OTHER Self Study Program 231 – Euro On-Board Diagnostic System For petrol engines SSP-231-EOBD-for-petrol-engines

Service.

Self-Study Programme 231

Euro On-Board Diagnostic System

For petrol engines

Design and Function

Now an integral part of emission control and
monitoring in the USA, the On-Board Diagnostics
(OBD II) system will also be introduced within the
European Union under the name
Euro-On- Board Diagnostics (EOBD) from
1st January, 2000. Initially, the system will be
available for petrol engines only, however, a
version for diesel engines will follow in the
foreseeable future.

There are very few differences between
European variant of this diagnostic system and
US OBD II.

The only alterations made were those necessary
to bring EOBD into line with European exhaust
emission legislation. Other noteworthy features
of EOBD are its central diagnosis interface and
self-diagnosis fault warning lamp.

In this Self-Study Programme, we will show you
new monitored vehicle systems and the
associated diagnostics, taking Self-Study
Programme 175 "On-Board Diagnostics II in the
New Beetle (USA)" as the basis. In this way, you
will not have to read through repetitive material.

The Self-Study Programme presents the design
and function of new developments.
The contents are not subject to updating!

NEW Important

Note

Please always refer to the relevant Service Literature for
current inspection, adjustment and repair instructions.

2

Table of contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Legal framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Overview of EOBD . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

New vehicle systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

EOBD variants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Basic types of engine control unit . . . . . . . . . . . . . . . . 15

Engine control units and diagnostics . . . . . . . . . . . . . 17

Diagnostic routines . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Self-diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Readiness code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Generic Scan Tool

(OBD visual display unit) . . . . . . . . . . . . . . . . . . . . . . . 33

Vehicle Diagnostic, Testing and

Information System VAS 5051 . . . . . . . . . . . . . . . . . . . 35

Function diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Test your knowledge . . . . . . . . . . . . . . . . . . . . . . . . . 44

3

Introduction

Legal framework

On 13th October 1998, the European Union passed the EU Directive 98/69/EC, according to which the
introduction of EOBD is mandatory for all member countries. This directive has been adopted into
national law in the Federal Republic of Germany.

The introduction of EOBD is not directly coupled with an exhaust emission standard of the European
Union (EU II, EU III, EU IV) or the Federal Republic of Germany (D2, D3, D4). Therefore, the target date
for the introduction of OEBD and the associated transition period must be considered independently of
the various exhaust emission standards.

Target date for introduction of EOBD

With effect from the 1st January, 2000, the automobile industry will be required to perform only one type
test for new petrol-engined models if they have EOBD.

Transition period

The transition period pertains to models which have been type-tested prior to 31st December, 1999 and
meet the EU II, D3 or D4 exhaust emission standard. The buyer may still register these vehicles until
31st December, 2000 and operate them without EOBD with no restrictions. With effect from this date,
existing models will be required to have EOBD for initial registration purposes (buyer).

The EOBD legislation does not affect vehicles which were registered by the buyer prior
to 31st December, 1999.

New models

without EOBD

Type tests in the automobile industry

New models

with EOBD

Year 2000 Year 2001

New vehicles

without EOBD

New vehicles without EOBD

(with EU II, D3 or D4)

New vehicles

with EOBD

231_002

Homologation of new vehicles of buyers

4

Overview of EOBD

The visible elements of EOBD are the self-diagnosis fault warning lamp K83 and the diagnosis interface
in the passenger cabin. The engine control unit performs all other functions and diagnostic operations
automatically. The driver does not notice the ongoing checks on the systems in his vehicle which are
relevant to exhaust emissions. This means that not much changes for the driver of a vehicle with EOBD,
however service personnel will be required to familiarize themselves with new automotive technologies
and the associated procedures.

Self-diagnosis fault warning lamp K83

If a fault impairing exhaust gas quality occurs on
board the vehicle, the fault is saved to the fault
memory and the self-diagnosis fault warning
lamp is activated.

EOBD stores the "on" period of the self­diagnosis fault warning lamp (in terms
of kilometres travelled).

EOBD checks:

231_012

231_011

If there is a risk of catalyst damage due to
misfiring, the self-diagnosis fault warning lamp
flashes.

Diagnosis interface

Stored EOBD data can be read out via the
diagnosis interface. The fault codes are
standardised so that data can be acquired using
any Generic Scan Tool (OBD visual display unit).

The diagnosis interface must be within easy
reach of the driver's seat.

- The electrical functions of all components
which are important for exhaust gas quality.

- The functioning of all vehicle systems which
have a bearing on exhaust gas quality
(e.g. lambda probes, secondary air system).

- The functioning of the catalyst.

- For misfiring.

- The CAN databus.

- For trouble-free operation of the automatic
transmission.

5

Introduction

New vehicle systems

Before we describe the details of EOBD to you, it is worth mentioning the new vehicle systems. Since the
publication of the Self-Study Programme 175 "On-Board Diagnostics II in the New Beetle USA", several
vehicle systems monitored by EOBD have been improved.

For functional descriptions of the vehicle systems which are not described in detail in this
Self-Study programme, please refer to Self-Study Programme 175.

The broadband lambda probe

(LSU – Lambda Probe Universal) is a new
generation of lambda probes that are deployed
before the catalyst.
The name reveals the goals that were set for the
development of this probe. The lambda value is
represented by near-linear rises in current, and
no longer by an abruptly rising voltage curve
(which is the case with the step type lambda
probe). As a result, it is possible to measure the
lambda value over a larger measurement area

(broader band).
The conventional finger probes
(LSH – Lambda Probe Heating) or
Planar Lambda Probe (LSF – Lambda Probe Flat)
are also known as step probes because of their
step-like voltage curves.

