Part 1

Dynamic Stability Control

NOTE: Structure of this document.

The most important diagnosis instructions are described at the start of this document. These are followed by the functional description.

Diagnosis instructions

Remedying faults and/or deleting the fault memory
If problems occur on deleting the fault code memory following a repair, use the following procedure:
1. Delete fault with ignition off.
2. Ignition on, delete stored faults.
3. Ignition off, wait 5 - 10 seconds and switch ignition back on.
4. Clear fault memory again.

IMPORTANT: In some cases, indicator and warning lights for certain faults only go out after a short test drive.

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 the cruise-control system must be coded using Progman.
With regard to the DSC function, the DSC control unit codes itself. In this operation, the vehicle identification number is also stored. It is thus not necessary to synchronize the steering-angle sensor with DSC 8 or DSC 8Plus.
For every startup (ignition on), the DSC compares the stored vehicle identification number with the current vehicle identification number. DSC codes itself according to the type of vehicle if the vehicle identification numbers do not match. This opportunity is used to reset the learned adjustment values of the sensors to the base setting (exception: longitudinal acceleration sensor). Perform the following operations:
1. Encoding DSC
2. Brake bleeding procedure for DSC unit
3. Brake line mix-up test:
4. Initialize Run Flat Indicator (see Owner's Handbook)

Replacement of DSC sensor
After replacement of the DSC sensor, the service function "Adjustment DSC sensor" must be run. The longitudinal acceleration sensor is adjusted in the DSC sensor.

Replacement of steering angle sensor
The steering angle sensor forms a unit with the steering column switch cluster. The steering angle sensor cannot be replaced on its own. The service function "Adjustment steering angle sensor" or in the case of vehicles with active steering the service function "Commissioning/aligning active steering" must be run after the following work:
- Replacement of steering column switch cluster (SZL)
- only E60, E61, E63, E64: programming steering column switch cluster (SZL in the E70 and E71 not programmable)
- only E70, E71: replace DSC control unit (because the DSC synchronizes the SZL)
- Adjusting procedure on the steering geometry
- Work on the steering and/or front axle

Introduction

Dynamic Stability Control
The X5 is equipped with Dynamic Stability Control (DSC) as standard equipment. DSC is a development of the DSC 8Plus. To make a distinction, this suspension control system is called "DSC Premium". System supplier for the DSC is Bosch.
E60, E61, E63, E64 receive DSC Premium starting in 03/2007.
The control functions of the DSC have been optimized. The improvement was achieved by installing a return pump with 6 pistons as well as more powerful electronics. Compared to the previous model (E53) the E70 and E71 incorporate expanded functionality:
- Brake standby by pre-emptive application of brake pads in case of need (creation of low anticipatory brake pressure)
- "Dry braking" of the brake discs on wet roads with wipers switched on
- Detection of fading and increase in the brake pressure in the event of fading
- Drive-off assistant
- Cruise control with braking function (SA544)
- Parking brake (electromechanical and hydraulic parking brake)

Further road safety results from the combination with other systems:
- Yaw moment compensation with active steering (SA217)

DSC is a driving dynamics system that maintains driving stability. DSC optimizes:
- driving stability on driving off, accelerating, cornering as well as braking
- traction

The DSC also detects unstable driving conditions such as understeer or oversteer. DSC helps to maintain the vehicle on a safe course within the physical boundaries.
To do so, the DSC must be aware of the following dynamic measurement variables:
- The yaw rate as a measure for the rotary motion of the vehicle around the vertical axis
- Lateral acceleration
- Wheel speeds

In addition, the driver's choice is detected from the steering angle and the brake pressure the driver applies to the pedal. Furthermore, wheel speed sensors deliver information on the speed of the individual wheels. The available measured values are used to determine the actual condition in which the vehicle is moving at the moment. The actual condition is compared with nominal values calculated in the DSC control unit. If the current actual values deviate from the desired state, DSC becomes active and actively intervenes in the brake system or in the engine control, as the case may be.

Brief component description
The following components for dynamic stability control are described:

DSC unit
The DSC unit consists of the DSC control unit and a hydraulic unit. The DSC control unit activates the hydraulic unit via valve coils.







The DSC unit contains a brake pressure sensor. This brake pressure sensor registers the braking pressure applied by the brake pedal and the brake booster. The brake pressure sensor has a measuring range from 0 to 250 bar. Its zero point is only synchronized while the vehicle is being driven.
The new concept of the DSC unit enables more exact control. 2 x 3 pump elements with 1 6.5 mm work in the pump motor. This concept results in significantly improved pressure dynamics. It means that the brake pedal pulses to a lesser degree during ABS control. It also leads to higher control quality with Hill Descent Control (HDC).







The power distribution box at the junction box electronics (JBE) supplies the DSC unit with voltage. Once terminal 30 for the return-flow pump, once terminal 30 for the solenoid valves. The DSC control unit receives terminal 30g.

