SKODA Self Study Program 28 – Octavia Electronic Stability Programme (ESP) SSP-28-Octavia-ESP

ESP is the acronym for: "Electronic Stability Programme".

The system is designed to assist the driver in dealing with difficult and unexpected situations, such as when a wild animal crosses the road in front. It is designed to compensate for over-reactions and to help avoiding unstable vehicle states. At the same time, though, ESP is not able to outsmart the applicable laws of Nature.

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The driver's first duty is, and continues to be, to adopt a responsible style of driving which matches road conditions and the traffic situation.

What we wish to present to you in this Self Study Programme is how ESP is based on the tried-and-tested antilock brake system ABS with its related systems of TCS, EDL, EBD and EBC, the physical laws which apply in this case, and how the system operates.

Contents

Introduction 4

Physical Principles 7

Vehicle Dynamic Control 9

System Overview 12

Design and Operation 16

Control loop Control unit Steering angle sensor Lateral acceleration sensor Yaw rate sensor Longitudinal acceleration sensor TCS/ESP pushbutton Brake pressure sensor Active brake servo unit with brake master cylinder Brake light suppression relay Hydraulic unit

Function Plan 36

Self-Diagnosis 38

Service 40

Test Your Knowledge 41

ESP Glossary 42

You will find notes on inspection and maintenance, setting and repair instructions in the Workshop Manual.

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Introduction

A look back

The technical advances in automotive engineering have resulted in ever more powerful and higher-performance vehicles being available on the market. This confronted designers, at a very early stage, with the question of how this technology can remain controllable for the "normal driver".

In other words: Which systems are best able to ensure optimal braking and assistance for the driver?

That is why, even as long ago as the 20s and 40s there were the first mechanical developments of ABS systems. They were not up to the task, however, because of their inert reactions.

It was the mid-60s when automobile designers worldwide began the development of automatic wheel lock systems, and electronic signal processing became a reality with the aid of new semiconductor elements.

This gave rise to the first ABS systems, which have progressively become more powerful and more efficient since then with the advances in digital technology. The first Škoda vehicle fitted with ABS was the Felicia. Today,

it is not only ABS, but also the associated systems of EDL, EBD, TCS and EBC, which are already considered as normal features of a modern car.

The outcome of this development through to production maturity, is the ESP, although the ideas of the engineers already go far beyond this.

What can ESP achieve?

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Advantages:

The Electronic Stability Programme is one of the active safety features of a modern car. We also talk in this connection of a "vehicle dynamic system". To put it in a greatly simplified way, it is an "anti-skid programme". It detects the risk of the vehicle skidding and specifically compensates for the risk of the vehicle breaking away.

– It is not a stand-alone system, but is based

on the other traction systems, in other words it also embraces their performance

features. – It relieves the strain on the driver. – The driver maintains control over the

vehicle. – The risk of an accident resulting from an

over-reaction on the part of the driver, is

reduced.

The acronyms of the vehicle dynamic systems

Here is a brief explanation of the system acronyms and the function of the individual systems.

ABS

ntilock Brake System It prevents the wheels from locking during a brake application. Even at full braking power, directional stability and steerability are maintained.

TCS

raction Control System It prevents the driven wheels from slipping, for example on ice or gravel, by controlling the brakes and the engine management system.

ESP

lectronic Stability Programme It prevents the vehicle from skidding by specifically controlling the brakes and the engine management system (term used by Audi, VW, Ford, Mercedes).

Other manufacturers use the following abbreviations for their systems:

– –

AHS DSC

Active Handling System (Chevrolet) Dynamic Stability Control (BMW)

–

PSM

Porsche Stability Management

(Porsche) – –

VDC VSC

Vehicle Dynamics Control (Subaru)

Vehicle Stability Control (Lexus)

EBD

lectronic Brake Force Distribution prevents the rear wheels from over-braking before the ABS takes effect, or also in certain cases where the ABS is not operating because of possible faults.

EDL

lectronic Differential Lock It makes it possible to start off even on road surfaces which offer differing levels of grip, by braking the wheel which is slipping.

EBC

ngine Braking Control This system prevents the driven wheels from locking as a result of the braking power of the engine if the accelerator peal is released suddenly or if the car is braked with a gear engaged.

Introduction

Two different systems of ESP are used within the Group: – CONTINENTAL TEVES – BOSCH.

For your information a brief description of the fundamental difference between the two systems and the vehicle models in which the different systems are installed, before we concentrate our attention on the ESP in the OCTAVIA.

What is the difference between the two systems?

In order to prevent a vehicle from skidding, a vehicle dynamic system such as ESP must be able to actively control the brakes within a fraction of a second. The pressure is built up by the ABS hydraulic pump. It is important that an adequate pre-pressure exists at the inlet side of the pump in order to improve the delivery of the pump, particularly at low temperatures.

CONTINENTAL TEVES

koda

Octavia* Audi A8

Golf ’98 Audi A6

Audi A3, Audi TT Audi A4

New Beetle Passat ’97

Seat Toledo

It is in how this pre-pressure is produced that a fundamental difference exists between the systems from CONTINENTAL TEVES and BOSCH.

The MK 20 or MK 60 system from

CONTINENTAL TEVES is used on the

koda

Octavia

BOSCH

The system is used in the MK 20 and MK 60 versions. In the MK 20 the prepressure is built up by means of an active brake servo unit, which is also known as an active booster (pre-pressure booster). On the MK 60 the pre-pressure is produced by the ABS hydraulic pump. Hydraulic unit and control unit for ABS with EDL/TCS/ESP form a single unit.

