Abs/traction Control - Overview (e46) BMW M3 E46

MK20 EI ASC

Model: E46/4

Production Dates: 6/98 to 6/99

ASC was standard equipment on both the 1999 323i and 328i Models. The Teves - Mark 20 EI system is used for the E46. The theory/operation of the slip control system is unchanged from the previous ASC system. The major changes of the Mark 20 El are

Scheme 53

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1. The electronic control module is integrated into the hydraulic unit.
2. The throttle reduction operation is carried out through the DME activation of the MDK motor.
3. The ASC control module communicates with the AGS and DME control modules over the CAN Bus.

The Mark 20 EI system includes the Cornering Brake Control (CBC) utilized in the Bosch ASC 5 system. This feature reduces pressure build-up on the inside rear brake circuit while cornering, if the threshold values for activation are exceeded.

Scheme 55

Electronic Brake Proportioning (EBV)

A new feature of the Mark 20 EI system is the Electronic distribution of the braking force (EBV). This feature will adjust the braking force to the rear wheels based on the vehicles loading to maximize the braking force at all wheels.

The control module monitors the wheel speed sensor inputs, when the brakes are applied, to determine vehicle loading. The control module compares the rate at which the front and rear axles are slowing down.

If the rear axle is slowing at a rate similar to the front it indicates that the vehicle is loaded and more braking force can be applied to the rear calipers to stop the vehicle.

If the decel rate of the rear wheels is far less than the front, it indicates a lightly loaded vehicle. At this point, if the same braking force were applied to the front and rear axles, the vehicle would become unstable.

If this difference exceeds the threshold values programmed in the control module, EBV is activated. The control module will cycle the inlet valves to the rear brakes to regulate the braking force.

Diagnosis

Diagnosis of the slip control system is carried out with the DIS or MoDiC using the fault symptom driven troubleshooting procedures.

DSC III MK20

Model: E46 all versions except all-wheel drive

Production Dates: 6/99 to 9/00

Introduction

The DSC III system was introduced for the E46, beginning with Model Year 2000 production (E46/2: 6/99, E46/4: 9/99). The system is similar to the DSC III used on the E38 and E39 vehicles, however it is manufactured by Teves for use in the E46.

The system incorporates all of the features of the previous Teves slip control system and adds the lateral dynamic control of the DSC III system already installed on the E38/E39s.

The Teves DSC system is designed to maintain the lateral locating forces for the following

1. ABS braking control
2. ASC +T traction control
3. DSC - Dynamic Stability Control for oversteer and understeer conditions

System Overview

The E46 DSC III system consists of the following components

1. Control module/Hydraulic Unit (combined)
2. Four wheel speed sensors
3. Charge pump
4. Tandem Brake Master Cylinder
5. Steering Angle Sensor
6. Yaw Rate Sensor
7. Lateral Acceleration Sensor
8. Two Brake Pressure Sensors
9. Brake Fluid Level Switch
10. DSC Button
11. DSC Warning Indicator
12. CAN Interface (DME/AGS)

DSC Control Overview

The Teves DSC system maintains the lateral location forces during all phases of operation through

1. ABS - Hydraulic intervention preventing the wheels from locking during hard braking
2. ASC +T - Engine drive torque reduction and/or hydraulic intervention on the drive wheels to ensure straight line traction (acceleration - driving and deceleration)
3. DSC - Engine drive torque reduction and/or hydraulic intervention on any wheel brake during cornering to minimize oversteer and understeer conditions

DSC control can aid the driver in controlling the vehicle while driving but can not overcome the laws of physics if the vehicle is being driven beyond the range of DSC control.

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Control Module/Hydraulic Unit

The control module is installed in the engine compartment, on the right side, in the battery well.

Both the control module and the hydraulic unit are replaceable as separate components.

All processing functions for ABS/ASC or DSC regulating functions are carried out in the one control module. The module is linked to the CAN bus for communication with the DME and AGS control modules. Additionally the CAN bus is used for communication with the steering angle sensor and for illumination of the ABS and DSC indicator lamps in the instrument cluster.

The hydraulic unit consists of the following

Scheme 58

1. Four inlet solenoids
2. Four outlet solenoids
3. Two changeover solenoids
4. Two charge solenoids

Wheel Speed Sensors

The E46 DSC III system uses the same inductive wheel speed sensors from the ASC system.

Scheme 59

Brake Light Switch

The brake light input signal is used by the control module to interrupt an ASC regulation control if the driver steps on the brakes during its operation.

This interruption does not take place during DSC regulation.

Brake Fluid Level Switch

Fluid level switch is incorporated into the brake master cylinder reservoir. If the fluid level is correct, the switch provides a ground signal to the DCS control module.

If the fluid level drops below the specified level, the switch opens and the ASC/DSC functions are switched off.

Scheme 60

DSC Button

The DSC system comes on every time the vehicle is switched on. The DSC button can be used to switch the system off. The warning indicator lamp comes on when the system is manually switched off

Scheme 61

Steering Angle Sensor

The steering angle sensor is mounted at the bottom of the steering column, in front of the flexible coupling. It utilizes two potentiometers to determine steering angle and the rate of steering change. These signals are processed in the steering angle sensor and a digital output signal is passed over the CAN bus to the DSC control module.

The sensor requires calibration after repairs to the steering or suspension system. The sensor is calibrated using the DIS or MoDiC. Once calibrated, the sensor sends an ID number to the DSC control module. The ID provides confirmation to the module that the angle sensor is properly calibrated.

Installing a new sensor or exchanging sensors with another vehicle will require that this calibration procedure is carried out.

Scheme 62

CAN Interface

The DSC control module communicates over the CAN line for the following

Scheme 63

1. Steering angle from the steering angle sensor
2. Engine control module for engine intervention
3. Transmission control module for shift intervention
4. Instrument cluster for illumination of the warning indicator lamps

Rotation Rate Sensor

The rotational rate sensor is mounted under the driver's seat. It provides a signal to the DSC control module that corresponds to the vehicles rotational speed around its axis (yaw speed).

The sensor receives its operating power (5 volts) from the DSC control module and provides an output voltage of approx. 0.25 to 4.65 volts depending on the amount of yaw exerted on the vehicle.

The sensor operates on the Coriolis effect to produce the output voltage. The element of the sensor is a micromechanical double quartz tuning fork. A frequency of 11 Hertz is applied to one side of the fork and as the vehicle turns on its axis, vibrations are induced into the tips at the other end.

The sensor processes the signals produced by the fork and produces an analog voltage signal that is proportional to the amount of yaw.

Based on the control module's programming parameters, the DSC will activate a DSC regulation cycle to ensure that the vehicle remains stable under all driving conditions.

Scheme 64

Lateral Acceleration Sensor

The lateral acceleration sensor is mounted in the left "A" pillar. The sensor provides the DSC control module with an input signal that corresponds to the degree of lateral acceleration ("G" forces) acting on the vehicle.

The sensor is a capacitive type with two capacitive plates (one fixed and one moving).

Under the effect of lateral acceleration, the one plate moves in relation to the fixed plate.

This results in a voltage signal being produced in proportion to the degree of lateral acceleration.

The voltage signal output of the sensor to the DSC control module ranges from 0.5 to 4.5 volts. When the vehicle is stationary, The standing voltage from the sensor is approximately 1.8 volts.

This signal is used in conjunction with the yaw sensor input to determine the degree of DSC regulation required to maintain the vehicles stability.

