2003 BMW X5 brake

15
DSC - NEW FEATURE
TRACTION CONTROL
The traction control feature of the DSC III on the X5 cannot be switched OFF with the DSC
switch. Pressing the button will only switch off the dynamic stability control function of the
DSC.
The traction control feature is needed at all times to provide anti-spin control especially
when driving the vehicle off road. The DSC warning lamp in the instrument cluster will still
come on when the system is switched off manually or there is a fault in the system.
Off road traction control or HDC regulation places an additional load on the brakes. To pre-
vent overheating of the brakes and rotors, the temperature of the rotors is calculated over
time from the road speed and amount of brake application. If the temperature of one or
more rotors goes above 600o
C, the traction control or HDC function for that wheel will be
cancelled temporarily. Once the temperature of the rotor goes below 500o
C, the traction
application will be re-activated.
The normal braking function (including ABS) is always active at any temperatures.
DSC - NEW FEATURE
OFF-ROAD ABS Control Module Programming
The programming for ABS regulation have changed to allow a higher threshold for ABS reg-
ulation when driving off-road in loose gravel or dirt. A locked wheel is more effective in slow-
ing or stopping the vehicle because of the wedge that is built up in front of the tire.
The programming in the DSC control module allows one or both front wheel(s) to lock up
to a speed of 12 MPH as long as the vehicle is traveling straight ahead. If the DSC control
module receives a signal from the steering angle sensor indicating a turn, ABS regulation
will activate to prevent the lock and allow the vehicle to be steered.

20
BRAKE PRESSURE SENSOR
A brake pressure sensor is installed in the hydraulic unit to determine the degree of pres-
sure build-up for Dynamic Brake Control. It is installed in the front axle brake circuit.
The sensor receives its power supply from the DSC control module and produces a linear
voltage input signal ranging from 0.5 to 4.5 volts depending on how hard the brakes are
applied.

BRAKE FLUID LEVEL WARNING SWITCH
A new fluid level switch is incorporated into the reservoir cap.
• With sufficient fluid level the reed contact is closed.
• When level drops below allowable limits, switch opens.
Since the normal position is closed, this circuit is monitored
for shorts to + and ground.
The LCM constantly monitors the input. If the ground signal is momentary,the LCM sig-
nals the Instrument cluster of the condition. The instrument cluster then informs the DSC
III control module over the CAN bus. If the signal is received just prior to the activation of
the charge pump, the charge pump activation is delayed.
If the signal is present for more then 25 seconds, the LCM issues two I BUS message for
the Instrument Cluster:
1. Post “Brake Fluid Level” in the Matrix display
2. Notify the DSC III via CAN that the Fluid level has been low for more than 25 seconds.
The DSC III control module immediately switches DSC III functions off and continuously illu-
minates the DSC indicator in the cluster.
23