BOSCH systemCONTINENTAL TEVES system

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The pre-pressure is produced by means of a pre-pressure pump. It is known as the vehicle dynamic control hydraulic pump and is located below the hydraulic unit. The control unit for ABS with EDL/TCS/ ESP is separate from the hydraulic unit. More recent BOSCH systems also operate without a pre-pressure pump.

Forces and moments

A body is subjected to different forces and moments. If the total of these forces and moments acting in the body is equal to zero, the body is at rest. If the total is not equal to zero, the body is then moved in the direction of the force resulting from the total.

Physical Principles

The force with which we are most familiar is the force of gravity of the Earth. It acts in the direction of the centre of the Earth. If we suspend a mass weighing one kilogram from a spring balance in order to measure the forces which exist, what is indicated for us is a value for the force of attraction of 9.81 Newton.

The forces which act on a vehicle, are:

the driving force

the braking force, which acts in the opposite direction of the driving force

cornering forces, which maintain the steerability of the vehicle, and

weight (wheel load), which, in combination

with the friction, enable the other forces to be active.

F 9,81 N

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In addition to this, there are the following forces which occur at a vehicle:

– moments, which attempt to turn the

vehicle about its vertical, transverse and longitudinal axis Example I - yaw moment and

– steering moments and moments of inertia,

which attempt to maintain a direction of movement once adopted Example II - wheel moments of inertia as well as other forces such as

– aerodynamic drag, wind force (cross wind),

centrifugal force

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Physical Principles

The interaction of certain of these forces can be described with the aid of the friction circle. The radius of this circuit is determined by the adhesion between the surface of the road and tyre. In other words, if adhesion is low, the radius is less than a, if adhesion is good, it is greater than b. Let us take a look at a wheel of the vehicle for this purpose.

The principle of the friction circle is a force parallelogram made up of the cornering force

, the braking or driving force B and a

resulting total force G.

III

So long as the total force remains within the circle, the vehicle is still within a stable state I. The moment the total force extends beyond the circle, the vehicle is now in the state II which can no longer be controlled.

Let us take a look at the dependencies which exist between the forces:

Figure 1

Braking force B and cornering force S are dimensioned in such a way that the total force

is contained within the circle.

It is possible to properly steer the vehicle.

Figure 2

We increase the braking force B The cornering force S becomes less.

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Figure 3

The total force G is equal to the braking force B. The wheel locks. In the absence of a

cornering force, it is no longer possible to control the vehicle. A similar situation exists between driving force and cornering force. If the cornering forces are reduced to zero by fully exploiting the driving force, the driving wheels spin.

S 0

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Vehicle Dynamic Control

This is how ESP works

If the ESP is to be able to react to critical driving situations, it is necessary to answer two questions:

a - In which direction is the driver steering? b - In which direction is the vehicle travelling?

The system is supplied with the answer to question a by the steering angle sensor 1 and by the speed sensors 2 at the wheels.

The answer to question b is supplied by measuring the yaw rate 3 and the lateral acceleration 4.

The information flowing in is analysed in order to prepare a set/actual comparison. If an inequality of a to b is determined, the ESP proceeds on the basis that a critical situation may arise and a control cycle is necessary.

A critical situation in such a case may express itself in the vehicle behaving in one of two

ways:

I. The vehicle threatens to understeer.

The ESP prevents the vehicle running out of the curve by specifically operating the brake of the rear inner wheel and intervening in the engine and gearbox management system*.

II. The vehicle threatens to oversteer.

The ESP prevents the vehicle from skidding by specifically operating the brake at the front outer wheel and intervening in the engine and gearbox management system*.

Note: Consequently, specified path and actual path are harmonised.

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* Intervention in gearbox management system only

in the case of automatic gearbox.

Vehicle Dynamic Control

As you have seen, ESP is able to counter a tendency for the vehicle to oversteer or understeer. In order to do this, it is necessary to achieve a change in the direction of the vehicle without directly interfering in the steering.

We are familiar with the basic principle of this from tracked (caterpillar) vehicles.

If a tracked vehicle wishes to make a righthand turn, the track on the inside of the curve is braked and the outer track is accelerated.

If it then wishes to turn back into the original direction, the track which was previously on the inside of the curve and is now the outer track is accelerated, and the other track is braked.

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It is on the basis of a similar principle that the

ESP operates. Let us now first of all take a look at a vehicle not fitted with ESP.

The vehicle has to avoid an obstacle which has appeared suddenly in front. The driver first of all steers very rapidly to the left and then immediately to the right again.

As a result of the steering action on the part of the driver, the vehicle sways, and the rear breaks away. The driver is no longer able to control the rotation of the vehicle about its vertical axis.

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Let us now take a look at the same situation with a vehicle fitted with ESP.

The vehicle attempts to avoid the obstacle. On the basis of the data supplied by the sensors, the ESP detects that the vehicle is close to an unstable driving state. The system computes its countermeasures: The ESP brakes the rear left wheel, which in turn assists the rotational movement of the vehicle. The cornering force of the front wheels is maintained.

While the vehicle is negotiating the arc to the left, the driver is steering to the right. The ESP assists this counter-steering action by braking the front right wheel. The rear wheels rotate freely in order to ensure that the optimal cornering forces exist at the rear axle.

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The preceding change of lane can result in the

vehicle swaying about its vertical axis. The left front wheel is braked in order to prevent the rear of the vehicle from swaying out. In particular critical situations the wheel may be braked very sharply and even locked for short periods in order to limit the increase in the lateral forces at the front axle (friction circle).

After all the unstable states of the vehicle have been rectified, the ESP terminates the control cycle.