Scheme 65

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Pre-Charge Pump

The pre-charge pump is installed between the master cylinder and the brake fluid reservoir.

During DSC controlled regulations that involve brake intervention, the pump ensures that the required volume of fluid is available for the hydraulic unit.

When activated, the pre-charge pump draws fluid from the reservoir and delivers it to the master cylinder at a pressure of 10 Bar.

Scheme 67

Master Cylinder/Fluid Reservoir

The master cylinder contains the central valves in both the front and rear brake circuits, Similar to the Bosch DSC system. The central valves allow fluid to transfer during DSC controlled interventions.

The brake fluid reservoir has internal baffles that minimize fluid foaming during controlled interventions. The charge pump pick up is mounted low on the reservoir to prevent air from entering the system during regulation. The fluid level switch will signal the control module to cancel DSC regulation if the fluid is below the safety margin level.

Scheme 68

Pressure Sensors

Two pressure sensors are installed on the master cylinder in the outlet ports for the front and rear brake circuits. The sensors provide the DSC control module with an analog voltage signal in proportion to the brake pressure in the master cylinder.

Scheme 69

DSC Hydraulic Operation

Based on the programming of the DSC control module, hydraulic intervention can be activated at any wheel brake as follows

1. ABS regulation for any wheel that is in danger of locking - causing the wheel to skid.
2. ASC regulation for either or both rear wheels to ensure that the optimum traction is applied to the drive wheels
3. DSC regulation for any wheel to correct for dynamic forces that are causing the vehicle to become unstable. The DSC intervention only takes place on one wheel of a corresponding axle.

Depending on the hydraulic intervention required, the charge pump, return pump, change over valves, charging valves, inlet and outlet solenoids are activated to provide

Scheme 70

1. Pressure build up for brake application
2. Pressure hold to slow or stop the wheel
3. Pressure release to allow the wheel to turn

Troubleshooting the E46 TEVES DSC system is carried out using the DIS or MoDiC.

The fault indicators in the instrument panel will illuminate when there is a fault and the system is off line.

Follow the diagnostic procedures as outlined with the tester to troubleshoot the E46 Teves DSC system.

Scheme 71

TEVES DSC III MK60

Model: E46 (except M3 and Xi) and E36/7

Production Date: From 9/00

Purpose of the system

DSC III MK60 is supplied by Continental Teves and supersedes the Teves DSC III MK20 EI system. The MK60 includes all of the features of the previous MK20 EI system and incorporates two additional functions

1. DBC function
2. Modified ADB function

The most important changes from the MK20 EI are

1. Reduction in size of the control unit/hydraulic Unit.
2. Installation of the hydraulic unit close to the master cylinder.
3. Elimination of a pre-charge pump.
4. Magneto resistive wheel speed sensors.

The Teves MK60 system is designed to maintain the vehicles stability during

1. ABS braking regulation
2. ASC+T traction control
3. DSC for oversteer and understeer control

Additional features are also programmed into the control module to enhance driver safety and comfort. These features are

1. CBC Corner Brake Control
2. EBV Electronic Brake Proportioning
3. MSR Engine Drag Torque Regulation
4. ADB Automatic Differential Brake
5. DBS Dynamic Brake System

Scheme 72

System Components

The Teves DSC III MK60 consists of the following components

1. Integrated Control unit/Hydraulic unit with CAN Interface
2. Tandem Master Brake Cylinder
3. Brake Expansion Tank with Fluid Level Reed Contact in Cap
4. 2 Brake Pressure Sensors
5. Brake Light Switch
6. 4 Wheel Speed Sensors (active)
7. Rotation Rate Sensor (yaw)
8. Steering Angle Sensor (LEW)
9. Transverse Acceleration Sensor
10. DSC Button (part of SZM)
11. Instrument cluster Warning indicators
12. Hand brake Switch
13. Wiring Harness

Control Unit/Hydraulic Unit

The MK60 control unit/hydraulic unit is located in the engine compartment on the left side under the brake master cylinder.

Both the control unit and the hydraulic unit are replaceable as separate components.

The pre-charge pump used on previous systems is no longer required. Rapid pressure build up is possible because of the close proximity of the hydraulic unit to the master cylinder and improvements in the design of the return pump.

The control unit/hydraulic unit itself is 20% smaller and lighter than the previous MK20 EI.

Scheme 73

All processing functions for ABS, ASC or DSC are performed by the combined control unit/hydraulic unit. The MK 60 control unit is also responsible for processing the wheel speed signals and providing them to other control units.

The MK60 control unit for MY 2002 incorporates the RDW function into its scope of control, making a separate RDW control unit unnecessary. The operating principle continues to be based on the analysis of wheel speed.

Scheme 74

Scheme 75

The hydraulic unit consists of an aluminum block containing 12 solenoid valves, 2 pressure accumulators and the return pump.

1. 4 inlet solenoid valves (N/O)
2. 4 outlet solenoid valves (N/C)
3. 2 changeover solenoid valves (N/O)
4. 2 Intake solenoid valves (N/C)

The solenoid valving ensures that normal braking is possible in the event of a defective control unit.

In ABS regulation the pump returns fluid back to the master cylinder circuits. In ASC/DSC regulation with brake intervention, the pump is responsible for building up the brake pressure required for the front and rear hydraulic circuits.

Note. N/O= Normally Open N/C= Normally Closed

The MK60 is connected to the CAN bus for communication with the AGS, DME control module, Steering Angle Sensor and the Instrument Cluster.

The CAN bus allows all of the connected control modules to send and receive information and commands.

Communication with the MK60 includes

Scheme 76

1. DME - The DME sends current engine torque. MK60 commands the DME to reduce (ASC/DSC) or raise (MSR) engine torque.
2. AGS - The MK60 commands the AGS to suppress shifts during regulation.
3. LEW - The MK60 receives steering angle information.
4. KOMBI - The MK60 commands the instrument cluster to activate or deactivate the warning lamps.
5. All four wheels speed signals are sent over the CAN bus for use by other modules.

Tandem Master Brake Cylinder

The MK60 system uses a tandem master brake cylinder fitted with central valves as in other DSC master cylinders. The central valves allow fluid to be drawn through the master cylinder during ASC and DSC regulation. The hydraulic circuit is divided front/rear.

An inlet for pre-charge pressure is no longer used since the charge pump has been eliminated from the MK60.

Both brake pressure sensors are mounted on the master cylinder.

Scheme 77

Expansion Tank and Brake Fluid Level Switch

The brake fluid expansion tank has internal baffles that reduce foaming during return pump operation.

The expansion tank includes a pick-up tube for clutch master cylinder fluid supply.

The brake fluid level switch is incorporated into the cap. The switch is a reed contact switch.

If the brake fluid is at a sufficient level, the switch is closed and switched to ground.

Scheme 78

If the fluid level drops below a specified level, the reed contacts open and the MK 60 responds by switching off the ASC/DSC functions.

Normal braking and ABS operation is unaffected.

Brake Pressure Sensors

Two brake pressure sensors are mounted on the master cylinder below the outlet ports for the front and rear brake circuits. The sensors are provided a 5V reference voltage by the MK 60 control unit.

The sensor provides the control unit with an analog signal proportional to brake pressure.

Voltage increases with increasing brake pressure.

Plausibility With Brake Light Switch

The signal input from the brake light switch is compared with the pressure sensor values.

The pressure sensors must not detect more that 5 bar when the BLS is not actuated.

Both signals are used to form a redundant BLS input which is constantly monitored.

