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The function light signals that the air conditioning system is in standby mode.

The compressor only cuts in if the switch-on conditions are fulfillled. The evaporator

then produces cold air which is raised to the required temperature in reheat mode

with the aid of the heat exchanger.

Activation of A/C compressor relay

The A/C compressor relay is activated by the engine control unit. The activation

request is sent by the air conditioning control unit via CAN.

Full load cutout

In order to shorten the rev-up time of the engine from idle up to full load, the

electromagnetic clutch is switched off for a limited period of time at full throttle. The

cutout time is between 4 and 10 s depending on the type of engine.

Full load condition: Speed signal < 14 km/h and acceleration

Idle increase (anti-stall)

The air conditioning control unit sends the AC and KO signals via the CAN bus to

ensure engine operating refinement is not impaired by the compressor load.

When switching on the air conditioning system, the AC signal requests an increase

in the idle speed from the engine control unit. When the signal is active, the engine

control unit increases the idle speed irrespective of the magnetic clutch.

Compressor activation

With the KO signal, the A/C control unit informs the engine control unit of its intention

to switch on the compressor. Consequently, the DME implements an interfering

variable circuit, i.e. it moves the throttle or the idle speed control valve in the

direction "more air" while at the same time increasing the injection volume.

On the E36 and E46 The A/C compressor relay is then activated by the engine

control unit. Only relay activation is monitored by the diagnosis function of the

engine control unit but not the compressor itself.

On the E38 and E39 the engine control unit sends a reply in the form of the

DME_KOREL signal (compressor relay) to the A/C control unit to switch on the A/C

compressor. If all conditions for switching on the A/C compressor are fulfillled, the

A/C compressor is activated directly by the control unit.

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Fully sequential fuel injection

In the fully sequential fuel injection system, each fuel injector is activated by its own

output stage.

Fully sequential fuel injection offers the following advantages:

- Improved mixture preparation for each individual cylinder

- Adaptation of the injection timing to the relevant engine operating status (engine

speed, load, temperature)

- Cylinder-selective injection correction under changing engine load conditions, i.e.

during one operating cycle can vary the injection timing by means of post-injection,

extending or shortening injection

- Cylinder-selective cutout is possible (e.g. in the event of defective cylinder coil)

- Diagnosis of each individual fuel injector is possible

These advantages of fully sequential fuel injection are gained because all cylinders

are independently supplied with fuel.

Activation of each individual fuel injector by means of a separate output stage

ensures that the presupply of the fuel is the same for all cylinders thus ensuring

uniform mixture preparation quality for all cylinders. The presupply time is variable

and is dependent on the engine load, speed and temperature.

In view of the fact that fuel injection only takes place once for each revolution of the

camshaft the scatter of the fuel supply rate is low due to the component tolerances.

Added to this, the idle quality is also improved as the energization and

deengerization times at the fuel injectors are reduced. Fuel consumption is also

slightly lower.

The injection timing can be corrected while driving as the result of sudden

acceleration or deceleration. If the fuel injectors are still open, the mixture can be

corrected at the valves that not have not yet injected fuel, are currently injecting fuel

or have already injected fuel by means of short post-injection or correspondingly

lengthening or shortening the injection timing. This achieves improved response

characteristics of the engine.

Another important improvement is that in the event of one output stage failing, the

engine can still continue operation on the remaining cylinders to the nearest BMW

service workshop.

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Fuel injection during engine start has been improved in order to achieve more

effective starting characteristics.

During engine start, a quantity of fuel is pre-injected at an engine speed > 20 rpm.

This quantity is dependent on the engine coolant temperature. This ensures fuel is

applied to the intake duct and inlet valves.

Renewed pre-injection after turning off the engine only takes place if the engine was

running for at least 20 seconds.

MS42 only

The fuel injectors are designed as two-hole fuel injectors.

This type of fuel injector is necessary because of the web arranged between both

intake valves. The same quantity of fuel is injected at both fuel injectors in order to

achieve improved mixture preparation. This requirement is ensured by the new

design of the fuel injectors.

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relay and delivers the fuel via the fuel filter to the fuel distributor pipe.

Fuel pump relay

The control unit can only monitor activation of the relay but not of the pump itself. A

safety circuit ensures the relay can only be activated with the engine running and

only shortly after switching the ignition lock to position 2 in order to build up

pressure.

Once the engine shuts down, the DME control unit no longer recognized engine

speed and immediately switches off the relay. This ensures that the fuel pump

cannot continue running when the engine turned off.

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washer water, underfloor protection or engine fumes.

Procedure

A small and a large fuel circuit serve the purpose of preventing fuel overheating. The

large fuel circuit is required during the starting phase in order to flush the fuel

injection rail with the complete delivered quantity of fuel. Power is applied to the 3/2-

way valve (fuel circuit changeover valve) for this purpose. The 3/2-way valve is thendeactivated, i.e. power is no longer applied, and the small fuel circuit assumes fuel

supply As a result, the surplus fuel delivered by the fuel pump now only flows

through the small fuel circuit and is returned to the fuel tank via the return line. Only

the amount of fuel that is used by the engine is now delivered up to the injection rail.

In this way, the quantity of fuel in the small circuit which is located outside the engine

compartment is heated up to a far lesser extent so that fuel evaporation is also

reduced.

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vehicle functions from the steering wheel. These functions include:

- Radio functions

- Telephone functions

- Cruise control functions

In addition to a high degree of comfort, the multifunction steering wheel also offers

the driver increased safety as it is not necessary to take the hands off the steering

wheel to operate various functions. The driver can implement the functions from the

multifunction steering wheel without diverting his attention from the traffic situation.

The response times to multifunction steering wheel operations are so fast that there

is no noticeable delay in the feedback.

For cruise control purposes, on the MS42, the signals for the cruise control function

are sent from the multifunction steering wheel to the engine control unit where they

are evaluated. There is no separate cruise control unit.

Cruise control (Tempomat) operation

A keypad for cruise control operation is located on the right-hand side of the steering

wheel. Description of operating keys from top to bottom:

- Resume : The vehicle accelerates or decelerates from non-controlled operation to

the driving speed last set and maintains this speed.

- Accelerate : The speed is increased by 1 km/h by briefly hitting this button. If

pressed longer, the speed is increased until the button is released again. Cruise

control is only switched on, however, if all switch-on conditions are fulfillled. These

switch-on conditions are:

- "Accelerate" button in neutral position before switching on cruise control.

- Minimum speed of 30 km/h must be exceeded.

- The brake pedal must be in rest position.

- The clutch pedal must be in rest position on vehicles with manual transmission.

- Drive stage "2" to "D" must be engaged on vehicles with automatic transmission.

- No switch-off condition must be active. Switch-off conditions are possible either by

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or they can arise as the result of detected fault statuses. The corresponding fault

codes are stored in the fault code memory.

- Decelerate : The driving speed is reduced from the set cruise control by pressing

the "decelerate" button on the steering wheel. The speed is decreased by 1 km/h

by briefly hitting this button. If pressed longer, the speed is decreased until the

button is released again. However, it is not possible for the driving speed to drop

below the minimum set speed.

The deceleration function is terminated by a switch-off condition occurring:

- Deactivation via main switch

- Operating brake pedal

- Operating clutch pedal (manual transmission)

- Engaging drive stages "P" or "N" (automatic transmission)

- OFF : Switching off cruise control (Tempomat) function. After switching the ignition

lock to position 1 or 2, cruise control assumes standby mode by operating the

main switch (I/0). Standby mode is a system preparation function (arming) that

must be carried out before switching on the cruise control. It is intended to prevent

the cruise control being switched on by unintentional operation of one of the

controls. Tempomat standby is indicated by an LED in the instrument cluster.

