Brakes - Service Techniques — BMW M3 E90 (2007-2013)

Scheme 136

Scheme 136: Dynamic Stability Control 8 Plus: E60, E61, E63, E64, E83, E90, E91, E92

Note. Vehicles with DSC 8Plus

This SBT describes DSC 8Plus, which is installed on the following model series

E60, E61, E63, E64 (rear and all-wheel drive)
E83
E90, E91, E92 (all-wheel drive only)

Introduction

The xDrive all-wheel drive system was introduced on the BMW 5-Series in 03/2005. From this time on, these vehicles are equipped as standard with Dynamic Stability Control (DSC) 8Plus.

DSC 8Plus is an advanced development of DSC 8.

The DSC unit (comprising DSC control unit and hydraulic unit) is even more powerful.

The newly developed switchover valves allow a more precise regulation, especially at low brake pressure. DSC 8Plus is supplied by Bosch.

The principal new features of DSC 8Plus are

Additional functions: Brake Standby through precautionary pre-tensioning of the brakes in an emergency Brake disc drying on wet roads Detection of fading and increase in brake pressure during fading Start-off assistant Soft stop when braking to standstill NOTE: New soft stop function not available on BMW 3-Series all-wheel drive or E83. For technical reasons, the soft stop function has not been incorporated on BMW 3-Series all-wheel drive or on E83 vehicles.
2 additional brake pressure sensors, only in combination with Active Cruise Control (ACC)

Brief description of components

The following components are described for the Dynamic Stability Control (DSC)

DSC unit The DSC unit consists of the components DSC control unit and hydraulic unit. The DSC control unit regulates the pressure in the brake system via the hydraulic unit (comprises valve block and pump motor).
Brake light switch The brake light switch tells the DSC when the brake pedal has been pressed.
4 wheel-speed sensors The active wheel-speed sensors register the speed of an individual wheel at their circumference. Moreover, the wheel-speed sensors also recognize the direction of rotation (forwards or backwards). When a wheel is stationary, the wheel-speed sensor emits a pulse every 0.75 seconds.
DSC sensor The DSC sensor measures: Vehicle rotation around the vertical axis (yaw rate) Lateral acceleration of vehicle Longitudinal acceleration of vehicle E60, E61, E63, E64 The DSC sensor is linked to the DSC control unit by the F-CAN (chassis CAN). The DSC sensor is secured to the floor assembly under the front-passenger seat. E83 The DSC sensor is connected to the DSC control unit via the PT-CAN (powertrain CAN). The DSC sensor is secured to the retainer plate for the parking brake lever. E90, E91, E92 The DSC sensor is linked to the DSC control unit by the F-CAN (chassis CAN). The DSC sensor is located on the seat cross member under the driver's seat.
Steering-angle sensor The steering-angle sensor registers the movements of the steering wheel. E60, E61, E63, E64 The steering-angle sensor is part of the steering column switch cluster (SZL). The steering column switch cluster is connected to the F-CAN (chassis CAN) and to the PT-CAN (powertrain CAN). E90, E91, E92 The steering-angle sensor is part of the steering column switch cluster (SZL). The steering column switch cluster is connected to the F-CAN (chassis CAN). E83 The steering-angle sensor is fitted to the steering spindle. The steering angle sensor is connected to the PT-CAN (powertrain CAN).
Internal brake pressure sensor The DSC unit incorporates a brake-pressure sensor. This brake pressure sensor registers the braking pressure applied by the brake pedal and the brake booster.
2 brake pad wear sensors The brake pad wear sensors (front left and rear right in the inner brake pads) provide additional information about the thickness of the brake pads. This additional information (2 reference points) is compared to the value calculated by the DSC. A critical brake lining thickness will be indicated in the instrument cluster by the "Next Service" indicator (Condition Based Service, CBS) and by the general brake warning lamp lighting up red.
DTC button The DTC button has the letters "DTC". The DTC button can be used to select 3 switch states: DTC button not pressed after terminal change: DSC in operation (default) DTC button briefly pressed: DTC in operation (DTC indicator light lights up in instrument cluster) DTC button pressed and held: DSC and ASC deactivated, ABS and ABD-X on all wheel drive vehicles remain active (indicator lamp in instrument cluster lights up permanently) E60, E61, E63, E64 The DTC button is in the centre console switch cluster (SZM) The signal is transmitted on the K-CAN and via a separate wire. The signal on the separate wire is decisive. E83 The DTC button is in the centre console switch cluster (SZM) The signal is transmitted via a separate wire. E90, E91, E92 The DTC button is connected to the junction box electronics (JBE). The JBE transmits a bus signal.
Brake-fluid-level switch Insufficient brake fluid is detected and a signal sent to the DSC control unit. If there is insufficient brake fluid, this will be indicated in the instrument cluster by the general brake warning lamp lighting up red.