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System Overview

The system and its components

The electronic stability programme is based on tried-and-tested wheel slip control systems. It enlarges on these, however, in one decisive aspect:

The system is able to detect unstable vehicle states, such as skidding, at an early stage and compensate for this.

In order to achieve this, additional sensors and actuators are required over and above the already familiar control system.

Let us first of all obtain a proper picture of these as achieved on the Octavia, before we delve deeper into the subject of ESP.

Components for MK 20 and MK 60

Components only for MK 20

Brake servo unit with brake master cylinder

MIN

Longitudinal acceleration sensor G249 (only 4x4 models)

Active brake servo unit with brake master cylinder

Components only for MK 60

Brake pressure sensor (at brake master cylinder)

Note: ESP systems exist from various manufacturers. The system used on the Octavia is manufactured by CONTINENTAL TEVES.

Brake pressure sensor (at brake master cylinder)

If the design and basic principle of ESP systems is always identical, the individual components do, however, differ. For this reason, always ensure you use Genuine Replacement Parts.

TCS/ESP pushbutton E256 Steering angle sensor G85

Speed sensors at front and rear wheels G44 ... 47

Control unit for ABS with EDL/TCS/ESP J104 with hydraulic unit

Yaw rate sensor G202

Lateral acceleration sensor G200

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System Overview

CONTINENTAL TEVES

Sensors

TCS/ESP pushbutton E256 (in middle of dash panel)

Brake light switch F

ESP brake recognition switch ESP F83 (in brake servo unit)

- only in the case of MK 20 -

Wheel speed sensors G44, G45, G46, G47

Steering angle sensor G85 (on steering column)

Control unit for ABS with EDL/TCS/ESP J104 in left of engine compartment

Lateral acceleration sensor G200 (at bearing bracket for steering column)

Brake pressure sensor -1- G201 (at brake master cylinder)

Brake pressure sensor G202 (at bearing bracket for steering column)

Brake pressure sensor -2- G214 (at brake master cylinder) - only in the case of MK 20 -

Longitudinal acceleration sensor G251 at right of central tube, close to right A pillar

- only 4x4 models-

Additional signals:

Engine management Gearbox management Haldex clutch - only in the case of MK 60 -

Actuators

ABS hydraulic pump V64

ABS inlet valves N99, N101, N133, N134

ABS outlet valves N100, N102, N135, N136

Electronic stability programme switch valve -1- N225 Electronic stability programme switch valve -2- N226

Electronic stability programme high-pressure valve -1N227 Electronic stability programme high-pressure valve -2N228

Brake pressure solenoid N247 (in brake servo unit)

- only in the case of MK 20 -

Brake light suppression relay J508

- only in the case of MK 20 -

ABS warning light K47

Handbrake/brake fluid level warning light K14/33

Electronic stability programme warning light K155

1/min x 1000

120

100

140

km/h

160

6 7

180

200

220

240

Control unit with display in dash panel insert J218

Voltage supply relay J535 for warning light K155

- only in the case of MK 20 -

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Additional signals:

Engine management Gearbox management Navigation system management

Diagnostic connection

Design and Operation

Control loop

taking the example of MK 20

3 4 5

7 8

Regelung

ESP

ABS

ASR EDS EBV MSR

1413 15 16

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1 Hydraulic unit, with control unit for

ABS with EDL/TCS/ESP

2 Active booster with brake pressure

sensor and release switch

191

3 Longitudinal acceleration sensor

(only 4x4 models) 4 Lateral acceleration sensor 5 Yaw rate sensor 6 TCS/ESP pushbutton 7 Steering angle sensor 8 Brake light switch

9 - 12 Wheel speed sensors

13 Diagnostic cable 14 Handbrake/brake fluid level

warning light

15 ABS warning light 16 Electronic stability programme

warning light

17 Vehicle handling and driver

behaviour

18 Intervention in engine

management

19 Intervention in gearbox

management (only automatic

gearbox models)

The speed sensors constantly supply the speeds for each individual wheel.

The steering angle sensor supplies its information directly over the CAN databus to the control unit. This information is analysed by the control unit in order to calculate the specified steering direction and a specified handling of the vehicle.

The lateral acceleration sensor signals to the control unit if the vehicle is breaking away at the side, while the speed sensor warns of any tendency of the vehicle to skid. These two sources of information are used by the control unit to calculate the actual status of the vehicle.

If the set value and actual value differ from each other, a control cycle is calculated.

The ESP decides:

– which wheel is to be severely braked or

accelerated,

– whether the engine torque is to be

reduced, andund

– whether, on models fitted with an

automatic gearbox, the gearbox control unit has to be activated.

After this, the system verifies how successful the intervention has been on the basis of the data flowing in from the sensors. If yes, the control cycle is ended and the vehicle handling continues to be observed. If no, the control cycle is once again repeated.

If a control cycle is activated, this is indicated to the driver by the electronic stability programme warning light flashing.

Control unit for ABS with EDL/TCS/ ESP J104

The control unit is combined with the hydraulic unit to form a single component.

Function

– Analysing the signals supplied by the ESP

sensors,

– controlling the ESP, ABS, EDL, TCS, EBD

and EBC functions,

– continuously monitoring all the electrical

components, and

– self-diagnosis.

When the ignition is switched on, a selftest of the control unit is then performed. All the electrical connections are constantly monitored and the operation of the solenoid valves is periodically checked.

Effect in the event of a failure

Hydraulic unit

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Control unit J104

In the very unlikely situation of a total failure of the control unit, the driver has available only the normal braking system without ABS, EDL, EBD, EBC, TCS and ESP.