Following standby and after fulfillling all switch-on conditions, cruise control can be

activated by pressing the "acceleration" button.

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- S_BLS (brake light switch)

- S_BLTS (brake light test switch)

The DME control unit evaluates the signals for the purpose of registering brake

operation.

Function

The brake light switch switches to ground (B-), the brake light test switch to B+. The

plausibility of both signals is checked.

The following table shows how the signals behave:

Brake light switch is Brake light test switch is

Brake pedal operated open closed

Brake pedal not operated closed open

Troubleshooting

A fault code is stored if the signals are not plausible. Cruise control is deactivated as

a result.

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It has its own voltage supply.

If the brake light switch is OK, it assumes a high-resistance setting when the ignition

is switched off, i.e. it sends a signal as if it were operated. If this is not the case, this

indicates a short to ground and the messages "brake light defective" as well as "rear

right lamp defective" and "rear left lamp defective" are output or indicated in the

pictogram in the instrument cluster.

The light switching center recognizes the "operated" status if there is a break in the

line. If is recognizes the switch interrupted for longer than 10 s as operated, the light

switching center then also makes use of the vehicle acceleration signal. If a conflict

is then detected, the above-specified error messages are output.

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on vehicles with manual transmission.

Function

The clutch switch switches to ground. The plausibility of the signal is checked

together with cruise control.

The following table shows how the signal behaves:

Clutch switch is

Clutch operated open

Clutch not operated closed

Troubleshooting

A fault code is stored if the signal is not plausible. Cruise control is deactivated as a

result.

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Mixture Preparation

An engine should operate satisfactorily under all operating conditions and ensure the

energy it receives is utilized to a maximum. The fuel-air mixture must be optimally

prepared for this purpose. Only in this way can effective combustion take place and

provide the corresponding engine power output. Added to this, effective combustion

also ensures that pollutant emissions are kept within acceptable limits.

Adaptation makes it possible for the engine control unit to learn certain values fromcomponents and equipment variants thus making it possible to compensate for

certain component tolerances. A fault is indicated if adaptation exceeds certain

limits.

Lambda adaptation

Lambda adaptation serves the purpose of compensating for component tolerances

that influence the mixture and aging effects.

Factors such as secondary air and fuel pressure also have an effect on lambda

adaptation and are, in part, also compensated.

For this reason, exact intervention limits in the case of fault cannot be specified.

Lambda adaptation differentiates between idle (additive) and partial load

(multiplicative) mixture adaptation:

- Idle adaptation is effective at idle speed and in the range close to idle speed. Itsinfluence decreases as the engine speed increases (an important factor is

secondary air for instance).

- Partial load adaptation is effective over the entire characteristic map range (an

important factor is the fuel pressure for instance)

Fuel-air mixture

A gasoline engine requires a certain air-fuel ratio (lambda) in order to operate

effectively. The theoretical air-fuel ratio is 14.7 : 1.

Different operating conditions (cold, warm, acceleration, etc.), however, render

necessary an air-fuel mixture that deviates from the ideal value. Mixture correction

must take place with the aid of various facilities.

A rich mixture is necessary during full throttle operation in order to develop the

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There is insufficient air if lambda is < 1. The fuel-air mixture is rich. The engine

develops its maximum power output at lambda = 0.85 to 0.95.

There is surplus air if lambda is > 1. The air-fuel mixture is lean. As a result, fuel

consumption and power output are reduced.

If lambda is > 1.3, the air-fuel mixture no longer readily ignites, the engine no longer

runs, the operating limit is exceeded.

A lambda value of 0.9 to 1.1 has proven to be the most favorable in practical

applications. If, however, it is necessary to operate the engine about a lambda value

= 1, a fuel injection with emission (lambda) control will be necessary for the purpose

of mixture preparation.

The electronic fuel injection system measures the air drawn in by the engine and

converts the measured value into an electrical signal that is evaluated by the DME

control unit. The control unit calculates the fuel requirement on the basis of the

electronic signal and other parameters. The control unit correspondingly activates

electromagnetic fuel injectors. These fuel injectors intermittently inject fuel ahead of

the inlet valves of the cylinders.

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troubleshooting purposes.

The engine must run at idle speed for at least 3 minutes to ensure that the correct

values are set. Smooth idle speed can only be evaluated with the engine running at

idle speed (cold or hot). An indication of the combustion quality of individual

cylinders can be obtained by evaluating the crankshaft acceleration, measured at

the crankshaft position/rpm sensor. An individual cylinder with poor combustion can

be detected very well in this way.

Random fluctuations of the individual cylinders can only be detected by close

observation of the value. The values over all cylinders are zero in the engine with

theoretically uniform combustion.

An increase in the smooth-running values may be caused by various factors (e.g.

misfiring, secondary air, mixture deviations, faults in fuel supply, low compression).

For this reason, exact intervention limits cannot be specified.

The rotational speed (engine speed) of the engine is measured at the incremental

wheel with the aid of a hall-effect sensor. Moreover, the smooth running of the

engine is also monitored (misfire detection) as a measure of the engine speed.

To detect misfiring, the increment gear is divided (by the control unit) into 3

segments corresponding to the ignition interval, i.e. 3 sparks per crankshaft turn on a

6-cylinder engine and 2 sparks in 2 segments on the 4-cylinder engine. Within the

control unit, the periodic duration of the individual increment gear segments is

measured and statistically evaluated. For each point on the characteristic map, the

maximum permissible rough running values are stored as a function of engine

speed, load and engine temperature.

If these values are exceeded within a certain number of combustion cycles, the

cylinders detected as faulty are stored in the fault code memory.

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Operation of an engine with knocking combustion over a prolonged period can lead

to serious damage. Knocking tendency is increased by:

- Increased compression ratio

- High cylinder charge

- Poor fuel quality (RON/MON)

- High intake air and engine temperatures

The compression ratio can also reach excessively high values due to deposits or

production-related scatter.

On engines without knock control, these unfavorable influences must be taken into

consideration in the ignition design by providing a safety distance to the knock limit.

However, this results in unavoidable losses in efficiency in the upper load range.

The knock control can prevent knocking engine operation. For this purpose, it

retards the ignition timing of the cylinder(s) concerned (cylinder-selective) as far as

necessary only when there is an actual danger of engine knocking. In this way the

ignition characteristic map can be laid out to combustion-optimum values without

having to take the knock limit into consideration. A safety distance is no longer

necessary.

The knock control system carries out all knock-related corrections to the ignition

timing and enables perfect operation also with regular grade fuel (minimum RON

91).

The knock control provides:

- Protection against knocking damage also under unfavorable conditions

- High efficiency due to optimum utilization of the fuel quality and consideration of

the relevant engine status

- Logistics advantages with regard to fuel availability

- Lower consumption and higher torque over the entire upper load range

(corresponding to the fuel quality used).

Design of knock control system

The M52 and M43 are equipped with a cylinder bank-selective, adaptive knock

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signals are evaluated in the DME control unit.

The knock sensor is a piezo-electric structure-borne noise microphone. It picks up

the structure-borne noise and converts it into voltage signals.

Function of the knock control system

If knocking occurs, the ignition is retarded for a certain number of working cycles

and then gradually approaches the original value. The retard setting can be

controlled individually for each cylinder bank (cylinder bank selective).