4 wheel speed sensors
The active wheel-speed sensors determine the circumferential wheel speed of the individual wheels. In addition, the wheel-speed sensors detect the direction of rotation (forwards or backwards). When a wheel is at a standstill, the wheel-speed sensor transmits an impulse every 0.75 seconds. The current impulse indicates the availability of the wheel-speed sensor.
The following advantages result from active wheel-speed sensors:
- rapid and reliable detection of the direction of travel
- improved activation of the gearbox control
- Improved actuation of navigation system







On the front and rear axles, there is a circle of magnets (increment wheel) around the wheel bearing. The north and south poles of the increment wheel alternate. A north pole with a south pole corresponds to 1 increment (comparable to one tooth and one gap on a reluctor ring). The wheel-speed sensor consists of 3 Hall sensors and an electronic evaluation unit.
The active wheel-speed sensors change their electrical resistance under the influence of a magnetic field. Each increment causes 2 impulses in the wheel-speed sensor (96 impulses / rotation of wheel). For data transfer to the control unit, additional data is appended to the edge of the impulse. Functionally, this integrated data processing goes beyond pure engine speed detection. The following additional information is possible, e.g.:
- Wheel's direction of rotation
- Air gap
- Vehicle at a standstill

DSC sensor
The DSC sensor measures:
- Rotation of the vehicle around the vertical axis (yaw rate)
- Lateral acceleration of the vehicle
- Longitudinal acceleration of vehicle







The sensor element consists of 2 piezoelectric acceleration sensors. A spring-mounted weight is hung in the measuring cell of the acceleration sensor. During accelerated motion the 2 masses suspended on their compliance elements are also accelerated. The force necessary for this creates a mechanical voltage in the piezoelectrical material. The shift in electrical charge this creates is picked up with electrodes made of metal and processed as an electrical signal. The yaw rate is derived from the difference between the two acceleration signals.The DSC sensor thus delivers a yaw rate and an acceleration signal.
The longitudinal acceleration sensor is required for the drive-off assistant.
The DSC sensor is connected via the chassis CAN (F-CAN) with the DSC control unit.
The DSC control unit supplies the DSC sensor with voltage.

Steering angle sensor
The steering angle sensor is installed in the steering column switch cluster (SZL). The steering angle sensor measures the steering wheel angle optically and without contact. The steering angle sensor is fitted on the printed circuit board with the evaluation electronics. The steering angle sensor consists of the following components: encoded disc and optical sensor.
The encoded disc is connected to the steering wheel via the coil spring cassette. When the steering wheel is moved, the encoded disc moves within the optical sensor. There are various line patterns for evaluation on the encoded disc.







The SZL is connected via the chassis CAN (F-CAN) with the DSC control unit.

DTC button and HDC button
The DTC button is used to change the operating mode of the chassis control system. The DTC button bears the lettering "DTC". The DTC button can be used to select 3 switching modes:
- DTC button not pressed after terminal change: DSC in operation (standard)
- Press DTC button briefly: DTC in operation (notification "DTC" appears in the instrument cluster above indicator lamp)
- Press DTC button for longer period: DSC and ASC switched off, ABS and ABD-X still active (indicator lamp in instrument cluster lights up continuously)

E70, E71: The DTC button is located in the centre console control panel (no control unit). The centre console switching centre is connected to the integrated heater / automatic climate control (IHKA). The IHKA sends the signal on the K-CAN.
E60, E61, E62, E63 from 03/2007: The DTC button is in the switch block on the left, next to the ashtray. The switch block is connected to the centre console switch centre (SZM). The SZM control unit is installed in the carrier behind the glove compartment.







E70:The HDC button is also in the centre console control panel.
E60 and E61: Those buttons on the steering column available for programming as desired can be assigned to control the Hill Descent Control (HDC). The HDC can also be activated via iDrive.
The DSC receives additional input signals from the following components:

Brake fluid level switch
A low brake fluid level is picked up (in the expansion tank via a reed contact) and notified to the DSC control unit. With a low brake fluid level, DSC is disabled. Otherwise, there is a danger that air will be drawn into the brake system.

Brake light switch
Together with the signal from the brake pressure sensor, braking operations are detected. Two switches (2-stage) are installed in the brakelamp switch. A signal is then made available to the DSC across a line. The engine control unit receives both signals. The engine control unit sends the signal on the PT-CAN. The DSC control unit uses both signals to detect whether the brake pedal has been pressed.







The Car Access System (CAS) supplies the brake-light switch with terminal R.

2 brake pad wear sensors
The brake pad wear sensors (front left and rear right in the inner brake pads) provide additional information on the thickness of the brake pad. This additional information (2 data points) is compared to the value calculated by the DSC.







A critical brake pad thickness is indicated in the instrument panel by a Next Service indicator (Condition Based Service CBS) as well as the red general brake warning light.
The following additional control units are involved in the dynamic stability control:

KOMBI: Instrument panel
In the event of failure of or a fault in the DSC, a Check Control symbol appears in the liquid crystal display. The Check Control symbols all have a certain meaning.
If there is a Check Control message, additional supplementary instructions can be displayed on the central information display (CID).

CAS: Car Access System
The CAS receives a processed speed signal from the DSC. The CAS recognizes from the signal whether the vehicle is stationary or moving.

JBE: Junction Box Electronics
The power distribution box at the JBE supplies the DSC unit with voltage. Terminal 30 for the return pump and the solenoid valves. Terminal 30g for the DSC control unit.