0.03
in) I
Brake rotor reconditioning specifications
Model
Replace
braite rotors in pairs
Bralre rotor sizes
Clean rotor with brake cleaner before installing.
Front
Model
6-cylinder
models (5251,
5281, 530i)
V-8 models (540i)
* When installing new rear brake rotors, adjust pariting brake
as described later, in Parking brake, adjusting. Rear
Vented rotor wear limit (min. thickness)
Tightening torques
Braite rotor to hub 16 Nm (12 ft-lb)
6-cylinder models
(525i, 5281, 530i)
- V-8 models (540i)
Front
296 mm (1 1.65 in)
324 mm (12.76 in)
Front bralte pad
carrler to steering ltnucitle 110 Nm (81 ft-lb)
Rear
298 mm (1 1.73 in)
Rear
brake pad carrier to wheel bearing carrier 65 Nm (48 ft-lb)
20.4
mm (0.80 in)
28.4 mm (1.12 in)
Road wheel to hub
120ilONm
(89 -t 7 it-lb)
18.4 mm (0.72 in)
The brake master cylinder is mounted to the front of the vacu-
um booster on the driverside bullthead.
-
CAUTION-
All E39 vehicles soldin the USA are equipped with Antilock
Braling System (ABS) and either Automatic Stability Control
(ASC) or Dynamic Stability Control (DSC).
In order for the
braling and stability controls to work properk if the brake
master cylinder is replaced, make sure that the brake system
is bled
by an authorized BMW dealer or other qualified repair
facility
using the BMW Service Tester. See Brake Bleeding
earlier
in this group.

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1 Brakes
ABS COMPONENT REPLACEMENT
CA UTIOW-
If the tires on the car are of different makes, the ABS/trac-
tion controlsystem may overreact. Only fit tires of the same
make and treadpattern.
In adverse conditions, such as trying to rock the car out
of deep snow or other soft surface, or when snow
chains are fitted, it is advisable to switch off traction
control and allow
tlie car driveline to operate conven-
tionally.
All E39 vehicles are equipped with
Antilock Braking System
(ABS). Early production models featured ABS with Automatic
Stability Control (ABS
I ASC). Later models came equipped
with ABS and Dynamic Stability Control (ABS
/ DSC). This
manual will refer to these systems as ABS. ASC or DSC will
be specified when necessary.
For ABS system and component descriptions, see
300 Sus-
pension, Steering and Brakes-General.
Wheel speed sensor, replacing
- Raise applicable end of car.
Make sure that the car is firmly supported on
jack stands de-
signed for the purpose. Place
jack stands beneath structural
chassis points. Do not place jack stands under suspension
< Front sensor: Unscrew mounting bolts (arrows) at steering
knuckle.
4 Rear sensor: Unscrew mounting bolt (arrows) in rear wheel
bearing carrier.
NOTE-
ABS wheelspeed sensor application may vary depending on
traction control system installed.

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4 Disconnect and remove speed sensor electrical harness (ar-
row) from retaining mounts. (Lefl front wheel shown).
- During installation, apply thin coat of StaburagsBNBU 12/K
or equivalent grease to speed sensor and housing.
- Installation is reverse of removal.
Tightening torque
ABS wheel speed sensor to steering knuckle or 8 Nm (6 It-lb)
rear wheel bearing carrier
ABS impulse wheel
The front and rear impulse wheels are integral with the inner
wheel bearing seal and not available as separate part. See
310 Front Suspension or 330 Rear Suspension for wheel
bearing replacement procedures.
DSC lateral acceleration or rotational rate
(yaw) sensor, replacing
DSC system on 1998 cars (Bosch DSC Ill v. 5.3): Lateral ac-
celeration sensor and rotational rate (yaw) sensor are sepa-
rate units, both mounted underneath or in front of driver's
seat.
DSC system on 1999 and later cars (Bosch DSC
Ill v. 5.7):
Lateral acceleration sensor and rotational rate (yaw) sensor
are combined into one unit, located under driver's seat.
- Remove driver's seat. See 520 Seats.
- Lateral acceleration sensor (1 998 models): Remove lower
lefl door pillar trim (driver's
kick panel) to access sensor. Pull
up carpet as necessary to reach sensor harness connector
or fasteners.
4 Rotational rate (yaw) sensor (1998 models): Remove plastic
trim at door sill to access sensor (arrow). Pull up carpet and
move insulation forward as necessary to reach sensor har-
ness connector or fasteners.
- Combined lateral acceleration / rotational rate (yaw) sensor
(1 999 and later models): Remove plastic trim at door sill to
access sensor. Pull up carpet and move insulation forward as
necessary to reach sensor harness connector or fasteners.
- Disconnect electrical harness connector at sensor.
- Combined sensor (1 999 and later models): Remove sensor
bracket mounting screws.