Scheme 79

Note. Refer to the Workshop Hints for instructions on initializing the brake pressure sensors.

Brake Light Switch (BLS)

The brake switch is an input to the MK 60 to inform it that the brakes are being applied. If the signal is received during an ASC regulation then brake regulation is interrupted.

Scheme 80

Wheel Speed Sensors (Active)

With the introduction of the Teves DSC III MK60, active wheel speed sensors that operate on the principle of magnetoresistive effect are used for the first time on BMW vehicles.

The sensor element and evaluation module are two separate components within the sensor housing.

Scheme 81

Principle Of Operation Of The Magnetoresistive Sensor

The active sensing of the magnetoresistive sensor is particularly suitable for advanced stability control applications in which sensing at zero or near zero speed is required.

A permanent magnet in the sensor produces a magnetic field with the magnetic field stream at a right angle to the sensing element.

The sensor element is a ferromagnetic alloy that changes its resistance based on the influence of magnetic fields.

As the high portion of the pulse wheel approaches the sensing element, a deflection of the magnetic field stream is created. This causes the resistance to change in the thin film ferromagnetic layer of the sensor element.

Scheme 82

The sensor element is affected by the direction of the magnetic field, not the field strength.

The field strength is not important as long as it is above a certain level. This allows the sensor to tolerate variations in the field strength caused by age, temperature or mechanical tolerances.

The resistance change in the sensor element affects the voltage that is supplied by the evaluation circuit. The small amount of voltage provided to the sensor element is monitored and the voltage changes (1 to 100mV) are converted into current pulses by the evaluation module.

Scheme 83

1. Signal High- 14mA
2. Signal Low- 7mA

The sensor evaluation circuit is supplied 12V by the MK60 control unit. Output voltage from the sensor is approximately 10V. The control unit counts the high and low current pulses to determine the wheel speed signal.

Front sensors are three wire because they have a separate ground wire.

Rear sensors are two wire and use the sensor case as a ground point.

Different sensors are used on the left and right side front axle of the vehicle. The difference comes in the length of the harness.

The connectors are blue to distinguish them apart from the grey connectors used for sensors on the MK20 EI.

The DSC III MK60 uses the same metal pulse wheels used with the MK20 inductive sensors.

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There are two types of sensors used in the rear axle of the E46

1. The short sensor is used on the 325i (any transmission) and 330i automatic.
2. The long sensor is used on the 330i manual transmission version. The Z3 uses the same sensors for the rear axle, left or right.

The Rotation Rate Sensor is mounted on a metal bracket under the drivers seat. The sensor provides information to the MK60 concerning the vehicles speed around its main axis (yaw).

The sensor has a three pin connector with the following connections

1. 5V reference
2. Signal
3. Ground

The sensor receives a reference voltage of 5V from the MK60 control unit and provides a signal output of approximately 0.25 to 4.65V depending on the amount and direction of yaw. If the sensor is defective a constant voltage will be sent to the MK60.

The sensor element is a micro-mechanical double quartz tuning fork. A frequency of 11 Hertz is applied to one side of the fork and as the vehicle turns on it's axis, vibrations are induced on the other end.

The sensor analyzes the signal produced by the fork and produces an analog voltage signal that is proportional to the amount of yaw.

The rotation (yaw) rate is compared to the signal from the Steering Angle Sensor and the Transverse Acceleration Sensor. If physical limits are beginning to be exceeded, the MK60 DSC will begin regulation by engine and brake intervention to attempt to stabilize the vehicle. This is referred to as a GMR regulation.

Scheme 87

The MK60 DSC III for M.Y. 2002 incorporates a combined Rotation rate and Transverse Acceleration Sensor. The Sensor is connected to the MK60 control unit by the CAN bus.

The Z3 version will retain separate sensors until the E36/7 is replaced by the E46/6.

Steering Angle Sensor (LEW)

The Steering Angle Sensor is mounted towards the lower end of the steering column, above the flexible coupling. The LEW consists of a potentiometer and a built in microprocessor. The potentiometer has two pickups offset at 900 to one another. The raw potentiometer signal is processed and converted into a digital signal that is transmitted over the CAN bus to the MK60 DSC III control unit.

Scheme 88

The sensor requires initialization in order to create a zero point default. Once initialized the LEW sends an ID number to the DSC control unit. The ID provides confirmation that the LEW is properly initialized.

The total steering wheel angle is determined by combining the CAN telegram signal, the stored zero point default and the actual number of turns to the wheel. In order to prevent the LEW from loosing count, KL 30 is provided to the sensor and it continues to record even after the ignition has been switched off.

The MK60 DSC III calculates the drivers desired rate of turn from the steering angle signal.

Scheme 89

Note. Refer to the Workshop Hints for instructions on coding and initializing the sensor.

Transverse (Lateral) Acceleration Sensor

The Transverse Acceleration Sensor is mounted in the left "A" pillar behind the driver's foot rest. The sensor provides the MK60 DSC control unit with a signal that corresponds to the degree of transverse acceleration (G forces) acting on the vehicle.

The sensor is a capacitive sensor with two plates. One plate is rigidly mounted, the other plate is mounted on a spring. Under the effect of transverse forces acting on the sensor the distance between the plates changes.

Scheme 90

This change of distance between the plates affects the capacitance of the sensor. The evaluation circuitry converts the signal into an analog voltage that is transmitted to the control unit.

The output signal of the sensor is between the range of 0.5 to 4.5 Volts. This corresponds to -1.5 to 3.5g respectively. When the vehicle is stationary the output is 1.8V.

The transverse acceleration signal is used in the MK60 DSC III control unit along with the rotation rate and steering angle signal to determine if DSC regulation is required to maintain the vehicles stability.

Note. Refer to Workshop Hints for instructions on initializing sensor.

The DSC button is located on the SZM, however the SZM provides no processing, it is simply a housing for the button which is hardwired to the MK60 control unit.

The DSC Button features two functions that can be set by varying the time the button is held down for

BUTTON ACTIVATION REFERENCE CHART

Pressing the button again returns the system to normal status. It is not possible to go directly from one function to the next without first returning to normal status.

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Three warning indicator lamps are arranged in the instrument cluster

1. DSC lamp: Indicates fault in DSC or system disabled by the switch.
2. ABS lamp: Indicates a fault in the ABS system.
3. ABL "BRAKE" lamp: This lamp is a general brake warning and illuminates two different colors. Red indicates low brake fluid or hand brake engaged. Yellow indicates DSC/ABS fault or system disabled by the switch.

The DSC and yellow ABL lamp are controlled by the MK60 DSC III control unit via the CAN bus. The ABS lamp is controlled directly by the MK60 via hardwire.

Hand Brake Switch

The hand brake switch is an input to the MK60 DSC to cancel MSR regulation.

Principle Of Operation

The scope of control for the MK60 DSC III is comprised of three systems

1. ABS
2. ASC+T
3. DSC

Based on signals coming from the various sensors, the MK60 DSC III will determine which system is best suited to maintain control of the vehicle.

In addition to the three basic systems, there are several sub-functions which are activated during very specific circumstances. The sub-functions are

Scheme 93

1. CBC
2. EBV
3. MSR
4. ADB
5. DBC
6. MBC

System: Anti-Lock Braking System (ABS)

The ABS system can prevent wheel lock when braking by comparing the four active wheel speed sensors to the average vehicle speed. If a wheel is locking during braking or has dropped below a speed threshold programmed in the control unit ABS braking will begin.

