Part 1
Dynamic Stability Control
Dynamic stability control (DSC)
NOTICE: Several central control units were further developed.
The functional description refers to the vehicle electrical system of the F25. Deviations with different vehicles (e.g. Front Electronic Module FEM) were documented at the appropriate location.
Diagnosis instructions
Sequence for replacement of DSC unit or DSC control unit
After replacing the DSC unit or DSC control unit The parameters for the Run Flat Indicator (RPA) as well as for the cruise control system must be coded using ISTA/P.
Perform the following operations:
1. It may be necessary to program and encode the DSC
2. Perform DSC unit brake bleeding procedure
3. Perform brake line mix-up test
4. Calibrate solenoid valves
5. Initialize Run Flat Indicator (see operating instructions)
Introduction
Dynamic Stability Control
As standard, the new BMW X3 is equipped with Dynamic Stability Control (DSC). The DSC System relies on interaction with the central driving dynamics control in the Integrated Chassis Management (ICM) and control of the transfer case (VTG). The ICM supplies the setpoint data for DSC control operation. The VTG is controlled to modulate distribution of drive torque between the front and rear axles. This allows the VTG to support the DSC control operation.
The drive dynamic control switch also influences the operating principle of the DSC. Depending on the selected stage (NORMAL, SPORT+ identical to DTC), the threshold values and characteristics of the DSC interventions also have to be adapted. In addition to the matching of the threshold values, there are still additional changes to the dynamic stability control which affect the installation location, display scopes as well as the diagnosis and repair.
Brief component description
The following components for dynamic stability control are described:
DSC unit
The DSC unit consists of:
- DSC control unit
- DSC hydraulic control unit
The DSC hydraulic control unit consists of:
- Valve block (piston pump with 2 pistons, solenoid valves, brake pressure sensor)
- Pump motor
NOTICE: The coils for the solenoid valves are integrated within the control unit. The mechanical components (valve seat, pushrods, etc.) are pressed into the valve block.
In every brake circuit, there are pairs of solenoid valves. One intake valve (de-energized open) and one discharge valve (de-energized closed). By activating these correspondingly, the brake pressure at the front wheels and rear wheels is modulated.
Changeover of the suction connections of the pump from the low pressure accumulators to the tandem brake master cylinder is performed via the electrical changeover valves.
This brake pressure sensor registers the braking pressure applied via the brake pedal and the brake servo. The brake pressure sensor has a measuring range from 0 to 250 bar. Its zero point is synchronized during driving (no adjustment diagnosis).
The DSC control unit is supplied three times with terminal 30 (pump motor, solenoid valves, control unit electronics). In the voltage supply, there are interdependencies with the automatic engine start-stop function. Observe the diagnosis wiring diagram.
Hydraulic system diagram
4 wheel speed sensors
The active wheel speed sensors are connected to the DSC control unit. The complete signal processing takes place in the active wheel speed sensors.
The wheel speed is measured at a magnetic increment wheel. The magnetic increment wheel is divided into 96 increments per rotation of the wheel. Each increment change is detected by the active wheel speed sensor and converted into a defined signal protocol of a pulse-width modulated signal.
ICM: Control unit for Integrated Chassis Management
The ICM control unit networks the suspension control systems to allow hierarchically-structured control of the vehicle's dynamic-response functions. Passive (airbag) and active safety systems have been integrated within the 2nd generation of the ICM control unit. Depending on the optional equipment selected (e. g. Vertical Dynamics Management VDM) and the national-market version (e. g. US version), there are several sensors in the ICM control unit:
- Longitudinal acceleration sensor (maximum 3 pieces)
- Lateral-acceleration sensors (maximum of 3)
- Vertical acceleration sensor
- Yaw rate sensor
- Pitch rate sensor
- Rotation-rate sensor
The sensor signals refer primarily to the co-ordinates of the sensor housing. The sensor signal values depend on the installation position. However, the driving stability control needs these variables related to the co-ordinate system of the vehicle. The ICM control unit converts the values accordingly (definition of the zero point). An adjustment of the integrated sensors is necessary after replacement of the ICM control unit. The adjustment must take place while the vehicle is on a surface that is horizontal in longitudinal direction and transverse direction. Terminal 15 must be switched on.
Rotor position sensor
New: The steering angle sensor in the steering column switch cluster (SZL) has been discontinued.
The steering wheel angle is now determined via the rotor position sensor of the electromechanical power steering (EPS). The rotor position sensor is integrated in the EPS control unit. The EPS supplies the non-linearized values for the steering angle. The ICM calculates the steering wheel angle.
There are 2 rotor position sensors (redundancy) on the printed circuit board of the control unit. Both sensors use the principle of the Hall effect (Hall sensor with magnet wheel). The magnet wheel is attached to the shaft of the servomotor.
Communication with the DSC (FlexRay) and EPS (PT-CAN) takes place via the central gateway module (ZGM).
Depending on vehicle: Communication via Front Electronic Module (FEM).
DTC button
The DTC button is located in the centre console operating facility. The DTC button is used to switch over the operating condition of the Dynamic Stability Control. The DTC button can be used to select 3 switching states:
- DTC button not pressed after terminal change: DSC in operation (standard)
- Press DTC button briefly: Switch from DSC to DTC (Dynamic Traction Control) and vice versa
- Press DTC button for longer period: DSC and ASC switched off, ABS and ABD-X still active
The centre console operating facility is connected electrically to the Integrated Chassis Management. The ICM control unit forwards the signals of the DTC button on the FlexRay to the DSC.
NOTICE: Different number of plug connections.
The centre console operating facility starting with F20 has only 1 plug connection to the Integrated Chassis Management (ICM). Observe the wiring diagrams in the diagnosis.
NOTICE: Driver experience switch depends on options fitted.
If a driver experience switch is installed, the labelling then changes {COMFORT} to {ECO PRO}. The function {ECO PRO} is described with the ICM.
Depending on the DSC mode, the indicator light in the instrument panel is switched on. The indicator light shows a skidding vehicle with the labelling "OFF" or only a skidding vehicle.
If SPORT+ is selected via the drive dynamic control switch, the system automatically switches to DTC operating condition.
The DSC receives additional input signals from the following components:
Automatic Hold button (only F25)
The "Automatic Hold" button is integrated within the parking brake button. The "Automatic Hold" button is electrically connected to the DSC control unit.
The "Automatic Hold" function supports the driver by automatically applying and then releasing the brakes, for instance, in stop-and-go traffic. At a standstill, the vehicle is automatically and continuously held hydraulically via the DSC (difference to the drive-off assistant by approximately 2 seconds). On slopes, the vehicle cannot roll back when driving off.
The EMF electromechanical parking brake must be installed for "Automatic Hold". This should not be confused with the drive-off assistant (see system functions).
A switch from hydraulic to mechanical retention is executed under the following conditions:
- The engine is turned off
- A door is opened and the driver takes off his/her seat belt.
- During a journey, the vehicle is braked to a standstill using the parking brake.
The DSC receives additional input signals from the following components:
Brake fluid level switch
The brake fluid level switch detects that the brake fluid level has dropped below the required (minimum) brake fluid level in the brake fluid expansion tank. The DSC control unit sends the signal of the bus system to the instrument panel. The instrument panel issues a Check Control message. Normal movements of the brake fluid (during braking or acceleration) in the brake fluid expansion tank will not normally lead to a Check Control message. A reed contact is installed on the side of the brake-fluid reservoir. The reed contact transmits an electrical signal if the brake fluid level falls below a specified minimum level. The reed contact is closed while the brake fluid level is above the minimum mark.