The DSC control unit also communicates with the following control units

DME or DDE: Digital engine electronics or digital diesel electronics The DME or DDE, as applicable, controls engine adaptation (for example, reduction in engine output to prevent spin at the driven wheels). The DME or DDE also receives the converted wheel speed signal from the rear right wheel. This signal is used to check the plausibility of engine misfires (DME). The signal on the PT-CAN is redundant.
RLS: Rain-light sensor The signal from the rain-light sensor is used to brake the brake discs dry on a wet road surface. In addition, it is important for a wiper stage to be switched on. E60, E61, E63, E64 The rain-light sensor supplies the signal on the CAN bus. E83 The rain-light sensor supplies the signal on the K-bus. E90, E91, E92 The rain-light sensor is connected to the roof control panel (FZD) via the LIN bus.
CAS and M-ASK/CCC: Car Access System and multi-audio system controller/Car Communication Computer The CAS control unit and M-ASK/CCC receive the converted wheel speed signal from the rear left wheel. Both these control units use this signal to ascertain whether the car is moving or at a standstill.
SGM: Safety and gateway module E60, E61, E63, E64 up to 09/2005 The SGM is the data interface (= gateway) between: PT-CAN K-CAN Byteflight Diagnosis wire to diagnosis socket
KGM: Body gateway module E60, E61, E63, E64 from 09/2005 The vehicle electrical system was changed from 09/2005. As a result of the change, several control units were discontinued and some control unit functions were integrated into new control units. The new body gateway module supersedes the safety and gateway module (SGM) previously fitted. The KGM is the data interface (= gateway) between: PT-CAN K-CAN Diagnosis wire to diagnosis socket
JBE: Junction box electronics E90, E91 from 09/2005 and E92 from 06/2006 The JBE is the data interface (= gateway) between: PT-CAN K-CAN Diagnosis wire to diagnosis socket Signals from the chassis CAN (F-CAN) are simply looped through.
ACC: Active Cruise Control DSC receives requests from Active Cruise Control (ACC) via the PT-CAN. In response, DSC reduces speed by applying the brakes at all four wheels.
LM: Light module E60, E61, E63, E64 As required by law, the brake lights are activated in the event of automatic braking when the Electronically Controlled Deceleration function (ECD) is triggered by the ACC. To do this, a signal must be sent from the DSC to the light module (LM) via the K-CAN.
FRM: Footwell module E90, E91, E92 As required by law, the brake lights are activated in the event of automatic braking when the Electronically Controlled Deceleration function (ECD) is triggered by the ACC. To do this, a signal must be sent from the DSC to the footwell module via the PT-CAN.
KOMBI: Instrument cluster The DSC control unit actuates the indicator and warning lights for the individual DSC functions via the instrument cluster (signal via CAN bus). E83 The instrument cluster is the data interface (= gateway) between: PT-CAN K-bus
EGS: Electronic gearbox control (vehicles with automatic transmission) The transmission control (EGS) receives the wheel-speed signals via the PT-CAN. The gearbox controller responds by adapting the gearshift characteristics for cornering and ascents. In addition, the gearshift characteristics are adapted to winter conditions (high wheel slip). Moreover, gearshifts are suppressed during DSC control.
CID and CON: Central Information Display and controller The detailed texts for the Check-Control messages are shown in the Central Information Display (CID). CID and controller are also used to initialize the Run Flat Indicator (RPA). With xDrive an additional function can be activated to reduce speed when driving downhill: Hill descent control (HDC)
TCU or ULF: Telephone control unit with GPS antenna If the car is not fitted with a navigation system , the telephone control unit receives the converted wheel speed signals from the front left and right wheels. The telephone control unit uses these signals to pinpoint the car's position by dead reckoning.
GM: General module E83 The general module supplies input signals with respect to terminal control.

System functions

The dynamic stability control system (DSC) controls longitudinal and transverse dynamics by means of engine and brake system intervention.

DSC 8Plus includes the following new functions.

Brake Standby through pre-tensioning of the brakes in an emergency
Brake disc drying on wet roads
Fading compensation
Soft stop when braking to standstill (not on BMW 3-Series all-wheel drive or E83)
Start-off assistant

DSC 8Plus includes the following familiar functions.