In the event of the knock sensor failing, a fault code is entered in the fault code

memory of the DME control unit. In the case of fault, the engine is protected by

constant retard setting of the ignition timing.

Installation Locations/Conditions

The double knock sensor is secured by means of an 8 mm screw on the water jacket

of the engine block between both cylinder banks. It is arranged such that each

sensor monitors one cylinder bank.

Only screw locking compound may be used to lock the screws. Washers, spring

washers or serrated lock washers must under no circumstances be used.

Self-diagnosis and emergency operation of the knock control system

Self-diagnosis of the knock control system includes following checks:

- Check for sensor signal interference/line break, plug connector defective etc.

- Self-test of entire evaluation circuit

- Check of basic engine noise level detected by the knock sensor

The knock control system is switched off if a fault is found during the course of one

of these checks. The emergency program adopts the task of controlling the ignition

timing. At the same time, a defect code is stored in the defect code memory. The

emergency program ensures damage-free operation as from minimum RON 91. It

depends on the engine load, speed and temperature.

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endeavours to provide the ideal air-fuel mixture ratio (Lambda = 1) for combustion.

Stereo lambda control is used on the M52 with MS42. The oxygen sensors are

mounted in the exhaust manifold.

There is only one bank on the M43 with BMS46. The oxygen sensors are mounted

in the Y-pipe.

They measure the residual oxygen in the exhaust gas and send corresponding

voltage values to the control unit. Here, if necessary, the mixture composition is

corrected accordingly in that the injection timing is varied. In the event of the oxygen

sensor failing, the engine control unit assumes emission control with a programd

substitute value (approx. 0.45 V). This location allows the dead times for the

individual exhaust paths to be reduced and more precisely monitored.

On the M52, each oxygen sensor registers three cylinders with corresponding

exhaust section (cylinders 1-3 and 4-6). Test example: If the injector opening time of

the first line of cylinders (cylinders 1-3) is changed, a reaction should be observed

on the oxygen sensor of the first line. If this is not the case, renew the probes.

On the M43, one oxygen sensor senses all 4 cylinders.

The operation of the control oxygen sensor is similarly monitored. Malfunctions of

the oxygen sensor, e.g. caused by using leaded fuel, are detected in the engine

control unit by a change in the lambda control frequency.

The oxygen sensors are heated as a temperature of approx. 300C is required for

effective operation of the oxygen sensors. The heater is actuated by the engine

control unit.

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monitoring the efficiency of the catalytic converter and monitoring the function of the

oxygen sensors before the catalytic converter.

The oxygen sensors are heated as a temperature of approx. 300 C is required for

effective operation of the oxygen sensors. The heater is actuated by the engine

control unit.

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independent of the accelerator pedal position.

The motor-driven throttle valve in the M52 and MS42 differs from electronic engine

management (EML) in following points:

- No potentiometer on accelerator pedal but rather a double potentiometer on the

pulley of the motor-driven throttle valve

- There is a bowden cable fitted between the accelerator pedal and motor-driven

throttle valve which is also used for emergency operation purposes.

Deleting adaptations on completion of repair (M52):

The adaptations should generally not be deleted on completion of repairs (parts

replacement). After replacing the throttle valve (MDK) the adaptation values should

be deleted in order to avoid a fault code entry.

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Function

Periodic pressure fluctuations are produced in the intake pipe by the induction

strokes of the cylinders. These pressure waves run through the intake tube and are

reflected at the closed inlet valves. The intake tube length precisely adapted to the

valve timing ensures that a pressure peak of the reflected air wave reaches the inlet

valve just before the end of its opening range. A post-charging effect is achieved in

this way. This post-charging effect conveys a larger volume of fresh mixture into the

cylinder.

DISA utilizes the advantages of short and long intake pipes.

Short intake pipes or intake pipes with a large diameter have the effect of producing

higher output values in the upper engine speed range together with lower torque

values in the medium engine speed range. Long intake pipes or intake pipes with a

small diameter develop high torque in the medium engine speed range.

Operating principle

A headpipe is arranged ahead of the oscillating tubes of the two cylinder banks.

When the connecting flap valve is closed , the headpipe and oscillating tube

together act as a long intake pipe. The pulsating gas column produces a distinct

increase in torque in the medium engine speed range.

The connecting flap between the two cylinder banks is opened in order to

increase the output in the upper engine speed range. As a result, the dynamics of

the headpipes is reduced to a large extent. The short oscillating tubes which are now

effective enable higher output values in the upper engine speed range.

The vacuum tank is evacuated by the vacuum applied in the intake pipe in the partial

load range. The connecting flap is closed with the aid of the vacuum unit and the

pneumatic actuator.

If the switching speed is exceeded, the DME control unit deactivates the solenoid

valve, i.e. it is switched off. As a result, the vacuum unit is aerated and the flap

opened.

As soon as the solenoid valve switches (on dropping below the switching speed) the

vacuum reservoir and vacuum unit are reconnected and the connecting flap closed.

The switching speeds for activation and deactivation are shifted with respect to each

other (hysteresis) in order to avoid opening and closing in rapid succession.

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the event of a fault in the electropneumatic flap operation. This ensures the complete

engine output is available in the upper engine speed range (e.g. for overtaking). The

basic setting of the flap is therefore "open".

The flap is returned or opened by means of two springs:

- A torsion spring on the flap shaft

- A coil spring in the diaphragm cell

The solenoid valve is activated directly via a powerful output stage in the DME

control unit.

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actuator. The rotary slide valve in the idle speed control valve may only be tested by

way of activation via a tester or by shaking. It is not permitted to move the rotary

slide valve with the finger or with the aid of a tool such as a screwdriver. This would

mean that the rotary slide valve would no longer function correctly.

The idle speed control valve is now responsible for several tasks and is therefore an

important component in the intake air tract of the engine.

Small air leaks which may occur, for example, at leaking gaiters/cylinders or in the

event of a varying gap in the throttle valve can be compensated up to a certain

extent by the idle speed control valve.

The idle speed control valve opens a little more during the engine coasting phase

and closes just before reaching idle speed. This prevents a high intake pipe vacuum

and blue smoke emission (oil vapor via valve stem seals).

During engine start, the idle speed control valve enables an opening cross section

that is above that of idle speed. This ensures the engine starts more efficiently.

The idle speed control valve features an emergency operation opening gap which

ensures certain limp-home functions in the event of power failure.

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A heated surface of the hot-film air mass sensor in the flow of intake air is controlled

to a constant temperature with respect to the intake air. The intake air flowing past

this surface cools this heated surface and thus changes its resistance. The heating

current which is necessary in order to maintain the constant temperature is the

measurement variable for the air mass drawn in. The DME control unit uses it to

calculate the load signal and thus the basic variable for the injection timing.

Important advantages:

- Changes in air pressure (air density) are recorded

- Temperature influences are compensated

- No moving parts

- Large measuring range

- Low pressure drop in the intake pipe due to low air resistance. This improves the

efficiency of the engine.

In contrast to the hot-wire mass air sensor, clear-burning of the sensor is no longer

necessary after the engine has been turned off. Any dirt deposits on the surface do

not influence the sensor signals directly since the protective film cleans itself due to

the constant overtemperature.

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sensor while on the M52 it is screwed into the intake plenum. A precision NTC

resistor is used to convert the "temperature" into a measurement value "resistance"

which can be evaluated electrically by the DME control unit.

The intake air temperature sensor is not required for correction of the injection timing

as the intake air temperature is automatically taken into consideration in the air mass

measuring procedure. The intake air temperature sensor is required for the start

procedure in conjunction with the engine coolant temperature sensor. The resistance

values of both sensors supply exact information for calculating the injection timing.