ABS braking is possible when vehicle speeds are above 12 kV (7mph).

ABS regulation has three phases

1. Pressure Build
2. Pressure Hold
3. Pressure Release

Pressure Build already occurs during normal braking, so when ABS first intervenes it will start holding pressure by energizing the Inlet Valve. For example, if the right rear wheel is locking up, both Inlet Valves will be energized, regulating both wheels together. This logic is known as Select Low. Front wheels can be regulated individually as needed to prevent lockup.

Energizing the Inlet Valve closes the brake fluid passage to the calipers and traps the fluid at the current pressure, thus not allowing the brake pressure to rise any further.

If the wheel speed does not increase the Pressure Release phase begins.

Scheme 94

Pressure Release occurs when the control unit energizes the Outlet Valve while continuing to hold the Inlet Valve closed. The trapped brake fluid is released out of the calipers, reducing braking pressure.

At the same time, the pump is switched on which draws in the released brake fluid and pumps it back into the pressure-build circuit restoring the volume of brake fluid again in front of the Inlet valve.

Depending on conditions the ABS system may cycle between these three phases from 3 to 12 times a second to prevent wheel lock.

Corner Brake Control (CBC)

CBC can occur if the vehicle is cornering and ABS regulation is not taking place.

If the control unit detects transverse acceleration in excess of 0.6g and the brakes are applied, CBC prevents a build up in brake pressure to the inside rear wheel. This prevents the vehicle from entering into an unstable situation that can lead to Oversteer.

The MK60 accomplishes this by closing the Inlet Valve, thus not allowing brake pressure to increase at the brake caliper.

The difference in braking force between the two rear wheels creates a yaw force that opposes the oversteer and allows the vehicle to handle neutrally.

Scheme 95

Electronic Brake Force Distribution (EBV)

EBV will adjust brake pressure to the rear axle based on the rate of slow-down of the rear wheels, ensuring even brake force between the front and the rear of the vehicle.

The control unit monitors the wheel speed when the brakes are applied and compares the deceleration of the front and rear axle to determine required regulation.

If the vehicle is moderately to fully loaded, the rear axle will take longer to slow down, rear wheel brakes can then be applied at a higher pressure.

If a vehicle was lightly loaded, a similar brake pressure would be too great and result in an unstable situation.

If EBV control intervention is required, the control unit cycles the inlet valve on the rear brake calipers to prevent further build-up.

Benefits of EBV are

1. Enhanced braking due to even distribution of brake force.
2. Rear wheel brake size can be increased.
3. Front and rear brakes wear at a similar rate.

Automatic Stability Control (ASC+T)

Based on input from the wheel speed sensors, the MK60 control unit determines if the vehicle is loosing traction due to excessive longitudinal (straight line) wheel slip. An ASC regulating sequence is initiated if the wheel slip exceeds the control units stored allowable values.

Scheme 96

Scheme 97

A critical slip ratio of up to 5% between the wheels will cause the traction control regulation to begin. This slip ratio is established when the system detects a wheel spin difference of 2MPH or greater.

ASC regulation is cancelled at any time if the brake pedal is applied.

The MK60 can control longitudinal wheel slip by two means

1. Engine Intervention
2. Brake Intervention (ADB, drive wheels only)

Engine Intervention

Engine torque may be reduced by

1. Reducing the throttle opening angle
2. Retarding the ignition
3. Canceling individual cylinders by fuel injection cutout. The MK60 DSC III control unit determines the amount of torque reduction that is necessary and sends the request for regulation to the DME via the CAN bus.

Brake Intervention (ADB)

Brake intervention is applied to the individual drive wheel which is loosing traction by regulating the brake calipers in three phases

1. Pressure Build
2. Pressure Hold
3. Pressure Release

When brake intervention is necessary, the front wheels must be isolated from the Pressure Build sequence in the hydraulic unit.

Here is an example of an ASC brake intervention at the left rear wheel

1. The Changeover Valve for the rear brake circuit, the right rear and both front Inlet Valves are energized and closed.
2. The rear brake circuit Intake Valve is energized and opened.
3. The Return/Pressure pump is activated and draws brake fluid through the open Intake Valve from the Master Cylinder (via the Central Valve) and delivers the pressurized fluid to the open Inlet Valve braking the left rear wheel.
4. Pressure Hold and Pressure Release are done by cycling the Inlet and Outlet Valves similar to the ABS sequence described previously.

The control unit decides which regulation method should take place based on input criteria and chooses from two regulating principles

1. Select-High
2. Select-Low

Select-High Regulation

In a Select-High regulation, the MK60 control unit selects the drive wheel with the highest amount of traction and uses it as the basis for evaluation.

1. Engine torque is reduced slightly by request to the DME.
2. The wheel with the least amount of traction is braked. This allows a torque transfer to the wheel with the higher amount of traction (similar to a locking differential). Select-High is used if the vehicle speed is below 40 kV (25 mph).

Select-Low Regulation

In a Select-Low regulation, the MK60 control unit selects the drive wheel with the lowest amount of traction and uses it as the basis for evaluation.

1. Engine torque is reduced until the wheel slip is no longer present.
2. Brake regulation is not carried out.

Select-Low is used if the vehicle speed is above 40 kV (25 mph).

Engine Drag Torque Reduction (MSR)

If the vehicle is driven in low gear when coasting down hill, or if there is a sudden shift to a lower gear, the wheels may be slowed by the engine's braking effect too rapidly. This could result in an unstable situation.

If the front wheels are turning faster than the rear wheels, the MK 60 control unit signals the DME via the CAN bus to raise the engine torque. DME cancels fuel cut-off and allows the engine speed to increase, this allows the drive wheels to accelerate to match the speed of the non-driven wheels.

MSR regulation is cancelled if the brake pedal or hand brake are applied.

Modified ADB Function (2-Wheel Drive Vehicles Equipped With MK60)

The ADB is an automatic differential lock that improves traction. The slipping wheel is braked by pressure built up in the hydraulic unit. The drive torque can be transferred to the wheel with the greater traction, which can transmit drive power to the road. This function takes the place of a limited slip differential.

The MK60 DSC III system incorporates two methods of ADB based on the DSC switch input to the control unit. With the system "on" the ADB works with engine intervention at a threshold of below 40kph(24 mph).

Tapping the DSC switch (<2.5 s) increases the slip threshold of the ADB up to approximately 70 kV (42 mph) for the purpose of increasing traction.

This feature is also helpful for example when rocking a vehicle out of mud or snow.

Scheme 98

Dynamic Stability Control (DSC)

With the introduction of DSC systems, lateral dynamics were taken into account for the first time. The MK60 DSC III system will initiate a DSC regulation sequence if the control unit detects a difference between the drivers desired turning angle and the actual rotation angle of the vehicle. The control unit determines vehicle stability based on

1. Steering wheel angle
2. Wheel speed
3. Transverse acceleration forces
4. Rotation angle and speed (yaw)

Once the control unit determines that the vehicle is in an unstable situation, it also identifies whether it is oversteering or understeering. This distinction is important because it determines which control strategy should be used to help stabilize the vehicle.

DSC regulation consist of

Scheme 99

1. Engine intervention
2. Engine and brake intervention (any wheel)
3. Brake intervention

Understeer

Understeer occurs when the driver wishes to turn a corner but despite the front wheels being turned in the direction of the curve the vehicle continues its track forward. This occurs when the front wheels no longer have sufficient lateral locating force (traction).