ABS: Anti-lock braking system
EBV: Electronic brake force distribution
CBC: Cornering brake control
DTC: Dynamic traction control
ASC: Automatic stability control
MSR: Engine drag torque control
DBC: Dynamic brake control
Trailer stabilization control
HDC: Hill descent control
ECD: Electronically controlled deceleration (only in conjunction with ACC)
All-wheel control
RPA: Run Flat Indicator
CBS: Condition Based Service

Brake Standby through pre-tensioning of the brakes in an emergency

Pre-tensioning the brakes shortens the brakes' response time.

If the accelerator pedal is rapidly released (accelerator pedal angle), the brakes are immediately pretensioned.

DSC generates a low brake pressure without a measurable deceleration taking place.

The clearance between the brake pads and brake discs is eliminated. If the brakes are not applied within half a second, the brake pressure that was generated early is reduced again. The pre-tensioning of the brakes depends is active at speeds greater than 70 km/h.

Brake disc drying on wet roads

Braking dry removes moisture that gathers on the brake discs during journeys on wet roads or in rain.

The brake pads are lightly applied. This function also shortens the brakes' response time.

Depending on the signal from the rain sensor and the position of the wiper switch, DSC cyclically generates a low brake pressure. This creates no measurable deceleration on the vehicle. The brake pads are cyclically applied. This means that the brake disc are regularly wiped down. How often and how long the brake pads are applied depends on

The intensity of the rain, e.g. the speed of the windscreen wiper
Road speed greater than 70 km/h

Fading compensation

Fading means: braking effect deteriorates as a result of high brake-disc temperatures.

If fading is detected, DSC reacts by increasing the brake pressure above that specified by the driver.

At very high brake-disc temperatures, fading compensation is indicated by the following

General brake warning lamp lighting up yellow
Check-Control symbol in LCD display in instrument cluster lighting up yellow (not E83)

DSC detects fading as follows: DSC compares the current vehicle deceleration with a nominal value based on the current brake pressure.

DSC increases brake pressure until the nominal deceleration is achieved or until all wheels are subject to ABS control. The process is ended when the brake pedal is no longer depressed or when the speed drops below a certain threshold.

Soft stop when braking to standstill (not on BMW 3-Series all-wheel drive or E83)

Soft stop prevents the vehicle from jolting to a stop (e.g. with an inexperienced driver).

When the vehicle is braked to a standstill, there is no uncomfortable jerk (causing the occupants to "lurch" forward). DSC calculates the moment that standstill can be expected from the current road speed and deceleration.

Just before standstill is achieved, the brake pressure on the rear axle is reduced so that the vehicle stops with practically no jerking.

Soft stop is only active for light braking, so that the shortest possible stopping distance can still be achieved in emergency braking situations.

Start-off assistant

When pulling away on a slope, it is necessary to move your foot from the brake pedal to the accelerator pedal. The start-off assistant prevents the vehicle from rolling downhill in the following situations

uphill in forward gear
uphill in reverse gear

It does this by maintaining the brake pressure needed to hold the vehicle. The gradient is recorded by the longitudinal-acceleration sensor in the DSC control unit.

The braking torque and engine torque needed is calculated from the gradient. When pulling away is detected, brake pressure is reduced as soon as the available engine torque is sufficient to move the vehicle in the direction required. The start-off assistant is deactivated when the parking brake is applied. If no move is made to pull away within 2 seconds of the brake pedal being released, the start-off assistant will be deactivated.

DSC: Dynamic Stability Control

Dynamic Stability Control (DSC) detects the current status of the vehicle by evaluating the sensor signals.

This status is compared with the nominal values derived from a computational model.

In this way, the system recognizes incipient instabilities.

The vehicle is stabilized as soon as a deviation overshoots the control threshold stored in the DSC control unit. Stabilization (within the limits imposed by the laws of physics) is achieved by reducing engine power and by braking individual wheels.

DSC actions are superimposed on the ABS and ASC functions.

The DSC function can be deactivated by means of the DTC button.

ABS: Anti-lock braking system

The anti-lock braking system (ABS) stops the wheels locking during braking.

Advantage: Shorter stopping distances, the car retains its directional stability and remains steerable.

Brake pressure is regulated at all wheels to ensure that each wheel runs in the best possible slip range.

When this happens, slip is controlled so that the maximum possible braking and lateral stability forces can be transmitted.

ABS alone is available for braking if a sensor for DSC fails or if a bus fault occurs (PT-CAN and chassis CAN). ABS is the surviving safety function in circumstances in which DSC control is no longer possible.