A step type lambda probe is used for the probe
after the catalyst.
The step-like measurement area of a step type

lambda probe around the value lambda=1 (λ=1)

is sufficient for the probe after the catalyst to
perform its monitoring function.

Broadband lambda probe

Ι

rich

mixture

λ≈1

Current Ι

Step type lambda probe

U

rich

mixture

lean

mixture

231_005

Lambda

lean

mixture

231_004

λ≈1

Volt age U

Lambda

6

● Function

The broadband lambda probe acquires and evaluates lambda values differently to the step type
lambda probe. Therefore, the lambda value is determined from a change of current, not from a change
of voltage. However, the physical processes are identical.

To show the functional differences clearly, both systems are described briefly below.

Step type lambda probe

Ambient air

Probe voltage

The core of this probe is a ceramic body coated
on both sides (Nernst cell). These coatings act as

mV

electrodes; one electrode layer is in contact with
the ambient air and the other is in contact with
the exhaust gas. The differential between the
oxygen concentration in the ambient air and in
the exhaust gas results in a voltage between the
electrodes. This voltage is evaluated in the

Exhaust gas

Electrodes

Engine control unit

engine control unit in order to determine the
lambda value.

Exhaust gas

Diffusion

duct

Ambient air

Measurement area

Pump cell

Pump current

A

450

mV

Probe voltage

231_032

Broadband lambda probe

This probe also uses two electrodes to generate a
voltage, which is the result of different oxygen
concentrations. The difference to the step type
lambda probe is that the voltage of the
electrodes is kept constant. A pump cell
(miniature pump) supplies the electrode on the
exhaust side with enough oxygen to maintain a
constant voltage of 450 mV between the two
electrodes. The engine control unit converts the
power consumption of the pump into a lambda
value.

231_033

7

Introduction

● Examples showing how the

broadband lambda probe is controlled

The fuel/air mixture is becoming leaner. This
means that the oxygen content in the exhaust gas
is rising and the pump cell, while operating at a
constant delivery rate, is pumping more oxygen
into the measurement space than can escape
through the diffusion duct. As a result, the
oxygen-to-ambient air ratio changes and the
voltage between the electrodes drops.

A

450

mV

To restore the voltage between the electrodes to
450 mV, the oxygen content must be reduced on
the exhaust side. To achieve this effect, the pump
cell must pump less oxygen into the measurement
space. The pump delivery rate, therefore, is
reduced until the voltage is restored to 450 mV.

The engine control unit converts the power
consumption of the miniature pump into a
lambda control value and alters the mixture
composition accordingly.

231_036

A

450

mV

231_037

8

450

mV

If the fuel/air mixture is too rich, the oxygen
content in the exhaust gas drops. As a result, the
pump cell, while operating at a constant delivery
rate, is delivering less oxygen into the measuring

A

area and the voltage between the electrodes is
rising.
In this case, more oxygen is escaping through the
diffusion duct than the pump cell can deliver.

231_038

The delivery rate of the pump cell must be
increased in order to increase the oxygen content
in the measuring area. As a result, the electrode
voltage is restored to 450 mV and the power

A

consumption of the pump cell is converted into a
lambda control value by the engine control unit.

The pump action of the pump cell is a purely physical process. No mechanical components are
used for the function. The pump cell is represented above symbolically.
A positive pump cell voltage attracts negative oxygen ions through the oxygen-permeable
ceramic material.

The broadband lambda probe and the engine control unit are a single system. It is important
that the lambda probe matches the engine control unit.

450

mV

231_039

9

Introduction

● Design

Sensor element in cross section

231_042

1 Nernst cell with electrodes
2 Probe heater
3 Ambient air duct
4 Measurement space
5 Diffusion duct

Two makes of lambda probe are fitted.

5

Pump cell with electrodes

a

4

1

2

a Electrode (anode)
b Current source
c Ceramic material
d Electrode (cathode)

3

Symbolic representation

b

c

d

● Electrical circuit (NTK)

● Effects of failure of probe before catalyst

If the signal from the lambda probe fails, no
lambda control takes place and lambda
adaption is disabled.
The fuel tank purging system enters emergency
running mode.
The secondary air and catalyst diagnoses are
disabled.
The engine control unit uses a mapped control as
an emergency function.

J . . .

G39

231_052

● Electrical circuit (Bosch)

J . . .

G39

231_059

The broadband lambda probe may
only be replaced complete with cable
and connectors.

10

231_046

Exhaust gas recirculation valve N18 (new version)

Electrical exhaust gas recirculation system

The exhaust gas recirculation system is primarily
used to increase fuel efficiency in low­displacement engines.
As a result of the recirculating exhaust gases, the
engine is required to induce less air. The resulting
savings in suction work improve fuel efficiency.

1

4

1 Engine control unit J...
2 Exhaust gas recirculation valve N18
3 EGR valve
4 Catalyst

● Function

Two valves were previously used to control the
exhaust gas supply:

2

- Exhaust gas recirculation valve N18

3

-EGR valve

The EGR valve was activated electrically by the
engine control unit and transferred a
corresponding vacuum to the EGR valve.
The vacuum caused the EGR valve to open,
allowing exhaust gas to enter the intake
manifold.

231_047

11

Introduction

Only one valve is still used for electrical exhaust
gas recirculation:

- Exhaust gas recirculation valve N18

This valve is activated directly by the engine
control unit and electromagnetically adjusts the
opening stroke for exhaust gas recirculation.
The integrated exhaust gas recirculation
potentiometer signals the actual opening stroke
of the valve to the engine control unit.

The EGR valve and the exhaust gas recirculation valve are combined in the electrical exhaust
gas recirculation system.

3

1

4

1 Engine control unit J...
2 Exhaust gas recirculation valve N18 and

exhaust gas recirculation potentiometer G212
3Vent
4 Catalyst

2

231_043

● Electrical circuit

N18 G212

++

J . . .