In this way hot start problems in particular are avoided.

The air column in the mass air flow sensor can oscillate during the start procedure.

For this reason, the value output by the mass air flow sensor cannot be used as a

correct value for injection timing.

During the start procedure, the temperature sensors are therefore used as a

measurement variable up to a freely programmable engine speed threshold.

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engine control unit. The crankshaft position/rpm sensor is designed as a Hall-effect

sensor. An incremental wheel indicates the current crankshaft position. The

crankshaft position/rpm sensor sends out a square-wave signal as the engine turns

over.

Steps taken by engine control unit in the event of a fault in the crankshaft

position/rpm sensor.

If the crankshaft position/rpm sensor is faulty, a corresponding fault code "crankshaft

position/rpm sensor" is stored in the fault code memory of the engine control unit.

The camshaft sensor signal is then used as the engine speed signal (emergency

operation).

Possible effect: Misfiring is possible and start characteristics deteriate.

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The housing is made of die cast aluminum or plastic and is screw-mounted on the

timing case cover. The dual temperature sensor for the coolant is installed in the

water pump housing. This dual temperature sensor is located at the point where the

coolant flows out of the engine.

Detail view water pump with dual temperature

sensor

Radiator

An engine oil cooler is additionally fitted for specific country variants.

Function of a conventional thermostat

The control of the engine cooling system with a conventional thermostat is

determined by the coolant temperature only. This control system can be subdivided

into three operating ranges:

- Thermostat closed: The coolant only flows in the engine. The radiator circuit is

closed.

- Thermostat open: The entire volume of coolant flows via the radiator. This ensures

the maximum cooling capacity available is utilized.

- Thermostat control range: A part of the coolant volume flows via the radiator. The

thermostat sets a constant engine inlet temperature within the control range.

With the aid of the characteristic map thermostat, the coolant temperature can now

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In this way it is possible to set a higher coolant temperature in the partial load range

of the engine. Higher operating temperatures in the partial load range achieve

improved combustion, reflected in lower fuel consumption and pollutant emission.

However, higher operating temperatures in the full load range would involve specific

disadvantages (ignition timing (angle) reduction due to knocking). For this reason,

lower coolant temperatures are set specifically in the full load range with the aid of

the characteristic map thermostat.

Control characteristics of characteristic map cooling

1 Characteristic curve of a 110 o C thermostat

2 Characteristic curve of a characteristic map thermostat

3 Characteristic curve of an 85 o C thermostat

4 Partial load range

5 Full load range

6 Partial load range

With the aid of this thermostat it is possible to specifically increase the coolant

temperature in the partial load range. By increasing the coolant temperature under

these engine operating conditions, it is possible to reduce fuel consumption. This

characteristic map thermostat is controlled by the engine control unit dependent on a

characteristic map.

This characteristic map is determined by the following factors:

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- Engine speed

- Vehicle speed

- Intake temperature

- Coolant temperature

Design of the characteristic map thermostat

The characteristic map thermostat is an integral thermostat, i.e. the thermostat and

thermostat cover make up one unit.

The principle mechanical design of the characteristic map thermostat corresponds to

that of a conventional thermostat. However, a heating element is additionally

integrated in the expansion element (wax element).

Cross sectional view of the characteristic map

thermostat

The cover of the characteristic map thermostat is made of an aluminum die casting.

The electrical connection for the heating element linked to the expansion element of

the characteristic map thermostat is integrated in the thermostat cover.

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Characteristic map thermostat with electrical

connection for heating element

Function of the characteristic map thermostat

The characteristic map thermostat is designed such that it opens (engine inlet) at a

coolant temperature at the thermostat of 103 oC without intervention of the

integrated heating system. Due to the coolant heating up in the engine, a

temperature of approx. 110 oC is measured at the point the coolant flows out of the

engine (installation location of coolant temperature sensor for DME and instrument

cluster gauge). This is the operating temperature of the engine, at which the

characteristic map thermostat begins to open without control intervention.

In the event of control intervention by the DME control unit, power (12 V) is applied

to the heating element integrated in the thermostat. Heating the expansion element

means that the thermostat now opens at lower coolant temperatures than would be

the case without the additional heating function (thermostat control range: approx.

80 oC - 103 oC).

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1 Opening path of the thermostat

2 Coolant temperature

3 Activation of heating element with 12 V

4 Activation of heating element with 0 V

If the coolant temperature exceeds 113 oC at the engine outlet, the heating of the

characteristic map thermostat is activated by the DME irrespective of the other

parameters.

Diagnosis

The line connection and the function of the characteristic map thermostat are

monitored by the diagnosis function in the DME control unit. Any faults are stored in

the fault code memory of the DME control unit.

Coolant temperature gauge

The indicator characteristics of the coolant temperature gauge in the instrument

cluster have been adapted to the higher temperature level of the engine due to the

use of the characteristic map thermostat.

The pointer of the coolant temperature gauge in the instrument cluster is located in

the mid-position at coolant temperatures of

75 oC - 113 oC

in center position.

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temperature by means of its variable resistor (NTC= Negative Temperature

Coefficient).

Among other things, the coolant temperature serves as a measurement variable for

following functions:

- Start volume calculation

- Injection volume calculation

- Set idle speed

- Characteristic Map Cooling

In the event of the engine coolant temperature sensor failing, a fault code is entered

in the DME control unit and a substitute value is calculated from the value of the

intake air temperature sensor with the aid of a temperature model.

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coolant temperature after it flows out of the radiator.

The coolant temperature at the radiator outlet serves the purpose of driving the

electric fan.

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accurate indication of the engine temperature than the engine coolant temperature.

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the equipment. The electric fan cuts in when the cooling capacity of the viscous fan

is no longer sufficient.

The electric fan is activated by means of a power output stage directly on the fan

motor. The motor control unit activates this power output stage by means of a

square-wave signal with duty factors (variable pulse width) between 10 and 90 %

thus controlling the various speeds of the electric fan. Pulse duty factors less than 5

% and greater than 95 % do not trigger activation but rather they are used for fault

detection purposes. The power output stage features its own positive and ground

supply.

The fan speed is influenced by the coolant temperature at the radiator outlet and the

pressure in the air conditioning system. The fan speed is reduced as the vehicle

speed increases.

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Hall-effect sensor.

It is necessary for the fully sequential injection system (fuel injection takes place

individually for each cylinder at the specific firing point). In the event of a fault in the

camshaft sensor, emergency phase recognition is implemented on the M43 with

BMS46 with the aid of the misfiring detection function.

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medium engine speed ranges. Reduced valve overlap results in lower residual gas

quantities while idling. Nitrous oxide components are reduced by internal exhaust

gas recirculation in the partial load range. This achieves faster heating of the

catalytic converters, lower untreated emissions after cold start and reduced fuel

consumption.

VANOS inlet/exhaust

A controlled VANOS unit is installed on the M52 with MS42 for inlet and exhaust. It

is activated by means of an electromagnetically operated 4/3-way valve.

The required position of the inlet and exhaust camshafts is calculated from the

engine speed and load signal depending on the intake air and engine temperature

and the VANOS unit is controlled accordingly by the engine control unit. The inlet

and exhaust camshafts can be variably controlled within their maximum adjustment

range, i.e. any arbitrary positions are possible corresponding to the specified values

of the engine control unit. When the relevant optimum camshaft position is reached,

the solenoid valves maintain a constant oil volume in the adjustment cylinder on both

sides of the chamber so that the camshafts remain in the corresponding positions.