EBV: Electronic brake force distribution

Electronic brake force distribution (EBV) is a component of the ABS. EBV regulates the brake force distribution between the front and rear axles, depending on vehicle load.

Advantage: Regardless of the load state of the vehicle, the best possible braking distance is achieved while driving stability is maintained. The brake pads wear more evenly.

If the ABS fails, the EBV function is sustained for as long as possible.

The signals from at least two wheel-speed sensors are needed for the EBV function.

CBC: Cornering brake control

Cornering brake control (CBC) is an extension of ABS. CBC increases driving stability when the brakes are applied as the car corners ("cornering logic").

Advantage: Optimum driving stability if brakes are partially applied when cornering.

The shift in wheel loads as the car corners (the onset of this phenomenon requires no more than light application of the brakes) can result in a reduction in handling stability. If required, CBC generates a stabilizing load moment when the brakes are applied lightly outside the ABS intervention range.

DTC: Dynamic traction control

DTC is a version of DSC that has been optimized for forward momentum in certain road conditions.

Dynamic traction control (DTC) offers better traction as a trade-off against a reduction in stability in some circumstances. Consequently, its use should be reserved for exceptional conditions. It is advisable to briefly activate DTC in the following exceptional circumstances

To rock the vehicle free or pull away in deep snow or on a loose surface.
When driving on snowy uphill stretches, in slush and on roads that have not been cleared
When driving with snow chains.

The DTC function approximates to that of DSC with a slightly modified control strategy.

DTC can be activated by deactivating DSC (DTC button). DTC intervenes in the braking actions to imitate the function of a conventional differential lock. This effect of this is to increase the input torque on those wheels that are on a higher-friction surface.

Advantage: Higher traction is available with DTC.

Vehicle stabilization intervention (e.g. reduced power output) is made slightly later than with DSC. In certain situation, the driver has to intervene more intensively himself to stabilize the vehicle.

ASC: Automatic stability control

Automatic stability control (ASC) prevents the wheels spinning during acceleration by intervention in brake and engine operations.

Advantage: More traction and better driving stability.

If the wheels on the driven axle have a different level of grip, the wheel that tends to spin is braked. If necessary, the engine's power output is also reduced.

MSR: Engine drag torque control

The engine drag torque control (MSR) counteracts the tendency of the wheels to lock on smooth surfaces. The engine's drag torque generated by downshifts or abrupt load changes can lock the driven wheels (especially on surfaces with a low coefficient of friction).

The wheel-speed sensors tell MSR as soon as the wheels are about to lock. MSR then briefly reduces the engine's drag torque by opening the throttle slightly.

Advantage: The drive wheels retain their lateral stability in overrun mode.

DBC: Dynamic brake control

Dynamic brake control (DBC) assists in emergency braking situations by automatically increasing the brake pressure.

Advantage: Shortest possible braking distances in emergency braking situations by achieving ABS regulation on all four wheels.

The brake pedal is frequently not depressed strongly enough in emergency braking situations. ABS regulation is then not activated.

In the following situations, the return pump increases the brake pressure until ABS regulation is activated

When the brake pedal is rapidly depressed with insufficient pedal force
When the brake pedal is depressed slowly and the demand for deceleration is subsequently high, after one wheel reaches the ABS control threshold. Which wheel locks first depends on load and coefficient of friction of the road surface. Example of a typical situation: The traffic slows, making light braking necessary at first, but then demands as short a stopping distance as possible.

Trailer stabilization control

Trailer stabilizing control detects when a trailer is rocking about its vertical axis. The system functions at a speed of about 65 km/h when the trailer socket is in use.

With the aid of the DSC sensors, Dynamic Stability Control (DSC) monitors the vehicle's yaw behavior.

If the trailer's rocking motion exceeds the limit, the engine output is reduced. In addition, DSC brakes all four wheels automatically.

If DSC is deactivated or faulty, then the trailer stabilizing control does not work either.

HDC: Hill Descent Control

Hill descent control (HDC) is an automatic cruise control system on all-wheel-drive vehicles for driving downhill.

HDC automatically reduces the vehicle's speed. The brakes are applied on all four wheels to reduce road speed to just above walking pace. This allows stable downhill driving on steep and slippery surfaces.

HDC holds this speed constant (all DSC functions remain active).

The vehicle's road speed can be continuously varied within the specified values by depressing the accelerator pedal and brake pedal or the cruise-control system steering-column stalk.

E60, E61

HDC can be switched on and off at the Central Information Display (CID): "Settings" menu and "Vehicle settings" submenu.