● Effects of failure of valve

If the valve fails in the open position, the engine
shuts down at idling speed and can no longer be
started.
If the valve remains closed, the failure has no
effects on vehicle operation.
The fault will nevertheless be detected and
saved.

231_056

12

Electric throttle drive

The throttle valve was previously adjusted mechanically by means of a Bowden cable. The throttle valve
was only actuated by electric motor when the engine was running at idling speed or when a cruise
control system was in use. Use of the electrical throttle control enables the engine control unit to adapt
the throttle valve position to the given basic conditions in any driving situation.

● Function

The driver's preference or the signals from the
accelerator pedal module are transferred to the
engine control unit. Making allowance for all
auxiliarysignals, the engine control unit then
determines how the torque requirement can best
be implemented.

For example, auxiliary signals are supplied by:

- The cruise control system,

- The air conditioning system,

- The idle speed control,

-The lambda control,

- The automatic transmission and

-ABS/ESP.

The torque requirement is implemented via the
electromotively adjustable throttle valve, the
ignition system and the fuel injection system.

Malfunctions are indicated via the electric
throttle control fault lamp.

For detailed information regarding the

electric throttle drive, please refer to

Self-Study Programme 210.

Auxiliary signals

Throttle valve

control unit J338

fuel injection

Ignition,

Accelerator pedal

module

Electric throttle control fault

lamp K132

(EPC = Electronic Power Control)

231_008

13

Introduction

Integrated shaft sealing ring sensor

In several engines, a new Generation of engine speed sender G28 is in use – the “Integrated shaft
sealing ring sensor” (IWDS – Integrierter Wellendichtring-Sensor).

The sender is mounted in a sealing flange for the crankshaft on the gearbox side of the engine.
The sender wheel (60-2 teeth) is press-fitted on the crankshaft in a precisely defined position.
The IWDS systems are made by two different manufacturers and, therefore, may differ in terms of
their design.

Crankshaft

Gearbox side

Sender wheel

Sealing flange

Engine speed sender G28

Engine side

231_030

Crankcase

14

● Electrical circuit ● Effects of failure

Maximum engine speed is reduced and the

J . . .

engine control unit calculates a default value for
engine speed from the signal supplied by
Hall sender G40.

231_031

G28

EOBD variants

The description and explanation of EOBD is more detailed than the descriptions of individual
components or systems. The difficulties involved quickly become apparent when one considers that
EOBD is not an integrated vehicle system; many individual systems and components are continously
checked for correct functioning. The various vehicle types, engines, engine control units, etc., also have to
be taken into account.

To simplify matters, we will provide you with an overview of the various types of engine control unit and
engine control units before explaining the test procedures.

Basic types of engine control unit

Basically, engine management systems are classified according to how operating states in the intake
manifold (air mass or intake manifold pressure) are determined. This classification is not referred to
specific engine control unit manufacturers, because they usually supply both types.

The intake air quantity or intake manifold pressure are required to calculate

- The ignition point

- The injection quantity

- And for EOBD monitoring of almost all components.

Intake manifold pressure systems

Ignition

Intake manifold pressure
sender G71

Injection

In these engine management systems, intake air
quantity is determined with the aid of the intake
manifold pressure sender.
These systems do not have an air-mass flow
meter.

EOBD

231_034

15

EOBD variants

Air mass systems

As the name suggests, the task of the air-mass
flow meter is to determine the intake air quantity.
The intake manifold pressure sender is no longer
required for this purpose.

Ignition

Air-mass flow meter
G70

Injection

EOBD

231_035

Turbocharged engines have air-mass flow meters and intake manifold pressure senders
because the intake manifold pressure sender is also required to measure the charge pressure.

Engine control units and air flow metering

The various engine control units will now be assigned to the types of engine control unit (air flow

metering in intake manifold).

Bosch Motronic ME 7.5.10 Intake manifold pressure

Bosch Motronic ME 7.1 Air mass

Bosch Motronic ME 7.5 Air mass

Bosch Motronic ME 5.9.2 Air mass

Magneti Marelli 4LV Intake manifold pressure

Engine control units Air flow metering

16

Siemens Simos 3 Air mass

Engine control units and diagnostics

In the following table, the individual EOBD diagnostic routines are assigned to the engine control units.
It can be seen that not all engine control units use the same diagnostic routines within the EOBD.

Engine control units

Diagnostic routines

Comprehensive Components Monitoring

Voltage curve shift and adaption of probe before
catalyst

Lamdba probe heater diagnosis

Reaction time diagnosis of
probe before catalyst

Control limit diagnosis of
probe after catalyst

Motion diagnosis of
probe after catalyst

Catalytic conversion diagnosis

Fuel tank purging system
Flow rate diagnosis

Fuel tank purging system
Modulation diagnosis

Misfiring
Irregular running method

Misfiring
Moment analysis method

Exhaust gas recirculation
Pressure diagnosis

Electric throttle drive

Siemens

Simos 3

Magneti

Marelli 4LV

Bosch

Motronic

M 5.9.2

CAN databus
Data diagnosis

Secondary air
Flow rate diagnosis

Charge pressure limit diagnosis

17

EOBD variants

Engine control units

Diagnostic routines

Comprehensive Components Monitoring

Voltage curve shift and adaption of
probe before catalyst

Lamdba probe heater diagnosis

Reaction time diagnosis of
probe before catalyst

Control limit diagnosis of
probe after catalyst

Motion diagnosis of
probe after catalyst

Catalytic conversion diagnosis

Fuel tank purging system
Flow rate diagnosis

Fuel tank purging system
Modulation diagnosis

Misfiring
Irregular running method

Misfiring
Moment analysis method

Exhaust gas recirculation
Pressure diagnosis

Electric throttle drive

Bosch

Motronic

ME 7.1

Bosch

Motronic

ME 7.5

Bosch

Motronic

ME 7.5.10

18

CAN databus
Data diagnosis

Secondary air
Flow rate diagnosis

Charge pressure limit diagnosis

Diagnostic routines

Many of the diagnostic routines were previously explained and described in
Self-Study Programme 175. To avoid repetition, new diagnostic routines will be
dealt with in detail and known routines will be mentioned only. Known routines
are indicated by a red "icon" and the text "SSP 175".