When the engine starts up, the inlet camshaft is in its end position, i.e. it is initially in

the retard position. During engine start, the exhaust camshaft is held in the advance

position by means of a spring.

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the brake booster. When no power is applied, the suction jet pump valve is open and

has a brake pressure boosting effect. Depending on the engine temperature and

selector lever position, power is applied to the valve of the suction jet pump when

the vacuum is at sufficient levels even without the suction jet pump.

The suction jet pump valve is installed on the M52 with the MS42 only in the E46 up

to 4/98 and on the M43 with BMS46 only in vehicles with automatic transmission.

The suction jet pump is constantly effective in all other models.

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Positive and ground supply

The engine control unit features a permanent positive and ground supply.

Diagnostic link

The engine control unit can be addressed via the tester with the diagnostic link.

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for several functions.

- It serves the purpose of maintaining the programd top speed. Once this is

achieved, the mixture and ignition are varied and individual ignition and injection

signals masked out as required thus ensuring smooth shut-down.

- On vehicles with the air conditioning switched on compressor activation is

interrupted up to a driving speed of 13 km/h when accelerating under full load.

- Idle speed control is activated at a driving speed signal > 0 km/h, i.e. the idle speed

has a fixed value that is normally just above the engine speed when the vehicle is

stationary.

- The idle speed is controlled accordingly if the driving speed is 0 km/h. However, it

is still corrected by the A/C signal, drive stage information on automatic vehicles

and the light switch input.

- Poor road surfaces are also detected by means of the speed signal. The smooth-

running monitoring function is deactivated if a poor road surface is detected.

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A transponder chip is integrated in each of the vehicle keys. A ring coil is fitted about

the ignition lock. The transponder chip is powered by the EWS3 control unit via this

coil, i.e. no battery is required in the key. The power supply and data transfer take

place in the same way as a transformer between the loop antenna (coil) at the

ignition lock and the transponder chip.

The key then sends data to the EWS3 control unit. If these data are correct, the

EWS 3 control unit enables the starter by means of a relay located in the control unit

and additionally sends a coded start enable signal via a data link to the DME/DDE.

These procedures may result in a start delay of up to half a second.

Components

Data link to DME/DDE

The EWS3 control unit sends a coded enable signal to the DME/DDE via the data

link. The engine cannot be started before this signal has been transferred.

Engine control unit (DME/DDE) with coded start enable input

The engine control unit (DME/DDE) only enables engine start if a correct enable

signal is received from the EWS control unit.

EWS-DME/DDE interface

Identical variable codes are stored in the EWS 3.3 control unit and in the DME/DDE

control unit. The value of these codes changes after every start procedure. Start

enable only takes place if the code sent by the EWS control unit agrees with the

code calculated in the DME/DDE control unit.

The control units are allocated only during initial programming of the DME/DDE

control unit. The engine control unit then adopts the basic code of the EWS control

unit.

Important!

It is not possible to replace the DME/DDE or EW 3.3 control units for test

purposes !

In rare cases, it is possible that the variable codes in both control units deviate from

each other. In these cases, it is possible to reset both codes to the initial value via

the service function DME(DDE) EWS III matching.

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Key identification and start procedure

The following procedure takes place after inserting the vehicle key in the ignition

lock:

- The transponder in the key is powered via the loop antenna and sends the key

data to the EWS3 control unit.

- The EWS3 control unit then checks the key data to ensure it is correct and only

then sends an enable signal to the engine management system and starter.

- After the engine has started, the EWS3 control unit generates new key data

(change code) and transfers them to the transponder in the key.

- A new variable code is also created and stored in the DME/DDE control unit.

Fault recognition in engine control unit

The following faults are monitored in the engine control unit:

- Interface, i.e. line to EWS control unit: In this case, the check is carried out in order

to establish whether a signal is received and whether this signal is not subject to

excessive interference.

- Variable code: A check is conducted as to whether the variable code which is sent

by the EWS control unit agrees with the value calculated in the DME(DDE) control

unit.

Engine start is inhibited if a fault is detected.

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connected stations are equally entitled, i.e. each control unit can both send as well

as receive. In other words, the connected control units can "communicate" and

exchange information via the lines.

Due to the linear structure of the network, the bus system is fully available for all

other stations in the event of one station failing. The connection consists of two data

links (CAN-L and CAN-H) which are interface-protected by means of shielding

(CAN-S).

Data exchange between the following control units takes place via the CAN bus:

- DME control unit

- Instrument cluster

- ASC/DSC control unit

- Transmission control unit

The connected control units must all have the same CAN status. The CAN status

can be checked via the diagnosis interface. The CAN status (bus index) is specified

on the identification of the relevant control unit connected to the CAN-bus.

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Secondary air system monitor

Automatic monitoring is carried out to ensure that the secondary air system is

functioning correctly. For this purpose, operation of the secondary air injection and of

the shut-off and air switch-over valves is monitored each time they are activated.

The secondary air injection serves as an exhaust gas aftertreatment during the

engine warm-up phase. For this purpose, fresh air is injected directly into the

exhaust manifold to ensure the catalytic converter heats up at a faster rate.

Shortly after the engine is started, the secondary air pump is activated by the SLP

relay. The time until it is switched on is dependent on the following fringe conditions:

- Engine temperature

- Load signal

- Engine speed

Monitoring principle

The oxygen sensor voltage is monitored in the engine control unit during activation

of the secondary air pump. During problem-free operation of the secondary air

system, the oxygen sensor voltage is primarily in the lean range.

At regular intervals (every 20 ms), the oxygen sensor voltage is registered within the

control unit. Each measurement in which the oxygen sensor voltage is registered as

being in the lean range is counted by an internal counter. If this count exceeds a

predefined threshold, the system is recognized as being fully operational. If this

threshold is not reached the engine control unit assumes there is a fault in the

secondary air system. An entry is made in the fault code memory.

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13 - Activation, VANOS solenoid valve, outlet

15 - Activation, VANOS solenoid valve, inlet

1B - Activation, idle speed actuator/closing coil

35 - Activation, idle speed actuator/opening coil

44 - Activation, solenoid valve, fuel tank ventilation

6E - Signal, drivers choice sensor, potentiometer 1

70 - Signal, throttle position sensor, potentiometer 1

73 - Reference voltage, voltage regulator 1

AA - Control unit self-test, internal fault

AB - Plausibility, motor-driven throttle valve

the control unit should on no account be replaced.

These fault codes are entered in the above list if the system voltage was too low due

to battery discharge or due to failure or contact fault of the DME main relay.

DME main relay

The relay is driven by the DME control unit.

Function of main relay:

Voltage supply to all components in the engine electrical/electronic system

Possible effects: - Engine does not run

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scavenging air. The scavenging air drawn through the carbon canister is enriched

with hydrocarbons (HC) according to the level of charge of the activated carbon

(HC) and then fed into the engine for combustion.

The development of hydrocarbons from the fuel tank is highly dependent on:

- the fuel and ambient temperatures

- air pressure

- the fuel level within the tank

The tank vent valve is closed when in a flow-free state. This prevents fuel vapors

from the AKF reaching the intake manifold when the engine is not running.

On-board diagnosis II

Regardless of the pollutants created by the combustion within the engine, a vehicle

will emit considerable amounts of unburned hydrocarbons. These hydrocarbon

emissions can stem from leaks in the fuel system, but also from an insufficiently

large fuel tank vent system (carbon canister becomes permeable).