Self-diagnosis

The following faults are detected:

– Control unit faulty – Control unit incorrectly coded – Fault in voltage supply – ABS hydraulic pump faulty – Implausible signals in ABS mode – Drive databus faulty – Fault in sensor circuits

Electrical circuit

The voltage for control unit J104 is supplied directly through the fuse carrier at the battery. The control unit is linked to the databus.

D/15 A+

N99

J104

N136N135

CAN -H

CAN -L

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Design and Operation

Steering angle sensor G85

The sensor is located on the steering column between steering column switch and steering wheel. The restoring ring with coil spring for the airbag is integrated in the steering angle sensor and is located on the underside.

Task

Transmitting the angle by which the driver turns the steering wheel to the left or right, to the control unit for ABS with EDL/TCS/ESP.

The sensor is able to detect an angle of ± 720˚, which represents four full turns of steering wheel.

Effect in the event of failure

In the absence of the information from the sensor, the ESP is not able to detect the desired change in the direction of travel. The ESP function is then no longer operational.

Restoring ring with coil spring for driver airbag

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Note: After carrying out alignment work on the chassis and repair and installation operations on the steering, it is then necessary to carry out a zero compensation. The zero compensation must also be conducted after replacing the brake pressure sensors. For more detailed information please refer to the Workshop Manual.

Electric circuit

The steering angle sensor is the only sensor of the ESP system which transmits its information directly over the CAN databus to the control unit. After the ignition is switched on, the sensor is then initialised once the steering wheel is turned by 4.5˚. This is equal to a rotational movement of the circumference of the steering wheel by about 1.5 cm.

CAN-H

J...

J104

CAN-L

J...

G85

+30D/+15

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Design

The angle is measured using the light barrier principle (opto-electrical signal).

The basic elements are:

a a light source b a coding disc with 2 hole screens c + d optical sensors, and e an indexing unit for complete

revolutions.

The coding disc consists of two rings, the absolute ring and the incremental ring. Both rings are scanned by two sensors each.

Function

Let us simplify the design by positioning an incremental hole screen 1 and an absolute hole screen 2 mixed to each other. Between the hole screens is the source of light 3. The optical sensors 4 + 5 are located on the outside.

If light shines through a gap onto a sensor, a signal voltage is produced. If the source of light is concealed, the voltage again collapses.

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If we now move the hole screens in the direction of the arrow, two different voltage sequences are produced.

The incremental sensor supplies a uniform signal as the gaps follow each other in a regular pattern. The absolute sensor supplies an irregular signal as the holes in the screen are positioned at irregular intervals. The system is able to calculate the extent to which the hole screens have been moved from the comparison of both signals. This makes it possible to determine the starting point of the movement of the absolute part.

The steering angle sensor operates according to the same principle, the only difference being that it is designed for a rotational movement.

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Design and Operation

Lateral acceleration sensor G200

For physical reasons, this sensor should be located as close as possible to the centre of gravity of the vehicle. The installation position and the orientation of the sensor must on no account be altered. It is located on the right next to the steering column and is attached on a bracket together with the yaw rate sensor.

Task

The sensor determines the cornering forces which can be transmitted. In so doing, it supplies an important basis for estimating which vehicle movements can be accomplished under the existing road conditions without creating any vehicle instability.

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Effect in the event of failure

In the absence of the measurement of the lateral acceleration it is not possible to calculate the actual driving state in the control unit. The ESP function is then no longer operational.

Self-diagnosis

Self-diagnosis determines whether an open circuit exists in the wiring or a short circuit to positive or to earth. In addition, the system detects whether the sensor signal is plausible.

Electrical circuit

The lateral acceleration sensor is linked directly to the control unit J104 by three cables.

J104

Note: This sensor is very sensitive to damage.

G200

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Design

The lateral acceleration sensor operates on a capacitive principle.

What does this mean?

Let us imagine that the sensor consists of two capacitors arranged one behind the other. The position of the common, middle capacitor plate can be shifted by the effect of a force.

Each capacitor possesses a capacitance, in other words is able to absorb a certain quantity of electrical charge.

Function

So long as no lateral acceleration is effective, the middle plate maintains the same distance to the outer plates, with the result that the electrical capacitance of the two capacitors is the same.

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The moment a lateral acceleration becomes active, the middle plate is shifted so that the distance to the one plate becomes greater, and to the other plate becomes less. This in turn alters the capacitances of the subcapacitors.

Consequently, the electronic control is able to determine the direction and extent of a lateral acceleration from a change in the capacitances.

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Design and Operation

Yaw rate sensor G202

The necessity for installing this sensor close to the centre of gravity of the vehicle results from the fact that it is mounted together with the lateral acceleration sensor on a bracket.

Task

It determines whether torques are acting on a body. Depending on the installation position, it is then possible to determine a rotation about one of the three-dimensional axes. In the ESP system the sensor has to determine whether the vehicle is turned about its vertical axis. We talk in this case of measuring the yaw rate.

Effect in the event of failure

In the absence of the measurement of the yaw rate it is not possible to detect in the control unit whether the vehicle is developing a tendency to skid. The ESP function is then no longer operational.

Self-diagnosis

The self-diagnosis determines whether an open circuit exists in the wiring or whether there is a short circuit to positive or to earth. In addition, the system detects whether the sensor signal is plausible.

Electrical circuit

The yaw rate sensor is connected directly to the control unit J104 by three cables.

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J104

G202

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Design

The basic element is a micromechanical system with a double tuning fork made of a silicone crystal, which has been housed in a small electronic element on a sensor board.

Let us take a look at a simplified representation of the double tuning fork. It is connected at its "waist" to the other silicone element, which we have omitted here in order to make the illustration clearer to understand.