Comprehensive Components Monitoring

(Line-conducted faults)

This diagnostic routine monitors the functioning of all sensors, actuators and
output stages that are relevant to exhaust emissions within the framework
of the EOBD.
For details of the individual components, refer to the function diagrams.

SSP 175

SSP 175

Components are tested according to the following criteria:

- Check of input and output signals (plausibility)

-Short circuit to earth

- Short circuit to positive

-Open circuit

Lambda probe

Voltage curve shift diagnosis and adaption of the probe before the catalyst

Ageing or poisoning can cause a shift in the voltage curve of the probe before the
catalyst. This shift is detected by the engine control unit and can be compensated
(adapted) within defined bounds.The diagnosis sequence is basically the same
despite the new broadband lambda probe.

SSP 175

Lamdba probe heater diagnosis

By measuring the probe heating resistance, the engine control unit checks the
heat output of the lamdba probe heater for correctness.

SSP 175

19

Diagnostic routine

Reaction time diagnosis of probe before catalyst

The reaction time of the probe before the catalyst can also deteriorate due to ageing or poisoning.

The procedure for diagnosis of these faults was previously explained in Self-Study Programme 175.
However, the signals from the probe before the catalyst have changed due to the use of broadband
lambda probes. Hence, the description of this diagnosis routine with the current signals from probe
before the catalyst.

Modulation of the fuel/air mixture by the engine
control unit is prerequisite for reaction time
diagnosis. This modulation takes the form of
slight fluctuation between lean and rich mixture.
It is induced artificially by the engine control unit,
because the lambda value can be controlled by
using the broadband lambda probe to such as
high degree of accuracy that it is possible to
maintain a constant value of λ=1. For optimal
operation, however, the catalyst requires the
mixture composition to fluctuate slightly.
Therefore, the engine control unit modulates this
mixture when a broadband lambda probe is
being used.

The signal from the broadband lambda probe is specified here as voltage U, because the
Vehicle Diagnostic, Testing and Information System VAS 5051 converts the actual output signal
(current intensity Ι) into a voltage and displays this value.

Mixture modulation of the engine control unit

U

rich mixture

lean mixture

t

U = voltage, t = time

λ=1

231_048

20

● The signal from the probe before the catalyst

follows modulation of the fuel/air mixture by
the engine control unit.

● The signal from the probe before the catalyst

can no longer follow modulation of the
fuel/air mixture.

1

U

U = voltage, t = time

U

t

Probe before

catalyst OK

231_044 231_045

32

Probe before

catalyst not OK

U

t

1 Engine control unit
2 Probe before catalyst
3 Probe after catalyst

U

t

t

21

Diagnostic routines

Control limit diagnosis of probe after catalyst

When the fuel/air mixture is of optimal composition, the voltage of the probe after the catalyst will be in
the region of λ=1. If the probe after the catalyst produces a higher or lower average voltage, this
indicates that the fuel/air mixture is too rich or too lean. The engine control unit therefore changes its
lambda control value (this affects the fuel/air-mixture composition) until the probe after the catalyst
again signals λ=1. This lambda control value has defined control limits. If these control limits are
exceeded, EOBD assumes that there is a fault in the probe after the catalyst or in the exhaust system
(secondary air).

● Lean fuel/air mixture and correct control

The probe after the catalyst signals a rise in oxygen
concentration in the exhaust gas to the engine
control unit through a voltage reduction. The engine
control unit then increases the lambda control value,
and the fuel/air mixture is enriched. The voltage of
the probe after the catalyst rises and the engine
control unit is again able to reduce the lambda
control value. This control loop extends over a
lengthy vehicle operating period.

● Lean fuel/air mixture and reaching of control limit

value

In this case, too, the probe after the catalyst signals
a rise in oxygen concentration in the exhaust gas to
the engine control unit through a voltage reduction.
The engine control unit then increases the lambda
control value, and the fuel/air mixture is enriched.
Despite this enrichment of the fuel/air mixture, the
probe voltage remains low (due to the fault) and the
engine control unit continues to increase the lambda
control value until the control limit is reached and
the fault is detected.

Control loop after

catalyst OK

1

m

m = lambda control value, U = voltage, t = time

m

U

λ=1

t

2

Control loop after

catalyst not OK

U

λ=1

t

231_015

t

231_014

t

22

1 Engine control unit
2 Probe after catalyst

Motion diagnosis of probe after catalyst

The operating performance of the probe after the catalyst is monitored also. To this end, the engine
control unit checks the signals from the probe in acceleration and overrun modes.
When the vehicle is accelerating, the fuel/air mixture is rich, the oxygen concentration in the exhaust gas
decreases and the probe voltage must rise. In overrun mode, the exact opposite applies: fuel feed is off,
the oxygen concentration in the exhaust gas increases and the probe voltage must drop. If the probe
after the catalyst does not react as expected, the engine control unit assumes that the probe after the
catalyst is defective.

● Example: vehicle acceleration

1

v

U

t

v = vehicle road speed, U = voltage,

t = time

1 Engine control unit
2 Probe after catalyst

Probe after catalyst

OK

231_016 231_017

2

Probe after catalyst

not OK

v

t

U

t

t

Catalyst

Catalytic conversion diagnosis

The engine control unit compares the voltages of the probes before and after the
catalyst. In this way, the degree of efficiency - and hence the performance - of the
catalyst can be determined.