For this reason, a further OBD II requirement concerns the fuel system and the fuel

tank ventilation system. The maximum permissible level of escaping fuel fumes has

been determined anew. Moreover, leaks larger than 1 mm in the fuel system must

be recognized by the DME.

To this end, the following measures have been implemented in BMW vehicles:

- Fuel temperature reduction by fuel circuit with 3/2-way valve

- The carbon canister has been reshaped

- New activated carbons with improved absorption capability

- Inclusion of a fuel tank ventilation system diagnosis function in the engine control

unit with the aid of a carbon canister shut-off valve and fuel tank pressure sensor

Fuel tank vent system diagnosis

Fuel tank vent system diagnosis is performed automatically in predefined cycles. It

is only performed with the engine running. The entire system must be closed off air-

tight in order to be able to determine leaks in the fuel tank and fuel tank ventilation

system. This is achieved by the shut-off valve (AAV) on the carbon canister (AKF).

Vacuum system:

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mbar in the entire system has been generated by the intake system. The vacuum in

the fuel tank system is measured by the fuel tank pressure sensor.

The fuel tank vent valve is closed when the required vacuum is attained.

Now, the fuel tank vent valve and the carbon canister shut-off valve are both closed

together. In this state, the DME control unit uses the fuel tank pressure sensor to

monitor the previously generated vacuum in the fuel tank and fuel tank vent system.

The engine control unit assumes that there is a leak if the vacuum is reduced by

more than a defined threshold within a period of approx. 10 seconds.

Overpressure system:

The LDP (leak detection pump) is switched on and the fuel tank ventilation valve

closed. The LDP remains on until a pressure of 5-10 mbar in the entire system has

been generated. The pressure in the tank is measured by the reed switch in the

LDP.

The LDP is switched off when the required pressure has been reached.

Now, the fuel tank vent valve and the carbon canister shut-off valve are closed

together, the LDP is switched off. In this state, the DME control unit uses the fuel

tank pressure sensor to monitor the previously generated overpressure in the fuel

tank and fuel tank vent system. The engine control unit assumes that there is a leak

if the overpressure is reduced by more than a defined threshold within a period of

approx. 10 seconds.

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ZSR resistance

The following faults are detected based on the ZSR resistance:

- Short-circuits and open-circuits in the primary ignition circuit

- No ignition sparks in secondary circuit

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transmission. This switch converts the current selector lever position into a code.

This selector lever code is transferred via five lines (L1-L5) to the EGS control unit.

Selector lever position L1 to L5 (0 = open, 1= U-batt)

P L1 =1, L2 = 1, L3 = 1, L4 =0, L5=0

R L1 =0, L2 = 0, L3 = 1, L4 =1, L5=0

N L1 =1, L2 = 1, L3 = 0, L4 =1, L5=0

D L1 =0, L2 = 0, L3 = 0, L4 =1, L5=1

4 (3) L1 =1, L2 = 0, L3 = 1, L4 =1, L5=1

3 (2) L1 =0, L2 = 0, L3 = 1, L4 =0, L5=1

2 (1) L1 =1, L2 = 0, L3 = 0, L4 =0, L5=1

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transmission manually. The gear required by the driver is transmitted via three

switches (to ground) in the manual gate to the EGS control unit: The "manual gate"

switch is closed if the selector lever is moved out of the automatic gate into the

manual gate. By pressing the selector lever forward or back, the "strike-up" or

"strike-down" contact is additionally closed.

Note

After installing a new EGS control unit, the selector lever must be moved once into

the "downshift" or "upshift" position with terminal 15 switched on in order for the

control unit to detect that the Steptronic facility is installed.

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signals:

- Brake (brake light switch or brake light test switch)

- Road speed

- Engine speed

- Time

The selector lever is locked when no brake signal is detected with the engine

running and the vehicle stationary. A time delay function of approx. 0.5 s is used for

operation under winter conditions. The brake light switch is designed as a normally-

opened contact referred to 12 V and the brake light test switch as a normally-open

contact referred to ground. The shift lever is locked by way of a solenoid on the

selector lever switch.

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to ground. The switch must be adjusted such as to enable driving under full load, i.e.

100 % accelerator pedal position and the kick-down shift only takes place when the

accelerator pedal is further depressed.

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driver in critical driving situations in maintaining the stability and steerability of the

vehicle.

ABS/ASC variants

All E46 models are equipped as standard with ABS/ASC. DSC III, known from

E38/39, is available as an optional extra on the 2.8 l model. Systems from ITT

INDUSTRIES (formerly Teves) are used on the E46.

The following systems are installed together with the individual types of engines:

- 4-cylinder (M43) models: ABS/ASC-EZA system (brake and engine intervention

without throttle control)

- 4-cylinder M47 models: ABS/ASC with brake intervention and fuel volume control

- 6-cylinder M52 models: ABS/ASC-EZA system (brake and engine intervention with

throttle control)

Technical features

ASC Mk20 EI:

The difference between the ASC MK20 EI and ASC MK4G is in the way the

hydraulics and control unit have been combined to form one unit.

The hydraulic unit and the control unit can be replaced individually in case of

repair! After replacing the control unit or the complete ABS/ASC unit, the new

control unit must be encoded.

Basically, the ABS and ASC functions have remained the same and correspond to

those of the ABS/ASC MK4G. The 6-cylinder models feature the actuator-controlled

throttle valve (MDK). The actuator-controlled throttle valve combines the throttle andchoke in one component.

New functions

Cornering brake control (CBC:) The cornering brake control stabilizes the vehicle

when the brakes are applied while cornering.

Electronic brake force distribution (EBV): The EBV function registers the

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way, braking of the front and rear wheels can be optimally adapted to relevant load

conditions.

ASC system structure

The hydraulic unit is screwed to the control unit to form one complete unit. The

hydraulic units consists of an aluminum block which accepts the valves and the

return pump. 9 solenoid valves and one hydraulically switched valve are arranged inthe block:

- 4 inlet valves (electric)

- 4 outlet valves (electric)

- 1 changeover valve (electric) with integrated pressure relief valve

- 1 charging valve (hydraulic)

Wheel speed sensors with pulse wheel

The system operates with 4 passive wheel speed sensors. The function and design

are the same as on the E36.

Speed signal outputs: The rear left and right speed signals are registered by the

corresponding speed sensors, processed in the control unit and output again as a

square-wave signal.

The rear left speed signal is used as the driving speed signal in the instrument

cluster.

The rear right wheel speed signal serves as the input signal for other control units,

e.g. AGS.

Brake light switch (BLS)

The brake light switch (active) is necessary in order to detect operation of the brakes

during ASC control and to consequently terminate ASC control.

In ABS mode, the signal from the brake light switch is used as an input variable thus

increasing control comfort.

The passive brake light switch is still used on E36 vehicles. The type of brake light

switch used (active/passive) is coded in the control unit.

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This button serves the purpose of cutting out and cutting in the ASC system. If the

switch is pressed with the engine running, a 12 Volt signal is switched to the control

unit and the system deactivated. The system is reactivated by pressing the ASC

button once again.

If the vehicle is turned off (engine off) with the ASC system deactivated, the system

is reactivated when terminal 15 is reactivated.

Instrument cluster with ABS/ASC/ABL lamps

Three indicator lamps are provided in the instrument cluster for the purpose of

monitoring the various functions:

- ABS lamp

- ASC lamp

- ABL lamp (general brake warning lamp)

ABS lamp

The ABS lamp is activated directly by the control unit via a separate line:

- ABS lamp comes on for approx. 2 seconds at terminal 15 "ON" (lamp check)

- ABS lamp comes on at terminal 15 "ON" and when ABS fault is found

- ABS lamp is off when ABS is OK.