The MK60 DSC III can identify the situation and initiate a corrective action based on engine torque reduction followed by a controlled brake intervention sequence if needed.

Engine torque reduction is carried out by the DME from a request by the DSC via the CAN bus. The DME telegrams the torque reduction confirmation back to the DSC.

Brake intervention is carried out by the MK60 hydraulic unit if the driver is not actively braking. An example of a brake intervention at the inside rear wheel is as follows

Scheme 100

1. All Inlet Valves are closed except for the right rear inlet.
2. Intake Valve for rear circuit is opened.
3. Both Changeover Valves are closed.
4. Return pump operated.

Just as an ASC regulation, DSC brake intervention carries out

Scheme 101

1. Pressure Build
2. Pressure Hold
3. Pressure release

Oversteer

Oversteer occurs when the driver wishes to turn a corner and the tail of the vehicle slides outward leading the turn. This is caused by the rear tires loosing traction and not being able to hold against the centrifugal force acting upon the vehicle.

The MK60 DSC III can identify the situation and initiate a corrective action based on engine torque reduction followed by a controlled brake intervention sequence if needed.

Engine torque reduction is carried out by the DME from a request by the DSC via the CAN bus. The DME sends the torque reduction confirmation back to the DSC.

Scheme 102

Brake intervention is carried out by the MK60 hydraulic unit if the driver is not actively braking. An example of a brake intervention at the left outside wheel is as follows

Scheme 103

1. All Inlet Valves are closed except for the left rear inlet.
2. Intake Valve for rear circuit is opened.
3. Both Changeover Valves are closed.
4. Return pump operated.

Dynamic Brake System (DBS)

DBS is designed to assist the driver in emergency braking situations by automatically increasing pressure to the vehicles brake system. This allows the vehicle to stop in the shortest distance possible. DBS was first available in 1999 Bosch DSC III 5.7 systems. It is available on a Continental Teves system for the first time with MK60 DSC III.

The DBS system contains two functions: Dynamic Brake Control and Maximum Brake Control. DBS functions are programmed into the MK60 control unit and require no additional hardware over conventional DSC.

Dynamic Brake Control (DBC)

The DBC function is designed to provide an increase in braking pressure up to the ABS threshold during rapid (emergency) braking situations. The MK60 control unit monitors the inputs from the brake light switch and the brake pressure sensors on the master cylinder.

The triggering criteria for activation of DBC is, how rapidly is the brake pressure increasing with an application of the brake pedal. The triggering conditions are

1. Brake light switch on.
2. Brake pressure in the master cylinder above threshold.
3. Brake pressure build-up speed above threshold.
4. Vehicle road speed above 3mph (5kmh).
5. Pressure sensor self test completed and sensors not faulted.
6. Vehicle traveling forward.
7. Not all of the wheels in ABS regulation range.

If the threshold for DBC triggering is achieved, the MK60 control unit will activate a pressure build-up intervention by activating the return pump. The pressure at all wheels is increased up to the ABS regulation point. This ensures that the maximum brake force is applied to the vehicle.

During DBC the rear axle is controlled with Select-Low logic and the front wheels are regulated individually. DBC will continue until

1. The driver releases the brake pedal.
2. Brake pressure falls below threshold.
3. Vehicle road speed below 3mph. DBC will also be switched off if a fault occurs in with any of the necessary input sensors. A fault in DBC will illuminate the "BRAKE" (ABL) lamp yellow to warn the driver, depending on the type of failure the DSC lamp may be illuminated as well.

Maximum Brake Control (MBC)

The MBC function is designed to support driver initiated braking by building up pressure in the rear brake circuit when the front wheels are already in ABS regulation.

The additional braking pressure is applied to bring the rear wheels up to the ABS regulation point shortening the stopping distance. The MBC function is triggered when the brakes are applied more slowly than the threshold needed for a DBC regulation. The triggering conditions are

1. Both front wheels in ABS regulation.
2. Vehicle road speed above 3mph (5kmh).
3. DBC and pressure sensor initialization test successful.
4. Vehicle traveling forward.
5. Rear wheels not in ABS regulation.

If the threshold for MBC triggering is achieved, the MK60 control unit will activate a pressure build-up intervention by activating the return pump. The pressure at the rear wheels is increased up to the ABS regulation point. This ensures that the maximum brake force is applied to the vehicle.

The MBC function will be switched off if

1. Front wheels drop out of ABS regulation.
2. The driver releases the brake pedal.
3. Brake pressure falls below threshold.
4. Vehicle road speed below 3mph.

MBC will also be switched off if a fault occurs in with any of the necessary input sensors.

A fault in MBC will illuminate the "BRAKE" (ABL) lamp yellow to warn the driver, depending on the type of failure the DSC lamp may be illuminated as well.

Diagnosis of the MK60 DSC III is carried out using the DISplus or MoDiC

Scheme 104

Coding

Coding must be performed after replacement of the MK60 control module or the steering angle sensor. ZCS coding is found in the Coding and Programming selection from the start screen or when pressing the Change button. Follow on-screen instructions for initialization of components after completing the coding process.

Scheme 105

Adjustment Functions

Adjustment (initialization) is required when

1. Replacing the MK60 Control Unit.
2. Replacing/Re-coding the Steering Angle Sensor.
3. Replacing one or both Brake Pressure Sensors.
4. Replacing Lateral Acceleration Sensor.

The steering angle sensor requires an offset adjustment after the sensor has been replaced, coded or after repairs to the steering or suspension system. The offset adjustment informs the steering angle sensor processor of the straight ahead position of the front wheels.

The adjustment is performed by completing the Test Module found in Service Functions.

Once the adjustment is complete the sensor sends an identification number over the CAN bus to the DSC control unit. The ID provides confirmation that the steering angle sensor is coded and has successfully completed the adjustment procedure.

Special Tools

Special Tools available for the Teves DSC III MK60 consist of

Scheme 106

Scheme 107

BOSCH DSC III 5.7

Model: E46/16

Production Date: 330xi 6/00, 325xi 9/00

The Bosch DSC III 5.7 is used in the E46/16 in place of the DSC III MK 60 used on 2wd vehicles. The DSC system is the same as used in the E53. HDC is not a feature on 2001 Xi models.

Functions that are specific for the All-Wheel Drive system are

1. Modified ABS function.
2. ASC+T (All-Wheel Drive version).
3. Four wheel ADB function.

The Bosch DSC III 5.7 system is designed to maintain the vehicles stability during

1. ABS braking regulation
2. ASC+T traction control
3. DSC for oversteer and understeer control

Additional features are also programmed into the control module to enhance driver safety and comfort. These features are

1. CBC Corner Brake Control
2. EBV Electronic Brake Proportioning
3. MSR Engine Drag Torque Reduction
4. DBS Dynamic Brake System

Scheme 108

The Bosch DSC III 5.7 for the E46/16 consists of the following components

1. Integrated Control Unit/Hydraulic Unit with CAN Interface
2. Tandem Brake Master Cylinder
3. Brake Fluid Expansion Tank with Integrated Level Sensor
4. Pre-Charge Pump
5. Brake Pressure Sensor (Located on Hydraulic Unit)
6. Brake Light Switch
7. 4 Wheel Speed Sensors (Active)
8. Rotation Rate/Transverse Acceleration Integrated Sensor
9. Steering Angle Sensor
10. DSC Button
11. Instrument Cluster Warning Indicators
12. Handbrake Switch
13. Wiring Harness

The Bosch DSC III 5.7 control unit/hydraulic unit is located inside the engine compartment on the right hand side.