SSP 175

23

Diagnostic routines

Fuel tank purging system

Flow rate diagnosis

When the fuel tank purging system is activated, the fuel/air mixture changes.
If the activated charcoal canister is full, the mixture will be rich. If the activated
charcoal canister is empty, the mixture will be lean. This change of mixture
composition is registered by the probe before the catalyst and serves as
confirmation that the fuel tank purging system is functioning properly.

Modulation diagnosis

This diagnosis routine carries out checks cyclically. The engine control unit opens and closes activated
charcoal filter system solenoid valve 1 slightly at defined intervals. The intake manifold pressure sender
records the intake manifold pressure "modulated" in this way and sends this pressure value to the engine
control unit where it is correlated and evaluated.

SSP 175

1

a

4

3

a = opening stroke of solenoid valve

2

t = time, P = pressure

1 Engine control unit
2Tank
3 Activated charcoal canister

Fuel tank purging

system OK

P

t

Fuel tank purging

system not OK

231_009 231_010

a

t

5

4 Activated charcoal filter system solenoid

valve N80
5 Intake manifold pressure sender G71

P

t

t

24

Cylinder-selective misfiring detection system

Irregular running method

The engine speed sender can recognise irregularities in engine speed caused by
misfiring with the aid of the crank disk.
In combination with the signal from the Hall sender (camshaft position), the
engine control unit can locate the cylinder in question, save the fault to fault
memory and activate self diagnosis fault warning lamp K83.

Moment analysis method

As with the irregular running method, the moment analysis method recognises cylinder-selective misfiring
from the signal supplied by the engine speed sender and the Hall sender. The difference between these
two methods lies in the way the engine speed signal is evaluated. The moment analysis method
correlates the irregular engine speed caused by ignition and compression with fixed calculations in the
engine control unit. The basis for these calculations is the engine load and engine speed dependent
torque, the centrifugal mass and the resulting engine speed characteristic.
The fluctuation in engine moment calculated in this way is equally as conclusive as the results of the
irregular running method, but the engine speed characteristic is required to be analysed for each engine
and stored in the engine control unit.

SSP 175

Compression ratio in cylinder 1

n

n = engine speed, t = time

● Irregular engine speed

For the sake of simplicity, only the 1st cylinder
will be examined in this example.

During the compression cycle, the kinetic
energy of the engine is used to compress the
fuel/air mixture. Engine speed decreases.

t

231_018

25

Diagnostic routine

The compression cycle is followed by the ignition
cycle, and engine speed is increased. In this way,
engine speed is made to fluctuate by
compression and ignition during each
combustion cycle.

When all four cylinders are examined, the
individual engine speed fluctuations are
superposed to produce a resulting curve.
This curve is measured by the engine speed
sender and checked by the engine control unit
against a calculation made with characteristic
engine data.

● Misfiring detection using the engine speed signal

no

misfiring

Ignition in 1st cylinder

n

t

231_019

misfiring

1

n

2

n = engine speed, t = time

If the EOBD exhaust emission limits are exceeded due to misfiring, then the self diagnosis fault
warning lamp will be lit continuously.
If, however, there is a risk of misfiring causing damage to the catalyst and the engine is running
within the critical load RPM range, the self diagnosis fault warning lamp initially flashes and a
short time later the fuel feed to the corresponding cylinders is shut off.

n

t

231_020 231_021

1 Engine control unit
2 Engine speed sender G28

t

26

Electrical exhaust gas recirculation

Pressure diagnosis

While exhaust gas is admitted into the intake manifold, the intake manifold pressure sender must register
a rise in pressure (less partial pressure). The engine control unit compares the pressure rise in the intake
manifold with the supplied exhaust gas quantity and can thus determine whether the exhaust gas
recirculation (EGR) system is functioning properly. This diagnosis is only carried out in overrun mode,
because injection is deactivated as a disturbing influence for measurement and the intake capacity of
the engine is very high.

1 Engine control unit

EGR

OK

1

P+

t

P+

EGR

not OK

2 EGR valve N18
3 Intake manifold

pressure sender G71

t

P-

2

3

P+ = excess pressure, P- = vacuum, t = time

231_022

Electric throttle drive

The EOBD uses the electrical throttle control diagnostic
functions which indicate a fault via the electric throttle control
fault lamp.
If these faults still exist during the next one or two driving
cycles, the EOBD also activates the exhaust gas
warning lamp.

The electric throttle drive checks:

- the function processor in the engine control unit

- the accelerator position sender

- the angle senders for throttle valve drive

- the brake light switch

- the brake and clutch pedal switch

- the vehicle road speed signal

P-

231_023

For more detailed information
relating to the diagnostic
functions of the electrical
throttle control, please refer to
Self-Study Programme 210.

27

Diagnostic routines

CAN databus

Data diagnosis

Each engine control unit knows the electronic
components which exchange information via the
CAN databus in the vehicle. If the minimum
number of messages is not received from a
component, a fault is detected and saved.

● CAN databus in proper service condition

All connected components
(in this case: control units) regularly transmit
messages to the engine control unit.
The engine control unit recognises that no
messages are missing and data is being
exchanged properly.

Further components which the CAN databus
uses include:

- Control unit with display unit in the

dash panel insert

- ABS control unit/ESP

- Automatic gearbox control unit

● CAN databus interrupted

A component cannot transmit information to

the engine control unit. The engine control

unit notices the missing information, identifies

the component affected and saves a

corresponding fault message to fault memory.

1

2

A

1 Engine control unit
2 CAN databus

CAN databus

OK

231_024 231_025

BC

CAN databus

not OK

ABC

A-C Various control units on board the vehicle

28

Secondary air system

The performance of the secondary air system was previously tested via the lambda control value.
This means that the voltage present at the probe before the catalyst must indicate a lean mixture during
secondary air discharge (λ>1) although the engine control unit is running the engine on a rich mixture.