If the ABS system senses a fault, the instrument cluster recognizes this fault status

by means of a high level and activates the ABS lamp. A defective or not connected

control unit is also detected in this way. The ASC lamp is also activated in the case

of an ABS fault.

ASC lamp

The ASC lamp is activated via the CAN bus:

- ASC lamp comes on for approx. 2 seconds at terminal 15 "ON" (lamp check)

- ASC lamp is off when ASC is OK.

- The ASC lamp flashes at 3 Hz when ASC is active.

- ASC lamp comes on at terminal 15 "ON" when the ASC system is not in operation

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ABL lamp

The ABL lamp (general brake warning lamp) monitors three different functions. It

comes on when:

- The handbrake is applied

- The brake fluid level in the reservoir is too low

- CBC or EBV control is not in operation (e.g. defective rear axle control)

CAN-bus

The ASC control unit communicates with the DME and AGS (if installed) control

units as well as the instrument cluster via the CAN bus. The ASC control unit sends

information on activation/deactivation of the ASC and ABL lamps to the instrument

cluster.

The DME informs the ABS/ASC control unit how high the relevant engine torque is.

When control is active, the ABS/ASC control unit indicates to the DME control unit

whether and by how much the torque is to be reduced.

When control is active, the AGS control unit (adaptive transmission control) receives

relevant information from the ABS/ASC control unit. In this way, another gearshift

characteristic can be realized in order to avoid the automatic transmission constantly

shifting up and down.

Operating principle of hydraulic system

All inlet valves and the changeover valve are open when no power is applied. The

outlet valves are closed when no power is applied. The charging valve closes

hydraulically when the brakes are applied, it is otherwise open.

During ABS control, the pump feeds the brake fluid back into the master brake

cylinder while during ASC control with brake intervention it builds up the necessary

brake pressure. The changeover valve and charging valve are allocated to the brake

circuit of the rear axle. The ABS return pump is capable of building up the necessary

brake pressure only in conjunction with these two valves during an ASC control

phase with brake intervention.

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The basic principle of the ASC system Mk 20 El is the same on all models. The

difference is in the type of engine torque control. On the M43 engine, the control is

based on ignition timing adjustment and individual cylinder blank-out. The M52

engine is controlled by means of the throttle control, ignition timing adjustment and

individual cylinder blank-out. On the M47 diesel engine, the torque is controlled by

varying the injection volume.

Engine drag moment control (MSR)

The engine drag moment control function is also integrated in the Mk 20 El. The

MSR intervenes in the case of excessively high wheel slip when the engine is

coasting or when the driver shifts into a lower gear. It controls the engine drag

moment in order to avoid excessive wheel slip of the driven axle.

ABS/ASC control functionThe control unit starts a self-test when terminal 15 is switched on. If no fault is found,

the next check takes place at approx. 20 km/h, in which all solenoid valves and the

ABS/ASC pump are activated. If this test is also OK, the system is ready for

operation.

The control unit detects whether ABS control braking or ASC control is required by

means of the wheel speed sensors.

ABS control cuts in in case of a change in the wheel circumference or if a fixed slip

threshold is exceeded while braking.

ASC control cuts in if the drive wheels assume excessively high positive slip during

an acceleration phase.

ABS-controlled braking takes place on the basis of the well-known control

philosophy: Individual brake pressure control at the front wheels and common

control of the rear axle.

If the ASC control unit detects excessively high slip of the drive wheels, it can

restabilize the drive axle by way of engine and/or brake intervention.

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The ABS/ASC control unit takes into consideration the longitudinal slip in order to

ensure stable driving characteristics when braking and accelerating.

The DSC system also takes into account the effects of transverse dynamics, i.e.

vehicle instabilities which may occur while cornering, and initiates stabilizing actions.

DSC variants

DSC III is available as an optional extra on the E46 with 2.8 l engine.

System overview DSC III

The DSC III in the E46 consists of the following components:

- Hydraulic unit with control unit (combined as with ASC)

- 4 wheel speed sensors with corresponding pulse wheels

- Prebooster pump

- Tandem master brake cylinder

- Steering wheel angle sensor (LWS)

- Yaw rate sensor

- Transverse acceleration sensor

- 2 Brake pressure sensors

- Brake light switch (BLS)

- Brake fluid level switch

- DSC button

- Instrument cluster with ABS/DSC/ABL indicator lamps

- DME with ignition coil and injection valves

- Adaptive transmission control (AGS), optional

- CAN-bus

- Wiring harness

Technical features

In the same way as with the ASC Mk20 EI, the control unit and hydraulics of

the DSC III are combined in one unit. Both components can be replaced

DSC III: FB

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individually in the case of repair.

Control unit

The electronic control unit corresponds to the AASC Mk20EI with regard to its basic

design and functions.

In addition to the ABS/ASC control functions, it undertakes the corresponding DSC

functions. In order to implement DSC control, the control unit additionally evaluates

the following sensor signals:

- Yaw velocity through yaw rate sensor

- Transverse acceleration through transverse acceleration sensor

- Steering wheel angle through steering wheel angle sensor

The two brake pressure sensors and the brake fluid level switch supply further

signals which are used during a control procedure.

The control unit communicates via the CAN bus with the DME with regard to engine

intervention, the AGS, steering wheel angle sensor and the instrument cluster.

The DSC and ABL indicator lamps are also activated via the CAN bus.

DSC III hydraulic unit

Brake intervention can take place on the front or rear axle during a DSC control

phase. For this reason, two additional solenoid valves have been integrated in the

hydraulic unit:

The hydraulic units consists of an aluminum block which accepts 12 solenoid valves

and the ABS return pump.

- 4 inlet solenoid valves

- 4 outlet solenoid valves

- 2 block valves with integrated pressure relief valve

- 2 changeover solenoid valves

The inlet solenoid valves and block solenoid valves are open when no power is

applied.

The outlet solenoid valves and changeover solenoid valves are closed when no

power is applied.

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This logic ensures that the brakes remain fully operable even in the event of a

control unit defect.

The changeover and block solenoid valves located in the front axle brake circuit

enable brake intervention on the front axle during DSC control.

During ABS-controlled braking, the pump feeds the brake fluid back into the master

brake cylinder while during ASC/DSC control with brake intervention it builds up the

necessary brake pressure and conveys the fluid volume back into the master bake

cylinder.

Brake light switch (BLS)

The brake light switch (active) is necessary in order to detect operation of the brakes

during ASC control and to consequently terminate ASC control. During DSC control,together with the pressure sensors it serves to detect superimposed braking initiated

by the driver.

In ABS mode, the signal from the brake light switch is used as an input variable thus

increasing control comfort.

Wheel speed sensors with pulse wheel

The system operates with 4 active wheel speed sensors.

Speed signal outputs: The rear left and right speed signals are registered by the

corresponding speed sensors, processed in the control unit and output again as a

square-wave signal.

The rear left speed signal is used as the driving speed signal in the instrument

cluster.

The rear right wheel speed signal serves as the input signal for other control units,

e.g. AGS.

Brake fluid level switch

The brake fluid level switch monitors the brake fluid in the reservoir. If the level is

OK. the switch is closed (ground).

If the brake fluid level drops below a certain value, the prebooster pump is switched

off in DSC mode.