Both the control unit and the hydraulic unit are replaceable as separate components.

All processing functions for ABS, ASC and DSC are performed in the combined control/hydraulic unit. The control unit is also responsible for processing the wheel speed signals and providing them to other control units.

Scheme 109

Scheme 110

The hydraulic unit consist of an aluminum block containing 12 solenoid valves, 2 pressure accumulators and the return pump.

1. 4 inlet solenoid valves (N/O)
2. 4 outlet solenoid valves (N/C)
3. 2 intake solenoid valves (N/C)
4. 2 changeover solenoid valves (N/O)

The solenoid valving ensures that normal braking is possible in the event of a defective control unit.

Note. N/O= Normally Open, N/C=Normally Closed

The Bosch DSC III 5.7 is connected to the CAN bus for communication with the AGS, DME control module, Steering Angle Sensor and the Instrument Cluster.

Using the CAN bus, all of the connected modules can receive information or send commands.

Communication with the DSC III 5.7 includes

Scheme 111

1. DME - The DME sends current engine torque. DSC commands the DME to reduce (ASC/DSC) or raise (MSR) engine torque.
2. AGS - The DSC commands the AGS to suppress shifts during regulation.
3. LEW - The DSC receives steering angle information.
4. KOMBI - The DSC commands the instrument cluster to activate or deactivate the warning lamps.
5. All four wheels speed signals are sent over the CAN bus for use by other modules.

Tandem Brake Master Cylinder

The DSC III 5.7 system uses a tandem brake master cylinder fitted with central valves as other DSC master cylinders. The central valves allow fluid to be drawn through the master cylinder during ASC and DSC regulation. The hydraulic circuit is split front/rear.

An orifice for pre-charge pressure is fitted into the brake front axle circuit and is connected to the pre-charge pump via a steel braided flexible line.

Brake Fluid Expansion Tank with Integrated Level Switch

The brake fluid expansion tank has internal baffles that reduce foaming during return pump operation.

The expansion tank includes a pick-up tube for clutch master cylinder fluid supply and a second lower one for the charge pump supply.

The brake fluid level switch is incorporated into the tank. The switch is a reed contact switch. If the brake fluid is at a sufficient level, the switch is closed and switched to ground.

Scheme 112

If the fluid level drops below a specified level, the reed contacts open and the DSC responds by switching off the ASC/DSC functions.

Normal braking and ABS operation is unaffected.

The pre-charge pump is located below the master cylinder in the left side of the engine compartment.

During ASC or DSC regulation with brake intervention, the DSC control unit activates the pre-charge pump. The pump delivers brake fluid at a pressure of 10 to 15 Bar to the front axle circuit of the master cylinder. The pressurized fluid also acts on the rear brake circuit of the master cylinder as well.

The Pre-charge pump ensures that an adequate amount of brake fluid is available at the hydraulic unit during brake regulation.

Scheme 113

Brake Pressure Sensor

The brake pressure sensor is mounted on the DSC hydraulic unit in the front axle circuit. The sensor is provided with a 5V reference voltage by the DSC control unit.

The sensor provides the control unit with an analog signal proportional to brake pressure.

Voltage increases with increasing brake pressure.

Scheme 114

Plausibility With Brake Light Switch (BLS)

The signal input from the brake light switch is compared with the pressure sensor value.

The pressure sensor must not detect more that 5 bar when the BLS is not actuated.

Both signals are used to form a redundant BLS input which is monitored during all phases

The brake switch is an input to the DSC to inform it that the brakes are being applied. If the signal is received during an ASC control, brake regulation is interrupted.

Scheme 115

The E46/16 uses Hall-effect wheel speed sensors similar to other models with Bosch DSC III 5.7. The advantages of the Hall sensors over the inductive sensors of the Teves MK 20EI are

1. Speed signal is available from 0.3km/h.
2. Signal strength is not dependent on road speed.
3. The signal supplied is a digital square wave.

The pulse wheel for the front axle circuit is integrated into the wheel bearing inner seal, identical to that of E38, E39, E53, E52 models.

The pulse wheel for the rear axle circuit is identical to 2wd E46 models. The pulse wheel is a plastic coated metal wheel attached to the rear stub axle outboard C.V. Both pulse wheels produce 48 pulses:1 wheel revolution.

The color of the sensor connector is blue, just as the Magnetoresistive sensors of the Teves MK 60 used on 2wd vehicles. The front sensors of the 2wd and 4wd versions of E46 are physically different and will not fit in the wheel hub.

The rear sensors can be confused with the Teves MK 60 sensors and will fit in the rear axle of the 4wd car however they are not compatible with the Bosch system.

Scheme 116

Principle Of Operation Of The Active Wheel Speed Sensor

The sensor housing contains the evaluation circuitry, a Hall-effect transmitter and a permanent magnet. The wheel speed sensor receives a stabilized 8V operating power supply from the control unit.

Both front and rear sensors are two-wire. One wire is for the power supply, the other provides a ground for the Hall element and also provides the input signal to the control module If a tooth of the pulse wheel is opposite the sensor, the signal to the DSC III is high: approx.

1.9 to 3.9 V. When opposite of the gap, the signal to the DSC III is low at 0.35 to 1.3 V.

Integrated Rotation Rate and Transverse Acceleration Sensor

The E46/16 uses the combined rotation rate/transverse acceleration sensor used in all Bosch DSC III 5.7 systems. The sensor is located under the drivers seat in front of the left seat rail and is attached to a plate with a rubber mounting to isolate it from vibrations.

For rotational speed, the sensor produces a reference signal of 2.5 volts and a voltage input signal from 0.7 to 4.3 volts. This signal represents the rotational movement (yaw) of the vehicle from the neutral straight ahead position.

Scheme 117

The sensor also integrates the transverse acceleration signal (side-ways acceleration). The signal range is 0.5V increasing to 4.5V as side forces (g-force) increase. This signal is combined with the rotation signal to determine when to start DSC regulation.

Scheme 118

Note. Adjustment of sensors is conducted separately in Service Functions of the Diagnosis Program even though both sensors are contained in one housing.

The Steering Angle Sensor is mounted towards the lower end of the steering column, above the flexible coupling. The LEW consists of a potentiometer and a built in microprocessor. The potentiometer has two pickups offset at 900 to one another. The raw potentiometer signal is processed and converted into a digital signal that is transmitted over the CAN bus to the DSC control unit.

Scheme 119

The sensor requires initialization in-order to create a zero point default. Once initialized, the LEW sends an ID number to the DSC control unit. The ID provides confirmation that the LEW is properly initialized.

The total steering wheel angle is determined by combining the CAN telegram signal, the stored zero point default and the actual number of turns to the wheel. In order to prevent the LEW from loosing count, KL 30 is provided to the sensor and it continues to record even after the ignition has been switched off.

The DSC calculates the drivers desired rate of turn from the steering angle signal.

Scheme 120

Note. Refer to the Workshop Hints for instructions on coding and initializing the sensor.

The DSC button is located on the SZM however the SZM provides no processing, it is simply a housing for the button which is a hardwired input to the DSC control unit.

The function of the button is different than for 2wd vehicles. Brake intervention remains active for the ADB function after pressing the button to turn off the DSC.

Only ASC engine intervention and DSC yaw intervention are deactivated.