At the factory, HDC is assigned to the lower freely programmable button on the multi-function steering wheel.

E83 and E90, E91, E92

HDC can be activated and deactivated via a separate button in the SZM (centre console switch cluster).

Electronically controlled deceleration

The electronically controlled deceleration (ECD) reacts to a demand from Active Cruise Control (ACC).

When the ACC system requires deceleration, DSC responds by applying the disc brakes on all four wheels (maximum rate of retardation 2.5 m/s 2 ).

When the car is on a decent with the speed preset by the driver, ECD automatically applies the brakes in order to keep the car's speed constant at the preset value.

When the brakes are applied automatically in this way, the bake lights are activated in accordance with the requirements of road-safety legislation.

The light module does not activate the brake lights unless the vehicle's rate of deceleration is greater than 1m/s 2 .

This prevents the brake lights from flickering on and off.

All-wheel control

Dynamic Stability Control (DSC) specifies the nominal value for xDrive all-wheel control. The DSC control unit calculates the locking moment for the multi-plate clutch in the transfer box.

The nominal value depends on the vehicle's tendency to oversteer or understeer and wheelslip. The nominal value is sent via the PT-CAN to the VTG control unit.

The VTG control unit reports the actual set locking moment back to the DSC control unit.

The DSC control unit calculates the locking torque for the multi-plate clutch as follows

Pre-activation = driver's command
Driving dynamic control
Detection of different tire rolling circumferences

RPA: Run Flat Indicator

The Run Flat Indicator (RPA) is not a dynamic driving control function.

RPA is integrated into the DSC control unit as 4 wheel-speed signals are needed for this function.

By comparing the speed signals for all four wheels, the system detects differences in rolling circumference at the individual wheels. This enables a gradual drop in pressure to be detected.

CBS: Condition Based Service

CBS is not a driving dynamic function.

Condition Based Service, as the name suggests, is a means of ensuring that the car is serviced as and when necessary. CBS comprises various maintenance operations, e.g. engine oil, spark plugs and brake pads.

The remaining distance for the front and back brake pads are calculated separately in the DSC control unit.

When making the calculation, the condition of the brake pad wear sensors is taken into account (reference point at 6 mm and 4 mm).

Operation

E60, E61, E63, E64 and E83 The DTC button is located in the centre console switch cluster (SZM).
E90, E91, E92 The DTC button is located between the central air vents in the instrument panel.

The DTC button has 2 functions that can be set by pressing the button for different lengths of time.

Press button	Function	Remarks
Short < 3 seconds	DTC function activated.	DTC indicator light on. DSC indicator and warning light on.
Long > 3 seconds	DSC is completely deactivated	DSC indicator and warning light on. This mode is intended for service work (e.g. brake dynamometer).

DTC BUTTON FUNCTION CHART

Note. Reactivating DSC

Briefly pressing the button again reactivates the DSC function. The DSC indicator and warning light goes out (unless a fault has developed in the system).

If the DTC button is pressed for longer than 10 seconds (e.g. by a handbag on the centre console), DSC will recognize an operating error. The DSC function remains active and cannot be deactivated until the ignition has been switched off and on again.

Preconditions for activation

DSC is in ready mode after each engine start.

Scheme 137

Scheme 137: Dynamic Stability Control Mk60E5: E85, E86, E87, E90, E91, E92, E93

BMW 3-Series vehicles with 6-cylinder engine are equipped as standard with Dynamic Stability Control Mk60E5. This version is an advanced development of DSC Mk60E used on the E87. On the DSC Mk60E in the E87, the brake pressure sensor was integrated in the DSC unit (compared to the DSC Mk60).

The DSC Mk60E is also fitted on E90/E91 vehicles with 4-cylinder engine.

The supplier for both DSC Mk60E and DSC Mk60E5: Continental Teves.

Further launch dates for DSC Mk60E5

From 09/2005 in the E87, only on vehicles with 6-cylinder engine
From 01/2006 in the E85
From 04/2006 in the E86

Note. Vehicles with all-wheel drive (E90, E91, E92)

These vehicles are equipped as standard with DSC 8Plus.