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340-28
Brakes
- Remove sensor mounting screws. Lift sensor away from
bracket.
- Installation is reverse of removal.
CAUTION-
Be sure to tighten the DSC acceleration sensor(s) and
mounting bracket, if applicable, to specified torques. The
sensor
is vibration sensitive and subject to cause DSC
malfunctions if installed improperly.
a After replacing the sensor, perform sensor adjustment
using either DIS or
MoDiC under Service Functions
menu.
Tightening
torques
Lateral acceleration I rotational rate sensor 8 Nm (6 R-ib)
to bracket
Sensor bracket to body
8 Nm (6 ft-lb)
DSC steering angle sensor, removing and
installing
4 Remove lower dash panel mounting fasteners (A) and (5).
- Remove steering column lower trim panel. See 320 Steering
and Wheel Alignment.
Remove steering shaft clamping bolt (arrow).
Disconnect sensor wiring harness connector.

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Remove snap ring from steering shaft.
- Slide steering angle sensor off steering shaft
< Installation is reverse of removal, noting the following.
Take care to line up loclting pin
(arrow) with mount hole in
sensor.
Perform steering angle offset test using BMW scan tools
DISplus, GT1, or MoDiC. Once calibrated, the sensor
sends a confirmation ID code to the DSC control module
to indicate proper calibration.
DSC precharge pump, removing and
installing
(1 998 models)
1998 V-8 cars with Bosch DSC Ill v. 5.3 are equipped with a
DSC precharge pump mounted in the engine compartment.
There is no separate precharge pump in the Bosch DSC
Ill v.
5.7 system (1999 models and later).
WARNING-
E39 cars require special BMWservice equipment to properly
bleed the brakes. Removal of hydraulic components is not
recommended unless this equipment is available. For safety
reasons, the
brake system on cars with ABS must be bled us-
ing the procedures described in this repair group.
- Using a clean syringe, empty brake fluid reservoir.
CAUTIOI\C
Brake fluid is highly corrosive and dangerous to the environ-
ment. Disoose of it
orooerlv.
Working at precharge pump, disconnect hydraulic lines (A)
and electrical harness connector (6). Clean up dripping fluid.
hydraulic unit. Label all
con-

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340-31
Brakes
ABS 1 traction electronic control module
(1 997 -1 998 models)
4 The traction control electronic control module in 1997- 1998
models is located to the left of the glove compartment.
NOTE-
In both ASC and early DSC systems this location is used for
the electronic control unit.
- Before removing the traction control electronic module, read
any fault codes in memory.
ABS I DSC control module
(1 999 - 2002 models)
The DSC electronic control unit in 1999 and later models
(from 911998) is bolted to the DSC hydraulic unit in the right
rear of the engine compartment.
- Before removing the traction control electronic module, read
any fault codes in memory.
- Install electronic control unit using new screws.
Tightening torque
DSC electronic control unit to 2.9 Nrn (26 in-lb)
hydraulic
unit (use new screws)
- Code newly installed module using either DIS or MoDiC.
- Adjust steering angle sensor using menu item Service func-
tion in
DIS or MoDiC.
ABS I traction control hydraulic unit,
removing and installing
WARNING -
E39 cars require special BMWsewice equipment to properly
bleed the brakes. Removal of the hydraulic unit is not recom-
mended unless this equipment is available. For safety rea-
sons, the
brake system on cars with ABS must be bled using
the procedures described in this repair group.
NOTE-
Before starting this procedure, read control module mem-
ory and print
out diagnostic record.
DSC system: Adjust steering angle sensor using
either
DISplus, GTI, or MoDiC. After completing work, function
test control module.