Flow rate diagnosis

Since the introduction of the broadband lambda probe, the signal from the probe before the catalyst is
used for diagnosis purposes, because the broadband lambda probe supplies more detailed
measurement results than the step type lambda probe for example. The actual air mass flow is calculated
and checked on the basis of the lambda differential (lambda value before and during secondary
air discharge).

Secondary air

1

2

4

3

5

6

λ = lambda, t = time

1 Engine control unit
2 Secondary air pump relay J299
3 Secondary air inlet valve N112

system OK

λ

Secondary air

system not OK

231_026 231_027

λ

t

4 Secondary air pump V101
5 Combi valve
6 Probe before catalyst

t

29

Diagnostic routine

Charge pressure control

Charge pressure limits diagnosis

In turbocharged engines, charge pressure is checked for exceeding the maximum permissible value
within the framework of the EOBD. The check also serves to protect the engine, which must not be
overloaded by excessively high charge pressure.

● The charge pressure limit is exceeded

The maximum permissible charge pressure is
exceeded due to a fault in the charge
pressure control. The intake manifold pressure
sender signals the presence of charge
pressure to the engine control unit, and the
engine control unit detects the fault.

1

Charge pressure

control not OK

P

● The protective function is initiated

In this case, it is not enough to indicate and

save the fault. The exhaust gas turbocharger

has to be deactivated in order to avoid

damaging the engine. For this purpose, the

"waste gate" of the turbocharger is opened

and the driving exhaust gases are diverted

through it.

Charge pressure

control not OK

231_028 231_029

P

30

2

5

3

Exhaust gas

4

1 Engine control unit
2 Solenoid valve for charge pressure control N75
3 Exhaust gas turbocharger with charge pressure

control valve

t

P = pressure

t = time

4 Waste gate
5 Intake manifold pressure sender G71

t

Notes

31

Self diagnosis

Readiness code

All electrical components are continuously
checked for proper functioning within the
framework of the EOBD. In addition, integrated
systems (e.g. exhaust gas recirculation system)
are checked by non-continuous diagnostic
routines.
The readiness code is set to check
whether these diagnoses were performed or not.
The readiness code consists of an 8-character
number code; a 0 (diagnosis performed) or a 1
(diagnosis not performed) can be assigned to
each digit position.

The engine control unit sets the readiness code
when:

- the readiness code is cancelled

- the engine control unit is put into operation
for the first time.

Vehicle self diagnosis

Select diagnostic
function

02- Interrogate fault memory

03 - Actuator diagnosis
04 - Basic setting
05 - Clear fault memory
06- End of output
07 - Code control unit
08- Read data block
09 - Read individual measured value
10 - Adaptation
11 - Login procedure
15 - Readiness code

01 - Engine electronics
036906034BB
Marelli 4LV 3253
Code 31
Dealership number 5

Vehicle self diagnosis

15 - Readiness code

10100001 Test not complete

The readiness code does not check for faults
occurred; it indicates only whether diagnoses
were performed.
If the diagnoses produce no erroneous entries,
the systems are in proper service condition.

Care should be taken to ensure that the
fault memory is not erased
unnecessarily, because this also causes
the readiness code to be reset or
erased.

01 - Engine electronics
036906034BB
Marelli 4LV 3253
Code 31
Dealership number 5

32

231_058

Test
Instruments

Go to Print

The readiness code marked above represents the
performance status of the following systems in the
given order:

1. Catalyst

2. Catalyst heating

3. Fuel tank purging system

Test
Instruments

Go to Print Help

4. Secondary air system

5. Air conditioning system

6. Lambda probe

7. Lamdba probe heater

8. Exhaust gas recirculation

Unused digit positions of the readiness code are generally set to "0", because not all diagnoses
are available in all vehicles.

Read out readiness code

There are two possible ways to read out the readiness code.

- Using any Generic Scan Tool (OBD visual display unit) or

- Using the Vehicle Diagnostic, Testing and Information System VAS 5051.

The procedures are explained on the following pages.

Generate readiness code

The readiness code can only be generated by running the diagnoses.
There are three possible ways to do this:

- Perform an NEFZ ("Neuer Europäischer Fahrzyklus" = new European driving cycle).
However, the standard workshop will be unable to perform the NEFZ on a roller dynamometer upon
completion of repair work.

- Run the vehicle in average operating mode for long enough
(this may necessitate several trips).

- Using the VAS 5051 diagnostic system, perform a defined test routine (short trip) for each relevant

vehicle system.
The procedure is also explained in "Vehicle Diagnostic, Testing and Information System
VAS 5051".

Generic Scan Tool (OBD visual display unit)

It must be possible to read out emission-related faults and data acquired by the engine control unit
within the framework of the EOBD using any OBD visual display unit. Therefore, the detected faults are
saved using an SAE code. This SAE code is used by all OBD systems.

SAE code:

-P0xxx: Codes with set fault texts defined by the SAE (Society of Automotive Engineers)
(same for all automobile manufacturers)

-P1xxx: Codes defined by automobile manufacturers which are required to be reported to the
government (these codes are defined differently for different automobile manufacturers)

33

Self diagnosis

An OBD visual display unit can be put into
operation simply by connecting it to the
diagnosis interface in the passenger cabin.
Communications between the engine control unit
and OBD visual display unit will be established
automatically.

For fault tables for the SAE codes, refer
to the Workshop Manual of the relevant
engine control unit.

re. Mode 3 and 7:
For fault acknowledgement, several
diagnosis routines require one or more
trips until the self diagnosis fault
warning lamp is activated.

An OBD visual display unit facilitates the
following functions:

-Mode 1:
Read out current engine operating data
(actual data, readiness code).