New features of the DSC Mk60E5

E92 from 06/2006 E90, E91 from 09/2006 and E93 from 12/2006: The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit. LDM = "longitudinal dynamics management"
Solenoid valves with variable map for flow rate: so-called "analogised" solenoid valves (distribution valves and inlet valves)
5 brake pressure sensors integrated in the new DSC unit
4 active wheel-speed sensors with wheel direction recognition (only E87 with 6-cylinder engine, E90, E91, E92, E93)
1 longitudinal-acceleration sensor on the board of the DSC control unit E85, E86: the longitudinal-acceleration sensor is integrated in the DSC sensor.
DSC sensor taken from the E87, with redundant signals on vehicles with Active Steering (2x rate of yaw, 2x lateral acceleration)
Additional functions of DSC

DSC is a driving stabilization system. DSC has the following tasks/advantages

DSC optimizes driving stability when puling away, accelerating and braking, and when coasting.
DSC recognizes and reduces unstable driving conditions such as understeering or oversteering.
DSC improves traction (especially with DTC: Dynamic Traction Control)

Within the limitations of the laws of physics, DSC helps to keep the vehicle on a safe course.

To do this, DSC must know the following parameters of driving dynamics

Yaw rate as a measure of rotary movement of the vehicle around the vertical axis
Lateral acceleration
Road speed
Longitudinal acceleration

In addition, the driver's intentions are recognized from the following factors: Steering angle, brake pressure and throttle setting, which the driver sets via the accelerator pedal. These values are used top calculate an actual condition in which the vehicle is currently moving. The actual condition is compared to the value calculated by the DSC control unit. If the actual value differs from the calculated value, DSC is activated and initiates brake actions and/or engine control functions.

Advantages

DSC counters all dynamically unstable driving conditions. This means DSC brings about maximum active safety within the physical limits. DSC thus enhances driving comfort by allowing more relaxed driving.

The following components are described for the Dynamic Stability Control (DSC)

Inlet valves and distribution valves These solenoid valves used to be digitally actuated: either OPEN or CLOSED. The inlet valves for the wheel brakes and distribution valves are actuated in such a way that the flow rate is variably controlled. Because these solenoid valves work like analogue solenoid valves, they are known as "analogised" solenoid valves. The analogised solenoid valves allow DSC to realize additional functions.
4 active wheel-speed sensors E87 with 6-cylinder engine, E90, E91, E92, E93 The active wheel-speed sensors measure the speed of the individual wheels. This type of sensor also recognizes the direction of rotation of the wheels.
DSC sensor The DSC sensor measures the rotation of the vehicle around the vertical axis (yaw rate) and the lateral acceleration of the vehicle. E85, E86 The longitudinal-acceleration sensor is part of the DSC sensor. On vehicles with Active Steering, a DSC sensor is installed with redundant sensor system (i.e.. 2 signals for yaw rate and 2 signals for lateral acceleration).
DSC unit The DSC unit consists of the hydraulic unit and the DSC control unit. All 5 brake pressure sensors are integrated into the valve block of the DSC unit. The board of the DSC control unit also holds a longitudinal-acceleration sensor. E85, E86 The longitudinal-acceleration sensor is not part of the DSC unit but rather part of the DSC sensor.
Steering-angle sensor E85, E86 The steering-angle sensor uses sliding contacts to measure the angle of rotation of the steering wheel. E87, E90, E91, E92, E93 The steering-angle sensor optically measures the angle of rotation of the steering wheel.
DTC button E85, E86 The DTC button is located in the SZM (centre console switch cluster). E87, E90, E91, E92, E93 The DTC button is located in the centre console between the central air vents. The DTC button has 3 switching states: DSC operational (standard setting) DTC operational DSC and DTC completely deactivated

Additional input signals from the following components

Brake-fluid-level switch If the brake fluid level is too low, this will be detected (via a reed contact in the expansion tank) and an appropriate message sent to the DSC control unit. DSC is deactivated if there is insufficient brake fluid. There would otherwise be a risk of air being drawn into the brake system.
Brake light switch Together with the signals from the brake pressure sensors, braking actions are recognized.
Parking brake warning switch DSC will recognize skidding that has been deliberately initiated by the driver. Regulation will not take place. Reason: a handbrake turn should remain technically possible.

DSC system functions

DSC uses brake actions and engine intervention to influence longitudinal and lateral dynamics.

DSC comprises numerous functions.

Functions familiar from current DSC

ABS: Anti-lock braking system
EBV: Electronic brake force distribution
CBC: Cornering Brake Control
ASC: Automatic stability control
DTC: Dynamic traction control
MSR: Engine drag torque control
DBC: Dynamic brake control
RPA: Run Flat Indicator (not a driving dynamic control function)
CBS: Condition Based Service (not a driving dynamic control function)

New functions for DSC Mk60E5

Brake Standby through pre-tensioning of the brakes in an emergency
Brake disc drying on wet roads
Fading compensation
Soft stop when braking to standstill (only E87 with 6-cylinder engine, E90, E91, E92, E93)
Start-off assistant
Adapted interface for cruise control with brake function (only E90, E91, E92, E93)
Adapted interface for active cruise control (only E90, E91, E92, E93)
Yaw-moment compensation via active steering (only E87 with 6-cylinder engine, E90, E91, E92, E93)

ABS prevents the wheels from locking when the brakes are applied.