The DSC warning lamp will be illuminated to remind the driver that these functions have been disabled. Pressing the button again returns the system to normal status.

Scheme 121

Three warning indicator lamps are arranged in the instrument cluster

1. DSC lamp: Indicates fault in DSC or system disabled by the switch.
2. ABS lamp: Indicates a fault in the ABS system.
3. ABL "BRAKE" lamp: This lamp is a general brake warning and illuminates two different colors. Red indicates low brake fluid or hand brake engaged. Yellow indicates DSC/ABS fault.

The DSC and yellow ABL lamps are controlled by the DSC control unit via the CAN bus.

The ABS lamp is controlled directly by the DSC III 5.7 control unit via hard wire.

The scope of control for the DSC III 5.7 is comprised of three systems

1. ABS
2. ASC+T
3. DSC

Based on signals coming from the various sensors the DSC III will determine which system is best suited to maintain control of the vehicle.

In addition to the three basic systems, there are several sub-functions which are activated during very specific circumstances. The sub-functions are

Scheme 122

1. CBC
2. EBV
3. MSR
4. ADB
5. DBC
6. MBC

The ABS system can prevent wheel lock when braking by comparing the four active wheel speed sensors to the average vehicle speed. If a wheel is locking during braking or has dropped below a speed threshold programmed in the control unit ABS, braking will begin.

ABS braking is possible when vehicle speeds are above 12 km/h (7mph).

The function of ABS for All-Wheel Drive use has an additional variation. During braking on loose surfaces the wedge effect is helpful. Gravel or dirt will build up in front of the tire when the wheel is locked, creating an increased braking effect. The system allows the locking of one or both front wheels up to approx. 20km/h (12mph). This "poor road surface logic" does not affect steerability. As soon as the control unit detects steering wheel change, the ABS system regulates normally again.

ABS regulation has three phases

1. Pressure Build
2. Pressure Hold
3. Pressure Release

Pressure Build already occurs during normal braking, so when ABS first intervenes it will start holding pressure by energizing the Inlet Valve. For example, if the right rear wheel is locking up, both Inlet Valves will be energized, regulating both wheels together. This logic is known as Select Low. Front wheels can be regulated individually as needed to prevent lockup.

Energizing the Inlet Valve closes the brake fluid passage to the calipers and traps the fluid at the current pressure, thus not allowing the brake pressure to rise any further.

If the wheel speed does not increase, the Pressure Release phase begins.

Scheme 123

Pressure Release occurs when the control unit energizes the Outlet Valve while continuing to hold the Inlet Valve closed. The trapped brake fluid is released out of the calipers reducing braking pressure.

At the same time the pump is switched on which draws in the released brake fluid and pumps it back into the pressure build-up circuit restoring the volume of brake fluid again in front of the Inlet valve.

Depending on conditions the ABS system may cycle between these three phases from 3 to 12 times a second to prevent wheel lock.

CBC can occur if the vehicle is cornering and ABS regulation is not taking place.

If the control unit detects transverse acceleration in excess of 0.6g and the brakes are applied, CBC prevents a build up in brake pressure to the inside rear wheel. This prevents the vehicle from entering into an unstable situation that can lead to Oversteer.

The DSC III accomplishes this by closing the Inlet Valve, thus not allowing brake pressure to increase at the brake caliper.

The difference in braking force between the two rear wheels creates a yaw force that opposes the oversteer and allows the vehicle to handle neutrally.

Scheme 124

EBV will adjust brake pressure to the rear axle based on the rate of slow-down of the rear wheels, ensuring even brake force between the front and the rear of the vehicle.

The control unit monitors the wheel speed when the brakes are applied and compares the deceleration of the front and rear axle to determine required regulation.

If the vehicle is moderately to fully loaded the rear axle will take longer to slow down, rear wheel brakes can then be applied at a higher pressure.

If a vehicle was lightly loaded, a similar brake pressure would be too great and result in an unstable situation.

If EBV control intervention is required, the control unit cycles the inlet valve on the rear brake calipers to prevent further build-up.

Benefits of EBV are

1. Enhanced braking due to even distribution of brake force.
2. Rear wheel brake size can be increased.
3. Front and rear brakes wear at a similar rate.

ASC prevents unintentional wheel slip of the drive wheels in every situation.

The DSC III control unit determines if the vehicle is loosing traction due to excessive longitudinal wheel slip based on input from the wheel speed sensors. An ASC regulating sequence is initiated if the wheel slip exceeds the control units stored allowable values.

The DSC III can control longitudinal wheel slip by two means

1. Automatic Stability Control ASC. Engine Intervention
2. Automatic Differential Brake ADB. Brake intervention

ASC Engine Intervention

Engine torque may be reduced by

1. Reducing the throttle opening angle
2. Retarding the ignition
3. Canceling individual cylinders by fuel injection cutout.

The DSC III control unit determines the amount of torque reduction that is necessary and sends the request for regulation to the DME via the CAN bus.

ADB Brake Intervention

The ADB is an automatic differential lock that improves traction. The slipping wheel is braked by pressure built up in the hydraulic unit. The drive torque can be transferred to the wheel with the greater traction, which can transmit drive power to the road. This function acts much like a limited slip differential.

Brake intervention is applied to the individual wheel which is loosing traction by regulating the brake calipers in three phases

1. Pressure Build
2. Pressure Hold
3. Pressure Release

When brake intervention is necessary, the axle not being regulated must be isolated from the Pressure Build sequence in the hydraulic unit. This is accomplished by closing both Inlet Solenoid Valves for that axle.

Here is an example of an ADB brake intervention at the left rear wheel

1. The Changeover Valve for the rear brake circuit, the right rear and both front Inlet Valves are energized and closed.
2. The rear brake circuit Intake Valve is energized and opened.
3. The Return/Pressure pump is activated and draws brake fluid through the open Intake Valve from the Master Cylinder (via the Central Valve) and delivers the pressurized fluid to the open Inlet Valve braking the left rear wheel.
4. Pressure Hold and Pressure Release are done by cycling the Inlet and Outlet Valves similar to the ABS sequence described previously.

The drive torque can be distributed to the wheels with high friction coefficients (traction).

Scheme 125

Longitudinal Differential-Lock Function

By performing brake intervention at the axle with a low friction coefficient, drive torque can be transmitted to the front wheels.

Scheme 126

Longitudinal And Transversal Differential-Lock Function

By performing brake intervention at the diagonally opposing wheels with a low friction coefficient, drive torque can be transmitted to the two wheels with more traction.

Scheme 127

If the vehicle is driven in low gear when coasting down hill, or if there is a sudden shift to a lower gear, the wheels may be slowed down by the engine braking effect to rapidly. This could result in an unstable situation.

If the front wheels are turning faster than the rear wheels the DSC III control unit signals the DME via the CAN bus to raise the engine torque. DME cancels fuel cut-off and allows the engine speed to increase, this allows the drive wheels to accelerate to match the speed of the non-driven wheels.

MSR regulation is cancelled if the brake pedal or hand brake is applied.

With the introduction of DSC systems, lateral dynamics were taken into account for the first time. The DSC III system will initiate a DSC regulation sequence if the control unit detects a difference between the drivers desired turning angle and the actual rotation angle of the vehicle. The control unit determines vehicle stability based on

1. Steering wheel angle
2. Wheel speed
3. Transverse acceleration forces
4. Rotation angle and speed (yaw)

Once the control unit determines that the vehicle is in an unstable situation, it also identifies whether it is oversteering or understeering. This distinction is important because it determines which control strategy should be used to help stabalize the vehicle.