The double tuning fork consists of an exciter tuning fork and a measuring tuning fork.

Exciter tuning fork

Connection to other silicone body

Measuring tuning fork

Function

If an alternating voltage is applied, the silicone tuning fork can be caused to vibrate with sympathetic oscillations. The two halves are harmonised in such a way

that the exciter tuning fork oscillates in the resonance at exactly 11 kHz and the measuring tuning fork at 11.33 kHz. If an alternating voltage with a frequency of exactly 11 kHz is applied to the double tuning fork, the exciter tuning fork vibrates with sympathetic oscillations, but not the measuring tuning fork.

A tuning fork which is vibrating with sympathetic oscillations, reacts more inertly to the effect of a force than a mass which is not oscillating.

The exciter tuning fork oscillates in resonance

Alternating voltage with a frequency of 11 kHz

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The measuring tuning fork does not oscillate in resonance

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Design and Operation

What this means is:

Whereas the measuring tuning fork and the rest of the sensor moves together with the vehicle when the effect of a rotational acceleration is felt, the oscillating part of the double tuning fork (exciter tuning fork) follows this movement with a certain time lag. Consequently, the double tuning fork turns within itself in the same way as a cork opener.

This turning motion results in a modified distribution of the charge at the tuning fork which is measured by electrodes, analysed by the sensor electronics and transmitted as a signal to the control unit.

Resonance oscillation

Turning moment

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Longitudinal acceleration sensor G251

It is located at the right of central tube, close to the right A pillar. It is required only on 4x4 vehicles.

On vehicles which are driven at only one axle, the system calculates the longitudinal acceleration of the vehicle from the value supplied by the brake pressure sensor, from the signals supplied by the speed sensors at the wheels, and from the information supplied by the engine management system.

On all wheel-driven vehicles with a Haldex clutch, the front and rear wheels are rigidly connected. The calculation of the real vehicle speed, which is determined from the speeds of the individual wheels, may not be sufficiently accurate in certain circumstances if the adhesion which exists between tyre and road surface is low, and the Haldex clutch is closed. The measured longitudinal acceleration is used as confirmation of the theoretically calculated vehicle speed.

Effect in the event of failure

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Note: Design and operation are similar to the lateral acceleration sensor. Relative to the latter, the sensor is installed turned through 90˚, however.

In the absence of the additional measurement of the longitudinal acceleration on 4x4 models, it may no longer be possible, in unfavourable conditions, to reliably calculate the real speed of the vehicle. The ESP and TCS functions are no longer operational. The EBD function is maintained.

Self-diagnosis

Self-diagnosis determines whether an open circuit exists in the wiring or whether there is a short circuit to positive or to earth. In addition, the system detects whether the sensor signal is plausible.

Electrical circuit

The longitudinal acceleration sensor is connected directly to the control unit J104 by three cables.

G251

J104

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Design and Operation

TCS/ESP pushbutton E256

The pushbutton on the Octavia is located in the middle of the dash panel. The driver can operate the pushbutton to switch off the TCS/ ESP function. If the TCS/ESP function is switched off, the TCS/ESP warning light in the dash panel insert comes on and remains on. If the driver presses the pushbutton once again, the TCS/ESP function is reactivated. The warning light goes out. If the driver happens to forget to reactivate the system, the system is reactivated automatically the next time the engine is started.

In normal circumstances, the TCS/ESP should always remain switched on.

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In exceptional cases, when slip at the driving wheels is desired, for example:

– when rocking the vehicle free out of deep

snow or soft ground – when driving with snow chains, and – for operating the vehicle on a chassis

dynamometer

it is beneficial to switch off the ESP system.

It is not possible to switch off the system if an

ESP control cycle is active at that moment. As soon as the ESP commences a control cycle, the TCS/ESP warning light in the display unit of the dash panel insert flashes. This is intended to signal to the driver that the vehicle is moving in a limit situation in terms of the physical limits.

If a fault occurs in the system, the warning light comes on and remains on.

Electrical circuit

D/+15

Effect in the event of failure

If the pushbutton is faulty, it is not possible to switch off the TCS/ESP function.

Self-diagnosis

Faults at the pushbutton are not detected by the self-diagnosis.

E256

24 44

J104

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Brake pressure sensor -1- G201 Brake pressure sensor -2- G214*

The sensors are screwed in at the brake master cylinder.

Task

The task of the sensors is to supply measured values for calculating the braking forces and for controlling the pre-pressure.

Effect in the event of failure

If the control unit does not receive a signal from the sensor, the ESP function is then inactive.

Self-diagnosis

The self-diagnosis determines whether an open circuit exists in the wiring or whether there is a short circuit to positive or to earth. In addition, the system checks whether the signals of the two sensors are plausible.

Electrical circuit

Each of the brake pressure sensors is linked to the control unit J104 by three cables.

J104

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J104

* only in the case of MK 20

G201

G214*

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Design and Operation

Design

The brake pressure sensors are each capacitive sensors.

To better understand how they operate, we also use a simplified illustration of a plate capacitor in the inside of the sensor a, on which the pressure of the brake fluid is able to act.

Function

As a result of the distance s between the two plates, the capacitor has a certain capacitance C. What this means is that it is able to absorb a certain "quantity" of electrical charge. The capacitance is measured in farad.

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One plate is firmly fixed in place. The other can be moved by the pressure of the brake fluid.

Once the pressure acts on the movable plate, the distance between the two plates becomes less and is now s greater and is now C

If the pressure is once again reduced, the plate is pushed back by a compression spring. The capacitance once again becomes less.