-Mode 2:
Read out operating conditions which existed
while saving a fault
(only used if a fault has occurred).

-Mode 3:
Read out emission-related faults which have
caused the self diagnosis fault warning lamp
to be activated.

-Mode 4:
Erase fault code, readiness code and
operating conditions (Mode 2).

-Mode 5:
Display lambda probe signals.

-Mode 6:
Display measured values of non-permanently
monitored systems (e.g. secondary air system,
fuel tank purging system, exhaust gas
recirculation).

34

-Mode 7:
Read out faults which have still not activated
the
self diagnosis fault warning lamp.

-Mode 8:
This mode is not used in Europe.

-Mode 9:
Display vehicle information
(e.g. ID No., engine code, engine control unit
type, software identification, software
checksum).

Vehicle Diagnostic, Testing and Information System VAS 5051

Using VAS 5051, you can read out the readiness code and perform the individual short trips for the
vehicle systems required to generate the readiness code.

Over and above the functions of the OBD visual display unit, VAS 5051 provides additional adjustment,
diagnosis and fault finding functions. The fault-finding procedure can be optimised by accessing all key
engine data.

Read out readiness code

1st possibility:

- Turn on the ignition.

- Activate "Vehicle self diagnosis" mode.

- Select the engine control unit with address
word "01".

- Select function "15 - Readiness code".

2nd possibility (Generic Scan Tool-Mode)

- Turn on the ignition.

- Activate "Vehicle self diagnosis" mode .

- Select Generic Scan Tool Mode with address
word "33".

- Select Mode 1 "Read out actual engine
operating data".

Perform short trips

Use function "04 – Initiate basic setting to invoke
the individual short trips.
Different procedures apply to the various engine
control unit variants.

231_041

For details of the steps and preconditions for
performing the short trips of the various
individual engine control unit variants, refer to
the relevant Workshop Manuals.

35

Function diagram

Example 1: 1.4-ltr. 4V petrol engine 55 kW/Bosch Motronic ME 7.5.10

J17

+12V

S

+12V

N152

G61

G188 G187 G186

+5V

+12V

J338

+12V

+12V

SSS

N30 N31SN32 N33

J220

36

231_053a

Components

G28 Engine speed sender

G39 Lambda probe (before catalyst)

G40 Hall sender

G42 Intake air temperature sender

G61 Knock sensor I

G62 Coolant temperature sender

G71 Intake manifold pressure sender

G79 Accelerator position sender

G130 Lambda probe after catalyst

G39N80

G130

G185 Accelerator pedal position sender -2-

G186 Throttle valve drive

G187 Throttle valve drive angle sender -1-

G188 Throttle valve drive angle sender -2-

G212 Exhaust gas recirculation potentiometer

J17 Fuel pump relay

J220 Motronic control unit

J338 Throttle valve control unit

+12V

+12V

S

G79

+5V +5V

G185

G28G62 G40 N18 G212 G42 G71

+5V

ABC

J220

Input signal

Output signal

Positive

Earth

Data line

+12V

231_053b

N18 EGR valve

N30 Injector, cylinder 1

N31 Injector, cylinder 2

N32 Injector, cylinder 3

N33 Injector, cylinder 4

N80 Activated charcoal filter system solenoid valve 1

N152 Ignition transformer

SFuse

A Signal to self diagnosis fault warning lamp K83

(in models dating from 2000, this signal is

transferred via the CAN bus)

B Road speed signal from control unit

with display unit in dash panel insert J285

C CAN bus

37

Function diagram

Example 2: 1.4-ltr. 4V petrol engine 55 kW/Magneti Marelli 4LV

+12V

J338

+5V

+12V

N152

G88 G69 V60

+12V

N30 N31 N32 N33

J17

+12V

J537

S

G130G39N80

+12V

38

231_054a

Components

Components

G28 Engine speed sender

G28 Engine speed sender

G39 Lambda probe (before catalyst)

G39 Lambda probe (before catalyst)

G40 Hall sender

G40 Hall sender

G42 Intake air temperature sender

G42 Intake air temperature sender

G61 Knock sensor I

G61 Knock sensor I

G62 Coolant temperature sender

G62 Coolant temperature sender

G69 Throttle valve potentiometer

G69 Throttle valve potentiometer

G71 Intake manifold pressure sender

G71 Intake manifold pressure sender

G79 Accelerator position sender

G79 Accelerator position sender

G88 Throttle valve positioner potentiometer

G130 Lambda probe after catalyst

G212 Exhaust gas recirculation potentiometer

J17 Fuel pump relay

J537 Control unit for 4LV

J338 Throttle valve control unit

G61

+5V +5V

+5V

G79

J537

ABC

Input signal

Output signal

Positive

Earth

Data line

G40G62 G28 G42 G71

N18 EGR valve

N30 Injector, cylinder 1

N31 Injector, cylinder 2

N32 Injector, cylinder 3

N33 Injector, cylinder 4

N80 Activated charcoal filter system solenoid valve 1

N152 Ignition transformer

SFuse

V60 Throttle valve positioner

N18 G212

+12V

231_054b

A Signal to self diagnosis fault warning lamp K83

(in models dating from 2000, this signal is

transferred via the CAN bus)

B Road speed signal from control unit

with display unit in dash panel insert J285

C CAN bus

39

Function diagram

Example 3: 1.6-ltr. petrol engine 74 kW/Siemens Simos 3

J17

+12V

S

+5V

+12V

N152

G188 G187 G186

+12V

J299

J338

+12V

J361

+12V

SS S

N30 N31SN32 N33

N156

40

231_055a

Components

G28 Engine speed sender

G39 Lambda probe (before catalyst)

G40 Hall sender

G61 Knock sensor I

G62 Coolant temperature sender

G70 Air-mass flow meter

G79 Accelerator position sender

G130 Lambda probe after catalyst

G185 Accelerator pedal position sender -2-

V101

G39N80G61

+12V

G186 Throttle valve drive

G187 Throttle valve drive angle sender -1-

G188 Throttle valve drive angle sender -2-

G212 Exhaust gas recirculation potentiometer

J17 Fuel pump relay

J299 Secondary air pump relay

J361 Simos control unit

J338 Throttle valve control unit

+12V

N18 G212

G79 G185

+5V +5V +5V

J361

ABC

In future, lambda
probes by NTK will also
be fitted in combination
with Simos engine
control units.