DSC regulation consist of

1. Engine intervention
2. Engine and brake intervention (any wheel)
3. Brake intervention

Understeer occurs when the driver wishes to turn a corner, but despite the front wheels being turned in the direction of the curve, the vehicle continues its forward track. This occurs when the front wheels no longer have sufficient lateral locating force (traction).

The DSC III can identify the situation and initiate a corrective action based on engine torque reduction followed by a controlled brake intervention sequence if needed.

Engine torque reduction is carried out by the DME from a request by the DSC via the CAN bus. The DME sends the torque reduction confirmation back to the DSC.

Brake intervention is carried out by the DSC III hydraulic unit if the driver is not actively braking. An example of a brake intervention at the inside rear wheel is as follows

Scheme 128

1. All Inlet Valves are closed except for the right rear inlet.
2. Intake Valve for rear circuit is opened.
3. Both Changeover Valves are closed.
4. Return pump operated.

Just as an ASC regulation, DSC brake intervention carries out

Scheme 129

1. Pressure Build
2. Pressure Hold
3. Pressure release

Oversteer occurs when the driver wishes to turn a corner and the tail of the vehicle slides outward, leading the turn. This is caused by the rear tires loosing traction and not being able to hold against the centrifugal force acting upon the vehicle.

The DSC III can identify the situation and initiate a corrective action based on engine torque reduction followed by a controlled brake intervention sequence if needed.

Engine torque reduction is carried out by the DME from a request by the DSC via the CAN bus. The DME sends the torque reduction confirmation back to the DSC.

Scheme 130

DBS is designed to assist the driver in emergency braking situations by automatically increasing pressure to the vehicles brake system. This allows the vehicle to stop in the shortest distance possible. DBS was first available in 1999 Bosch DSC III 5.7 systems.

The DBS system contains two functions: Dynamic Brake Control and Maximum Brake Control. DBS functions are programmed into the DSC III control unit and require no additional hardware over conventional DSC.

The DBC function is designed to provide an increase in braking pressure up to the ABS threshold during rapid (emergency) braking situations. The DSC III control unit monitors the inputs from the brake light switch and the brake pressure sensor. The triggering criteria for activation of DBC is, how rapidly is the brake pressure increasing with an application of the brake pedal. The triggering conditions are

1. Brake light switch on.
2. Brake pressure in the master cylinder above threshold.
3. Brake pressure build-up speed above threshold.
4. Vehicle road speed above 3mph (5km/h).
5. Pressure sensor self test completed and sensor not faulted.
6. Vehicle traveling forward.
7. Not all of the wheels in ABS regulation range.

If the threshold for DBC triggering is achieved, the DSC III control unit will activate a pressure build-up intervention by activating the pre-charge and return pump. The pressure at all wheels is increased up to the ABS regulation point. This ensures that the maximum brake force is applied to the vehicle.

During DBC the rear axle is controlled with Select-Low logic and the front wheels are regulated individually. DBC will continue until

1. The driver releases the brake pedal.
2. Brake pressure falls below threshold.
3. Vehicle road speed below 3mph.

DBC will also be switched off if a fault occurs in with any of the necessary input sensors.

A fault in DBC will illuminate the "BRAKE" (ABL) lamp yellow to warn the driver, depending on the failure the DSC lamp may be illuminated as well.

The MBC function is designed to support driver initiated braking by building up pressure in the rear brake circuit when the front wheels are already in ABS regulation.

The additional braking pressure is designed to bring the rear wheels up to the ABS regulation point shortening the stopping distance. The MBC function is triggered when the brakes are applied more slowly than the threshold needed for a DBC regulation. The triggering conditions are

1. Both front wheels in ABS regulation.
2. Vehicle road speed above 3mph (5km/h).
3. DBC and pressure sensor initialization test successful.
4. Vehicle traveling forward.
5. Rear wheels not in ABS regulation.

If the threshold for MBC triggering is achieved, the DSC III control unit will activate a pressure build-up intervention by activating the return pump. The pressure at the rear wheels is increased up to the ABS regulation point. This ensures that the maximum brake force is applied to the vehicle.

The MBC function will be switched off if

1. Front wheels drop out of ABS regulation.
2. The driver releases the brake pedal.
3. Brake pressure falls below threshold.
4. Vehicle road speed below 3mph.

MBC will also be switched off if a fault occurs in with any of the necessary input sensors.

A fault in MBC will illuminate the "BRAKE" (ABL) lamp yellow to warn the driver, depending on the failure the DSC lamp may be illuminated as well.

Workshop Hints

Diagnosis of the DSC III 5.7 is carried out using the DISplus or MoDiC. The diagnosis program utilizes the symptom driven diagnostics taken from the E53.

The all-wheel drive models of the E46 series do not have their own model identification and all-wheel drive specific equipment (i.e. DSC III 5.7) is not detected automatically. All-wheel drive identification is performed by manually selecting it from a pop-up dialog box when a document or test module is called up which has a variation for all-wheel drive.

Diagnosis: Faults with the DSC III 5.7 system can be diagnosed using symptom driven test modules. To begin diagnosis

1. Perform the Quick Test.
2. Page right.
3. Press the Function Selection Button.
4. Select Complete Vehicle.
5. Select Chassis.
6. Select "Yes" for All-Wheel.
7. Select Dynamic Stability Control.
8. Press the Test Schedule Button.

Diagnosis can occur using Fault Symptoms or Expert Mode troubleshooting.

Service Functions: Provides access to specialized functions used in post repair procedures. To enter

Scheme 131

1. Select Service Functions while in Diagnosis Program. The Contents are
2. Test Code: Used to print control unit fault information needed for component analysis.
3. Adjust Steering-Angle Sensor: Used to adjust off-set for steering angle sensor when repairs or adjustments to steering have been made.
4. Adjust Transversal Acceleration Sensor/Adjust Rotation Rate Sensor: Used to adjust offset for each sensor.
5. Bleeding,ABS/DSCHydraulics/Precharging-pump circuit: Used in purging air after repairs and for brake fluid flushes.
6. ABS/DSC Final Test: Used to verify the proper brake pipe connections to the hydraulic unit and wheel speed sensor connections.

Coding must be performed after replacement of the DSC III control module or the steering angle sensor. ZCS coding is found in the Coding and Programming selection from the start screen or when pressing the Change button. Follow on-screen instructions for initialization of components after completing the coding process.

Scheme 132

Adjustment (initialization) of certain components is required when

1. Replacing the DSC III Control Unit.
2. Replacing/Re-coding the Steering Angle Sensor.
3. Replacing Rotation/Lateral Acceleration Sensor.

The steering angle sensor requires an offset adjustment after the sensor has been replaced, coded or after repairs to the steering or suspension system. The offset adjustment informs the steering angle sensor processor of the straight ahead position of the front wheels.

The adjustment is performed by completing the Test Module found in Service Functions.

Once the adjustment is complete, the sensor sends an identification number over the CAN bus to the DSC control unit. The ID provides confirmation that the steering angle sensor is coded and has successfully completed the adjustment procedure.

Special Tools available for the Bosch DSC III 5.7 consist of

Scheme 133

Scheme 134

Traction and Stability Control Systems Application Chart

TRACTION AND STABILITY CONTROL SYSTEMS APPLICATION REFERENCE

S = STANDARD EQUIPMENT

O = OPTIONAL EQUIPMENT