Advantage: Optimum utilization of road surface friction - the vehicle remains stable and steerable.

Brake pressure is regulated at all wheels to ensure that each wheel runs with optimum slip.

When this happens, slip is controlled so that the maximum possible braking and lateral stability forces can be transmitted.

EBV is a component of ABS and controls the brake force distribution between the front and rear wheels.

Advantage: Regardless of the load state of the vehicle, the best possible braking distance is achieved while driving stability is maintained.

Modern vehicles have relatively large brakes on the rear axle to shorten braking distances. To prevent the rear wheels from being overbraked in certain driving situations, EBV permanently monitors slip. EBV controls rear axle slip in dependence of the front axle.

CBC is an extension of ABS. CBC enhances driving stability if the brakes are applied when cornering.

Advantage: If the brakes are applied in a corner, optimum brake force distribution ensures optimum tracking stability.

When cornering, even very light braking can shift the axle-load distribution to the left or right so that driving stability is impaired. If required, CBC generates a stabilizing load moment when the brakes are applied lightly outside the ABS intervention range.

ASC prevents the wheels from spinning when the vehicle is accelerating.

Advantage: Improved traction. The vehicle remains stable.

If one of the wheels of the drive axle is on a high-grip surface and the other is on a slippery surface, the wheel tending to skid is braked.

ASC also intervenes in the engine control (to reduce the ignition angle, injection quantity, throttle valve setting).

DTC is a version of DSC that has been optimized for forward momentum in certain road conditions. Dynamic traction control (DTC) offers better traction as a trade-off against a reduction in stability in some circumstances. Consequently, its use should be reserved for exceptional conditions. It is advisable to briefly activate DTC in the following exceptional circumstances

To rock the vehicle free or pull away in deep snow or on a loose surface.
When driving on snowy uphill stretches, in slush and on roads that have not been cleared.
When driving with snow chains.

The DTC function approximates to that of DSC with a slightly modified control strategy.

Advantage: Higher traction is available with DTC.

The drive wheels are able to lock if a lower gear is selected of load is abruptly changed on a slippery road surface.

Engine drag torque control provides protection against locking drive wheels.

Advantage: The drive wheels retain their lateral stability in overrun mode.

The wheel speed sensors tell MSR as soon as the wheels are about to lock. MSR then briefly reduces the engine's drag torque by opening the throttle slightly.

DBC supports the driver in emergency braking situations. It does this by automatically increasing braking pressure when the brake pedal is not depressed with sufficient force.

Advantage: Shortest possible braking distances in emergency braking situations by achieving ABS regulation on all four wheels.

The brake pedal is frequently not depressed strongly enough in emergency braking situations. The ABS feedback control range is not reached (or not on all 4 wheels).

The return pump increases the brake pressure until ABS regulation is activated

If the brake pedal is depressed quickly with insufficient pedal pressure (recognized from the signal from the brake pressure sensors)
If the brake pedal is depressed slowly and then with greater braking deceleration than necessary (recognized from the signal from the brake pressure sensors), when both front wheels have reached the ABS control threshold.

Example of a typical situation

The traffic slows, making light braking necessary at first, but then demands as short a stopping distance as possible.

RPA is not a driving dynamic function.

DSC uses the Run Flat Indicator (RPA) to monitor the tire pressure throughout the journey.

The RPA records the wheel speeds using the wheel-speed sensors of the Dynamic Stability Control (DSC). The RPA compares the speeds of the individual wheels with the average speed. In this way the RPA is able to detect a loss of tire pressure.

The RPA detects a drop in pressure below about 30 % ± 10 % of the initial value. The RPA indicator and warning light indicates a drop in tire pressure.

The RPA will indicate this after just a short distance, as a rule after a few minutes, from a certain minimum speed (e.g. 25 km/h) up to the permissible top speed.

Initialization is started manually. Then (after a journey has started), initialization runs automatically. In other words, the circumference of individual tires are recorded and evaluated.

The initialization phase lasts approx. 5 to 15 minutes for the individual speed ranges.

CBS is not a driving dynamic function.

Condition Based Service, as the name suggests, is a means of ensuring that the car is serviced as and when necessary. CBS comprises various maintenance operations, e.g. engine oil and brake pads.