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DSC button

The ASC/DSC functions can be deactivated or activated with the DSC button.

If the vehicle is turned off (engine off) with the DSC system deactivated, the DSC

system is reactivated when terminal 15 is reactivated.

Steering wheel angle sensor (LWS 5)

The steering wheel angle sensor is fitted at the bottom end of the steering spindle.

The sensor features a 6-pin plug connector with following pin assignments:

- Pin 1: Terminal 30

- Pin 2: Ignition voltage with run-on (terminal 87)

- Pin 3: CAN-high

- Pin 4: CAN-low

- Pin 5: Ground

- Pin 6: Diagnostic link

Measuring principle: The sensor is designed as a potentiometer with two wipers

offset by 90 degrees. The potentiometer signal is evaluated and converted into

digital form (CAN).

The sensor signals provide a steering wheel angle variable which covers the entire

range of steering wheel rotation. The signal is repeated after every 360 degrees.

Voltage jumps are then evaluated thus determining the steering wheel turns.

The total angle is therefore derived from the sensor signal, the stored steering wheel

angle offset and the number of steering wheel turns.

The steering wheel angle sensor is allocated to a particular type of vehicle. Thisensures that incorrect signals are not obtained from a sensor not belonging to the

vehicle, e.g. after replacement.

For this reason, a steering wheel angle offset must always be carried out after

replacing a sensor otherwise the ASC/DSC function will remain deactivated. In order

to reduce the risk of undetected replacement, the steering wheel angle sensor

requests the vehicle identification number from the instrument cluster via the CAN

bus.

The information on the stored steering wheel turns is lost in the event of voltage dips

at terminal 30, e.g. disconnection of vehicle battery or removal of the steering wheel

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angle sensor. To ensure that the customer is not forced to reinitialize the steering

wheel angle sensor, the current steering wheel turn value is determined by way of

static evaluation of the front wheel speed.

Steering wheel angle sensor (LWS) matching

At the end of the assembly line or in the workshop, zero offset is carried out by

means of diagnosis (front wheels in straight ahead position) after replacing the

sensor (or working on the steering column/steering).

During this offset procedure, the mid-position of the steering wheel is permanently

stored in the EEPROM as the start value. The offset serves as the basis for trouble-

free operation of the steering wheel angle sensor.

In addition to the offset, the DSC III logic continuously determines the steering zeroposition while driving.

The LWS information serves the purpose of determining the cornering speed and

the steering characteristics of the driver. The steering wheel angle sensor also

supplies signals to other systems via the CAN bus.

Transverse acceleration sensor

The transverse acceleration sensor is installed in the left-hand A-pillar. The 3-pin

plug connection to the DSC wiring harness has following pin assignments:

- Pin 1: Sensor signal

- Pin 2: Ground

- Pin 3: Sensor supply voltage (5 Volt)

Measuring range and offset values: Analog voltage from 0.5 to 4.5 Volt. The offset

value is 1.8 Volt (vehicle stationary).

Measuring principle: This sensor is designed as a capacitive sensor.

Function in DSC III system: The measured transverse acceleration is used as a

variable for determining the set yaw rate. This yaw rate corresponds to cornering

which is still stable under the given driving conditions on reaching the cornering limit

speed.

Pressure sensors

The two pressure sensors are located in the master brake cylinder. The 3-pin plug

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connector has the following terminals: Ground, signal voltage, supply voltage (5

Volt).

Measuring range and offset: The sensors supply an analog voltage which

corresponds to a measuring range from 0 to 250 bar. The zero point offset takes

place via diagnosis. In addition, the zero point is continuously corrected by DSC.

Measuring principle: Capacitive sensors

Function in DSC III system:

The information is used to detect and implement braking requirements when the

brake is applied during a control procedure.

Rotation rate sensor

The rotation rate signal (yaw velocity) corresponds to the rotational velocity about

the perpendicular axis of the vehicle.

The rotation rate sensor is mounted under the drivers seat. The 3-pin plug

connector has the following terminals: Ground, signal voltage, supply voltage 5 Volt.

Measuring principle: Quartz crystal tuning fork system

Function in DSC III system:

The measured rotational velocity (yaw rate) is compared with driver requirements

(steering wheel angle, driving speed and transverse acceleration information). The

DSC corrects the vehicle rotational velocity as required by specific brake intervention

at the front or rear axle as well as by influencing the engine torque.

These interventions achieve stable vehicle handling within physical limits under all

driving conditions (braking, propulsion, rolling).

Instrument cluster with ABS/DSC/ABL lamps

The following indicator lamps are provided for DSC in the instrument cluster for the

purpose of monitoring the various DSC III functions:

- ABS lamp (ABS fault lamp)

- DSC lamp (DSC fault lamp)

- ABL lamp (general brake warning lamp)

Activation and function indication of the lamps are identical to the ASC. The

difference is in the DSC lamp instead of the ASC lamp (same symbol). The DSC

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The engine torque can be varied with the following interventions:

- Reduction of air mass drawn in

- Ignition timing retarded

- Cylinder blank-out

Brake intervention by DSC III

Example of brake intervention with DSC system while cornering:

Driving in a right-hand bend: The vehicle turns into the bend when oversteered. A

load moment is produced to oppose the yaw moment by specifically building up an

adapted brake force at the left front wheel. As a result, the vehicle drives under

stable conditions.

In order to build up optimum brake pressure at the wheel brake cylinder, the control

takes place in the phases pressure build-up, pressure retension, pressure reduction.

Whether a wheel on the front or rear axle is to be braked depends on whether the

vehicle is understeered or oversteered.

Excessive understeering is avoided by braking the rear wheel on the inside of the

curve. In this example, this would be the right-hand rear wheel.

Depending on the vehicle status, the wheel of the other axle on the same side may

also be braked slightly.

Description of DSC III control

The DSC III control unit monitors the vehicle stability on the basis of sensor signals.

If the vehicle reaches its dynamic driving limits, the control unit decides whether ABS

control, ASC control or DSC control with or without brake intervention at the front

and/or rear axle is to take place.

Stabilizing intervention is implemented if the control unit determines vehicle

instability from the variables steering wheel angle, wheel speed, transverse

acceleration and yaw rate.

DSC control intervention may be in the form of:

- Engine intervention or

- Engine intervention with brake intervention or

- Brake intervention

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During DSC control, intervention in the engine management only takes place if the

vehicle is understeered. In this situation, the 4 inlet solenoid valves and 2 block

solenoid valves are opened when no power is applied. The 4 outlet solenoid valves

and 2 changeover solenoid valves are closed when no power is applied. Normal

braking is therefore possible.

Pressure build-up by way of example of driving in a right-hand bend and front left

wheel:

As already mentioned, during DSC control, the pressure is always built up with the

assistance of the prebooster pump. The only exception is when braking is

superimposed by the driver.

The following components are activated electrically during front left pressure build-

up:

- Prebooster pump

- Front right inlet valve, rear right inlet valve (rear left inlet valve closed)

- Block solenoid valve of front axle brake circuit closed

- Changeover solenoid valve of front axle brake circuit open

- ABS return pump

In addition to the system components activated during pressure build-up, the front

left inlet solenoid valve must be additionally closed during the pressure retension

phase. The changeover valve is closed.

Pressure build-up:

The front left outlet solenoid valve is activated during this phase. The thus enclosed

brake fluid can escape into the low pressure accumulator and is then conveyed by

the return pump. During renewed pressure build-up this volume of brake fluid can

therefore be fed into one of the wheel brake cylinders or otherwise into the master

brake cylinder.