, the capacitance becomes

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Consequently, a change in the capacitance is a direct measure for the change in pressure.

SP28-58

Active brake servo unit with brake master cylinder, for MK 20

The active brake servo unit, or active booster, differs fundamentally from older models.

In addition to the usual function of assisting the foot pressure applied to the brake pedal with the aid of a vacuum drawn from the intake manifold, or by means of a vacuum pump, it also performs the task of producing the pre-pressure for an ESP control cycle.

This is necessary as the intake capacity of the ABS hydraulic pump is not always adequate to produce the pressure required.

The reason for this is due to the high viscosity of the brake fluid at low temperatures.

SP28-59

Effect in the event of failure

If the solenoid or the brake detection switch F83 fails, it is no longer possible to make use of the ESP function.

Self-diagnosis

The following faults are detected:

– open circuit in wiring – short circuit to positive or to earth, and – faulty component

Electrical circuit

J104

N247 F83

SP28-60

Design and Operation

Design

Let us first of all take a look at the general design.

The booster consist of a modified brake master cylinder a and the brake servo unit b. The brake servo unit is divided into a vacuum part c and a pressure part d, which are separated by a diaphragm f. In addition, it has a valve plunger-solenoid unit e.

The valve plunger-solenoid unit is connected electrically to the ESP system.

It consists of:

– the ESP brake detection switch F83 – the brake pressure solenoid N247 – various air guide valves, with which we

shall not deal with here in any further

detail, though.

SP28-61

N247

The ESP brake detection switch is also known as a release switch. It is in fact a double-contact switch. If the brake pedal is not operated, the contact is linked to signal contact 1.

Once the brake pedal is operated, the signal contact 2 closes.

The lights 1 and 2 are not physically present. They merely symbolise the electrical circuits which are closed in different situations.

In view of the fact that one contact is always closed, the signal of the switch is always clear.

This makes it possible for the release switch to offer a high level of intrinsic safety.

F83

SP28-62

SP28-63

Function of the valve plunger-solenoid unit

The purpose of the valve plunger-solenoid unit is to build up a pre-pressure of 1 MPa (10 bar) which is required on the inlet side of the ABS hydraulic pump in the event that the driver has not depressed the brake pedal.

If the system detects that an ESP control cycle is necessary and the driver has not yet depressed the brake pedal, the brake pressure solenoid is actuated by the control unit for ABS with EDL/TCS/ESP.

A magnetic field is produced in the solenoid, which attracts a metal core into the solenoid. As a result of this movement, valves within the valve plunger-solenoid unit open and sufficient air flows into the brake servo unit in order to build up the pre-pressure of 1 MPa (10 bar).

SP28-64

If the specified pre-pressure is exceeded, the current to the solenoid is reduced. The metal core slides back and the pre-pressure drops.

The control unit switches off the solenoid at the end of the ESP control cycle, or if the brake pedal is depressed by the driver.

SP28-65

SP28-66

Design and Operation

Function of the ESP brake detection switch F83

The brake detection switch informs the ESP system of whether the driver is applying the brakes.

If the contact is resting against the signal contact 1 in the switch, the system proceeds on the basis that it must ensure by itself that the necessary pre-pressure is built up.

If the driver operates the brake pedal, the solenoid is pushed in the direction of the brake master cylinder.

As a result of this, the contact in the switch moves from signal contact 1 to signal contact 2 and the system becomes aware of the fact that the driver is applying the brakes.

In view of the fact that the pre-pressure is now achieved by the foot pressure of the driver on the brake pedal, the solenoid no longer needs to be actuated.

SP28-67

SP28-68

Brake light suppression relay J508, for MK 20

Once the control unit for ABS with EDL/TCS/ ESP actuates the solenoid in the valve plunger-solenoid unit, it is possible for the brake pedal to move quite severely because of the tolerances which occur in such a case. In certain circumstances, the brake light switch might close the contact to the brake lights.

In order to avoid motorists behind from being irritated in this way, the relay J508 interrupts the link to the lights so long as the solenoid is actuated.

Electrical circuit

Legend

D Ignition/starter switch F Brake light switch J1 04 Control unit for ABS with EDL, TCS,

ESP J508 Brake light suppression relay M9 Bulb for left brake light M10 Bulb for right brake light S Fuse

D/15 +30

23 31

S9 5A

S13 10A

J508

M9 M10

J104

SP28-06

Design and Operation

The hydraulic unit

The hydraulic unit is mounted on a support in the left of the engine compartment. Pump and valve block are combined in a housing and, together with the electric motor, form a single unit. The hydraulic unit is bolted to the control unit. It operates with two brake circuits split diagonally.

Compared to older ABS units, it has been enlarged by a changeover valve and inlet valve for each brake circuit.

The two additional changeover valves are:

– Electronic stability programme switch

valve - 1 - N225 and

– Electronic stability programme switch

valve -2- N226.

Hydraulic unit

SP28-69

The two additional inlet valves are:

– Electronic stability programme high-

pressure valve -1- N227 and

– Electronic stability programme high-

pressure valve -2- N228.

Three different system positions exist:

– building up pressure – maintaining pressure, and – reducing pressure.

The ABS hydraulic pump is self-inducting.

Effect in the event of failure

If faults exist in the hydraulic unit, the ESP system is not active. The ABS function is maintained.

Self-diagnosis

Control unit J104

All the valves and the pumps are constantly electrically monitored. If electrical faults exist, the control unit must be replaced.

Function diagram

taking the example of MK 20

Let us take a look at the wheel in a brake circuit.