Input signal

Output signal

Positive

Earth

Data line

G130

+12V

N18 EGR valve

N30 Injector, cylinder 1

N31 Injector, cylinder 2

N32 Injector, cylinder 3

N33 Injector, cylinder 4

N80 Activated charcoal filter system solenoid valve 1

N112 Secondary air inlet valve

N152 Ignition transformer

N156 Intake manifold change-over valve

SFuse

G70N112

G62 G28

V101 Secondary air pump

A Signal to self diagnosis fault warning lamp K83

B Road speed signal from control unit

C CAN bus

+5V

G40

231_055b

(in models dating from 2000, this signal is

transferred via the CAN bus)

with display unit in dash panel insert J285

41

Glossary

Adaption

Adapt to changed conditions.

D2, D3, D4

Exhaust emission standards of the Federal
Republic of Germany
(refer to Self-Study Programme 230)

NEFZ (Neuer Europäischer Fahrzyklus)
New European driving cycle for determining the
exhaust emissions of motor vehicles

kph

120

60

0

195 390 585 780 1180

Electrode

Interface between an electrical circuit and a
liquid or gaseous environment

(e.g. exhaust gas, ambient air)

sec.

IWDS (Integrierter Wellendichtring-Sensor)
Integrated shaft sealing ring sensor

Lambda

(fuel-air ratio, λ)
Factor which describes the air concentration in
the fuel/air mixture.

<1.0=rich mixture

λ

>1.0=lean mixture

λ

=1.0=theoretical optimal

λ

mixing ratio

Theoretically, λ is the air inflow rate to
(theoretical) air demand ratio:
Air inflow rate / air demand = lambda

λ

Lambda control value

The engine control unit calculates the lambda
control value from the lambda probe signals and
engine operating state (e.g. engine speed,
engine load). Based on this value, the fuel/air
mixture is altered until the optimum ratio for the
operating state is achieved.

LSF

Lambda probe flat (step type lambda probe)

42

EOBD

Euro On-Board Diagnostics

EU II, EU III, EU IV

Exhaust emission standard of the European
Union
(refer to Self-Study Programme 230)

Generic Scan Tool

(OBD visual display unit)
It must be possible to read out all emission­related faults which the EOBD has detected via
the diagnosis interface with any OBD visual
display unit.
The use of OBD visual display units for spot
checks is also planned.

LSH

Lambda probe heating (finger probe)

LSU

Lambda probe universal (broadband lambda
probe)

Modulation

To change or adapt the oscillation frequency
of a signal.

Moment of force

The moment of force (better known as"torque")
is the product of an applied force and the
associated leverage.

Pump cell

The pump cell comprises two electrodes
separated by a ceramic material permeable to
oxygen. The oxygen ions O

(negatively

2

charged) are conducted through the ceramic
from the negatively charged electrode (cathode)
to the positively charged electrode (anode). The
result is the so-called "pump effect".

Moment of force = force x leverage

Force

Leverage

Example with piston, connecting rod and crankshaft

Nernst cell

(part the of lambda probe)
The Nernst cell measures the differential
between the oxygen concentrations in the
ambient air and the exhaust gases and
generates a corresponding voltage U. The
Nernst cell comprises two electrodes, one on
the ambient air side and and the other on the
exhaust side.

Readiness code

8-character number code which indicates
whether the OBD diagnoses of the vehicle
systems were performed.

"0" - performed
"1" - not performed

SAE code
Fault code defined by the Society of Automotive
Engineers and binding for all OBD systems.

Waste g a te

(also known as "bypass")
The waste gate passes excess exhaust gases by
the turbocharger drive. This allows the
turbocharger to be deactivated or turbocharger
power output to be reduced.

OBD

On-Board Diagnostics

43

Test your knowledge

1. Until when can buyers register new cars without EOBD if the new cars meet exhaust emission
standard D3?

a) 31.12.1999

b) 01.01.2000

c) 31.12.2000

2. When does self diagnosis fault warning lamp K83 begin to flash?

3. What are the important points to note when replacing a broadband lambda probe (LSU)?

a) The broadband lambda probe and the engine control unit are a system. Therefore, it is also

necessary to replace the engine control unit.

b) If the vehicle has two lambda probes, both probes must be replaced.

c) The broadband lambda probe and the engine control unit are a system and must match

one another.

d) The broadband lambda probe may only be replaced complete with cable and connectors.

4. What is a Generic Scan Tool (OBD visual display unit) used for?

a) The readiness code can be processed with it.

b) Emission-related data, readiness codes, faults, fault conditions and vehicle data can

be read out with it. In addition, fault and readiness codes can be cancelled.

c) Emission-related data, readiness codes, faults, fault conditions and vehicle data can

be read out with it. In addition, fault and readiness codes can be canceled and short trips
can be performed.

44

Notes

45

Notes

4. b

3. c, d

damaged due to misfiring.

2. If the catalyst can be

1. c

Solutions:

46

47

231

For internal use only © VOLKSWAGEN AG, Wolfsburg

All rights reserved. Technical specifications subject to change without notice.

040.2810.50.20 Technical status: 05/00

❀ This paper is produced from

non-chlorine-bleached pulp.