The remaining distance for the front and back brake pads are calculated separately in the DSC control unit.

When making the calculation, the condition of the brake pad wear sensors is taken into account (reference point at 6 mm and 4 mm).

Pre-tensioning the brakes shortens the brakes' response time.

If the accelerator pedal is rapidly released (accelerator pedal angle), the brakes are immediately pretensioned. DSC generates a low braking pressure through the "analogised" solenoid valves, without creating any measurable deceleration of the vehicle. The working clearance between the brake pads and brake disks is equalized. If the brakes are not applied within a certain time, this preliminary brake pressure is cancelled. The early pre-tensioning of the brake pads is active at road speeds greater than 70 km/h.

Braking dry removes moisture that gathers on the brake discs during journeys on wet roads or in rain. The brake pads are lightly applied. This function also shortens the brakes' response time.

The intensity of the rain, e.g. the speed of the windscreen wiper
Road speed greater than 70 km/h

Fading means: braking effect deteriorates as a result of high brake-disc temperatures.

If fading is detected, DSC reacts by increasing the brake pressure above that specified by the driver.

At very high brake-disc temperatures, fading compensation is indicated by the following

General brake warning lamp lighting up yellow
Check-Control symbol in LCD display in instrument cluster lighting up yellow

DSC detects fading as follows: DSC compares the current vehicle deceleration with a nominal value based on the current brake pressure. DSC increases brake pressure until the nominal deceleration is achieved or until all wheels are subject to ABS control. The process is ended when the brake pedal is no longer depressed or when the speed drops below a certain threshold.

Soft stop when braking to standstill (only E87 with 6-cylinder engine, E90, E91, E92, E93)

Soft stop prevents the vehicle from jolting to a stop (e.g. with an inexperienced driver).

Just before standstill is achieved, the brake pressure on the rear axle is reduced so that the vehicle stops with practically no jerking. Soft stop is only active for light braking, so that the shortest possible stopping distance can still be achieved in emergency braking situations.

The start-off assistant prevents the vehicle from moving unexpectedly when the driver moves his foot from the brake pedal to the accelerator pedal (e.g. when pulling away on a hill)

uphill in forward gear
uphill in reverse gear

It does this by maintaining the brake pressure needed to hold the vehicle.

The gradient is recorded by the longitudinal-acceleration sensor in the DSC control unit. From the gradient, the necessary braking torque or engine torque is calculated. When pulling away is detected, brake pressure is reduced as soon as the available engine torque is sufficient to move the vehicle in the direction required. The start-off assistant is deactivated when the parking brake is applied. If no move is made to pull away within 2 seconds of the brake pedal being released, the start-off assistant will be deactivated.

Adapted interface for option 544 "Cruise control with brake function"

E92 from 06/2006 and
E90, E91 from 09/2006 (up to 09/2006: "cruise control with brake function" always with LDM) and
E93 from 12/2006

The LDM control unit is no longer fitted on vehicles with option 544 "Cruise control with brake function". Because of a software modification in the DSC control unit (DSC Mk60E5), the DSC control unit assumes control of the functions of the LDM control unit. LDM = "longitudinal dynamics management"

Adapted interface for option 541 "active cruise control"

E90, E91, E92, E93 ("active cruise control" always with LDM)

The interface between Dynamic Stability Control (DSC) and active cruise control (ACC) has been adapted with the longitudinal dynamic management system. The software in the DSC control unit evaluates the demands of the ACC even more quickly. Pressure at the wheel brakes can be built up or reduced more efficiently from the point of view of vehicle deceleration and comfort.

The longitudinal dynamic management (LDM control unit) transmits the signals from the active cruise control. Part of the ACC software is integrated in the LDM control unit.

Yaw-moment compensation via Active Steering

E87 with 6-cylinder engine, E90, E91, E92, E93

Active Steering offers an additional function for driving stabilization

With conventional systems, the driver has to actively steer the vehicle in a straight line if the brakes are applied on a road surface with non-uniform traction levels ("μ-split"). Counter steering keeps the vehicle in its track and helps to achieve acceptable braking distances.

For such situations, Active Steering actuates these active steering actions. The vehicle is stabilized. At the same time, a shorter braking distance is achieved.

The DSC control unit calculates the yaw rate with the brake pressure sensors on the front axle.

The DSC control unit transmits to the Active Steering control unit the yaw-moment compensation correction angle needed for stabilization.

DSC is activated after every engine start.

Brakes - Service Techniques BMW M3 E90