The elements are:

a Electronic stability programme switch valve b Electronic stability programme high-

pressure valve

c ABS inlet valve d ABS outlet valve e Wheel brake cylinder f ABS hydraulic pump g Active brake servo unit, and h Low-pressure reservoir

Building up pressure

The booster builds up a pre-pressure in order to enable the ABS hydraulic pump f to draw in the brake fluid. In the case of MK 60 the prepressure is built up directly by the hydraulic pump. The electronic stability programme switch valve a closes. The electronic stability programme highpressure valve b is open. The ABS inlet valve c remains open until the

wheel has been braked as much as necessary.

SP28-70

SP28-71

Maintaining pressure

All the valves are closed.

Reducing pressure

The ABS outlet valve d is open, the electronic stability programme switch valve a is open or closed depending on the pressure level. The electronic stability programme high-pressure valve b and the ABS inlet valve c are closed. The brake fluid flows through the electronic stability programme switch valve a and the brake master cylinder into the reservoir.

SP28-72

SP28-73

Function Plan

taking example of MK 20

D/+15

S9 5A

S15

A/+

S162

30A

S163

30A

4258

J535

58d

L71

E 256

CAN-H

J...

G85

G44/45/46/47

16472444

CAN-L

J...

7/3 33/37

34/36

N99/101/133/134 N100/102/135/136

461522019

G202G200

2711422599 6/4

Components

A/+ Battery/+ D/+15 Ignition/starter switch, terminal 15 E256 TCS/ESP pushbutton F Brake light switch F9 Handbrake indicator switch F34 Brake fluid level warning contact F83 ESP brake detection switch G44-47 Wheel speed sensors G85 Steering angle sensor G200 Lateral acceleration sensor G201 Brake pressure sensor -1-

= Input signal

G202 Yaw rate sensor G214 Brake pressure sensor -2G251** Longitudinal acceleration sensor J … Engine management control unit etc. J104 Control unit for ABS with EDL/TCS/ESP J218 Control unit with display unit in dash panel

insert J503* Navigation system control unit J508 Brake light suppression relay J535 Voltage supply relay for warning light K155

= Output signal

S11 5A

G201

12 28 43 10 26 41 14 30 45 29 13 32 1

N225 N226 N227 N228

G214

J104

G251**

F83

35 235818 4

J503*

J508

N247

K155

39 22

V64

M9 M10

K14/33

K47

J218

F34

K14/33 Handbrake/brake fluid level warning light K47 ABS warning light K155 Electronic stability programme warning light L71 TCS switch illumination M9 Bulb for left brake light M10 Bulb for right brake light N99/101 ABS inlet valves /133/134 N100/102 ABS outlet valves /135/136

= Battery positive

= Earth

SP28-07

N225 Electronic stability programme switch valve -1N226 Electronic stability programme switch valve -2N227 Electronic stability programme

high-pressure

valve -1-

N228 Electronic stability programme high-pressure

valve -2N247 Brake pressure solenoid, in brake servo unit S … Fuse V64 ABS hydraulic pump

Diagnostic connection

* only models with Navigation system ** only 4x4 models

= CAN databus

Self-Diagnosis

Self-diagnosis can be performed with the vehicle system tester V.A.G 1552, the fault reader V.A.G 1551 or with the vehicle diagnosis, measuring and information system VAS 5051.

The address word is:

03 - Brake electronics

X A

N I M

X A

N MI

The following functions are available:

00 - Automatic test sequence 01 - Interrogating control unit version 02 - Interrogating fault memory 03 - Final control diagnosis 04 - Basic setting 05 - Erasing fault memory 06 - Ending output 07 - Coding control unit 08 - Reading measured value block 11 - Login procedure

The interface between the diagnostic tool and the ESP system is the diagnostic connection.

All the colour-coded components of the ESP are integrated in the self-diagnosis.

Wheel speed sensors

If a wheel speed sensor is faulty, the ABS warning light as well as the TCS/ESP warning light are switched on and the relevant systems are switched off. The EBD function is maintained.

If this wheel speed sensor fault occurs during the selftest but no longer once vehicle speed is more than 20 km/h, the warning lights go out.

120

100

140

1/min x 1000

km/h

160

180

200

220

240

SP28-05

Special features

Function 04 "Basic setting" performs three tasks in the case of the ESP:

1. Display group number 001 is required for bleeding the hydraulic unit.

2. Display group number 031 is required for carrying out the operational check of the brake pressure solenoid and of the ESP brake detection switch.

3. Display group numbers 060, 063, 066, 069 are used for carrying out a zero adjustment.

060 - zero adjustment for the steering

angle sensor

063 - zero adjustment for the lateral

acceleration sensor

066 - zero adjustment for the brake

pressure sensor, and

069 - zero adjustment for the longitudinal

acceleration sensor (only 4x4 models).

The zero adjustment has to be carried out if one of the components is replaced.

Please refer to the Workshop Manual of the ŠkodaOctavia for the exact procedure.

Warning lights and pushbutton in diagnosis

If a fault occurs during a control cycle, the system attempts to complete the control cycle as best as possible. After the end of a control cycle, the subsystem in question is switched off and the warning lights come on.

If a fault has occurred and the warning lights are operated, a fault is always stored in the fault memory.

The ESP function can be switched off with the TCS/ESP pushbutton.

Ignition on The warning lights come on.

Warning lights

Handbrake/brake fluid level warning light K14/33

ABS warning light ABS K47

Electronic stability programme warning light K155

K14/33 K47 K155

The warning lights go off after about 3 s if the system o..

TCS/ESP control cycle

TCS/ESP not operational, or TCS/ESP switched off at pushbutton. ABS/EDL and EBD remain active.

ABS/EDL not operational EBD active, all other systems are not in operation, (e.g. only one wheel speed sensor faulty).

ABS/EDL and EBD not operational All systems are not in operation, (e.g. two or more wheel speed sensors faulty).

Brake fluid level too low. All systems are active.

Service

Service, repairs, zero adjustment

All the components of the ESP are maintenance-free.

The self-diagnosis supplies information regarding any component which is faulty.

After replacing the steering angle sensor G85 or control unit J104, for example, it is then necessary to carry out a zero adjustment for the sensor. What this means is that the sensor must learn where the straightahead position of the steering wheel is.

Please refer to the appropriate Workshop Manual for the ŠkodaOctavia for the exact procedure.

Ensure that the yellow dot in the sight glass on the bottom of the steering angle sensor is fully visible. This is an indication that the sensor is in the 0˚ position.

After replacing the brake pressure sensor, lateral acceleration sensor and longitudinal acceleration sensor, if fitted, it is then necessary to carry out the zero adjustment for these sensors with the aid of the vehicle system tester V.A.G 1552, fault reader V.A.G 1551 or with the vehicle diagnosis, measuring

and information system VAS 5051.

The adjustment of the yaw rate sensor is performed automatically.

Handling replacement parts

Please remember that certain of the sensors, such as the yaw rate or lateral acceleration sensor, are highly-sensitive measuring instruments.

SP28-04

For this reason:

– Always transport parts in the

original wrapping and do not unwrap until just before installing.

– Protect parts from bumps and

shocks.

– Do not place any heavy objects on

top of the sensors.

– When installing, ensure that the

sensors are installed in the exact position.

– Observe the rules for cleanliness at

the workbay.

Test Your Knowledge

Which answers are correct? Sometimes only one. But, sometimes also more than one – or all of them!

1. Which statement is correct regarding the longitudinal acceleration sensor?

A. It is required only on 4x4 models. B. It must always be installed at the centre of gravity of

the vehicle.

C. If it is faulty, the ESP and the TCS functions are

switched off. The EBD function is maintained.

2. When is it good practice to switch off the ESP/TCS function?

A. When rocking the vehicle free out of deep snow or soft ground. B. When there is a risk of black ice. C. When driving with snow chains. D. When operating the vehicle on a chassis dynamometer.

3. Which sensor signals to the control unit for ABS with EDL/TCS/ESP that the vehicle is

breaking away at the side:

A. The steering angle sensor. B. The lateral acceleration sensor.

C. The longitudinal acceleration sensor.

4. The vehicle is threatening to oversteer.

How is the ESP system able to stabilise the vehicle again?

A. Only by braking the inside front wheel. B. Only by braking the outside front wheel. C. By braking the outside front wheel and intervening in the engine and gearbox

management systems.

D. By braking the inside front wheel and intervening in the engine and gearbox

management systems.

5. Which components of the system are tested by the self-diagnosis?

A. The ABS hydraulic pump V64. B. The TCS/ESP pushbutton E256. C. The yaw rate sensor G202. D. The lateral acceleration sensor G200.

1. A., C.; 2. A., C., D.; 3. B.; 4. C.; 5. A., C., D.

Answers

ESP Glossary

SI units

SI is the abbreviation for "Système International d'Unités" and is known as the international system of units (SI). It comprises seven basic units from which it is possible to derive all the other physical and chemical SI units.

The basic units are:

Quantity and character Name and in formula character for unit

Length l Metre (m) Mass m Kilogram (kg) Time t Second (s) Electrical current I Amperes (A) Thermodynamic

temperature T Kelvin (K)

Amount of

substance n Mol (mol)

Luminosity I Candela (cd)

Acceleration a

is the change in velocity within the unit of time in terms of amount and direction.

Pressure p

is defined as the force F acting on a unit of area (A); p = F/A.

The unit of pressure is the Pascal (Pa). A different unit, used in certain countries, is the bar. 1 Pa = 1 N/m

Moment M

There are different types of moments. For example we shall take here the turning moment (torque).

in which F is the force in Newton (N) and r the vertical distance of the line of flow of the force from the centre of rotation in metres (m).

Electrical capacitance C

is the capacity for electrical charges, defined as a ratio of the quantity of the charge (Q) to a voltage (U), in other words C = Q/U.

(1 bar = 0.1 MPa = 105 Pa),

Torque M = F · r (Nm)

The unit of measurement m/s

In the case of a linear motion the acceleration consists in an increase in the amount of the velocity. A deceleration (braking) is termed as negative acceleration.

Force F

is a directed physical quantity. It is the cause for a change in shape or for the acceleration of freely moving bodies. A body on which no forces are acting, remains in the state of rest or of uniform linear motion. The state of rest is also achieved if the total of all the active forces is equal to zero. The SI unit of force is Newton (N), 1 N = 1 kg · m/s

The unit of the electrical capacitance (C) is the farad with the character F. The capacitance is dependent on the geometrical arrangement of the conductors and of the dielectric constants of the material surrounding the conductors. Two electrodes separated by a dielectric are known as capacitors, having the capacitance C.

Physical limits

When enjoying all the benefits which ESP offers, we should never forget that no ESP system is able to overcome the laws of physics.

Whoever looks on ESP as an additional tuning instrument for going even faster, will soon discover that even ESP

cannot stop his car from running off the road.

Don't forget! ESP is a system which enhances active safety, but is not

able to change the physical limits.

SKODA Self Study Program 28 – Octavia Electronic Stability Programme (ESP) SSP-28-Octavia-ESP

Specifications and Main Features

Frequently Asked Questions

User Manual