Electronic Power Control
Design and Function
Self-Study Programme 210
Service.
2
Please always refer to the relevant Service Literature
for all inspection, adjustment and repair instructions.
Service literature.
The Self-Study Programme
is not a Workshop Manual.
New Important
Note
With the Electronic Power Control system, the
throttle valve is actuated only by an electric
motor.
This eliminates the need for a Bowden cable
between the accelerator pedal and the throttle
valve.
It means that the driver input is relayed to the
engine control unit via the accelerator pedal.
The engine control unit then sends a correspond-
ing command to the throttle valve positioner.
By positioning the throttle valve, the engine con-
trol unit can regulate engine torque even if the
driver has not depressed the accelerator pedal.
The result is better co-ordination between and
within the engine management systems.
We will now demonstrate that the Electronic Power Control is more than just a substitute for the Bowden
accelerator cable.
3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Throttle valve positioning . . . . . . . . . . . . . . . . . . . . . . . . 4
System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Control process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
System design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
What happens and when? . . . . . . . . . . . . . . . . . . . . . . 8
System components . . . . . . . . . . . . . . . . . . . . . . . . . . 10
System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
The engine control unit . . . . . . . . . . . . . . . . . . . . . . . . . 11
The accelerator pedal module . . . . . . . . . . . . . . . . . . 14
The throttle valve control unit . . . . . . . . . . . . . . . . . . . 16
The fault indicator lamp . . . . . . . . . . . . . . . . . . . . . . . . 22
Auxiliary signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Function diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Self-diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Test your knowledge . . . . . . . . . . . . . . . . . . . . . . . . . 30
Table of contents
4
Throttle valve positioning
Mechanical throttle valve positioning system
With this system, the driver depresses the accel-
erator pedal and thus positions the throttle valve
mechanically by means of a Bowden cable.
When the driver depresses the accelerator
pedal, the engine management system cannot
control the position of the throttle valve.
To regulate engine torque, the engine manage-
ment system must refer to other controlled
variables such as ignition timing and injection
timing.
Throttle valve positioning by an electric motor
drive is only possible in the idling speed range
and in combination with the Volkswagen cruise
control system.
Electric throttle valve positioning system
With this system, the throttle valve is positioned
by an electric motor across the full adjustment
range.
The driver depresses the accelerator pedal
according to the engine power required. Senders
register the accelerator pedal position and relay
this information to the engine control unit. The
engine control unit now sends a signal corre-
sponding to the driver input to the throttle valve
positioner which in turn sets the throttle valve to
the appropriate angle.
If the engine torque has to be adjusted for rea-
sons of safety or fuel consumption, however, the
engine control unit can adjust the position of the
throttle valve independent of the accelerator
pedal position.
The advantage of this is that the control unit
defines the position of the throttle valve
according to the various individual requirements
(driver input, exhaust emissions, fuel consump-
tion and safety).
Introduction
210_007210_008
5
System description
Engine torque control with
mechanical throttle valve positioning
The various torque requirements are signalled
individually to the engine control unit and then
processed.
The torque demands cannot be matched opti-
mally because the engine control unit cannot
access the mechanically adjustable throttle valve
directly.
Engine torque control with
electric throttle valve positioning
This system permits torque-oriented
engine management.
What does this mean?
First, the engine control unit gathers all the
internal and external torque demands. Then it
calculates the necessary control actions.
This system is more precise and efficient than the
previous system.
Internal torque demands include:
- Start
- Catalytic converter heating
- Idle speed control
- Power limitation
- Speed limiting device
- Lambda control
External torque demands originate from:
- the automatic gearbox (shift point)
- the brake system (Traction Control System,
engine braking control)
- the air conditioning system
(air conditioner compressor ON/OFF) and
- the cruise control system
Internal
requirements
External
requirements
Optimal
efficiency
210_009
The "tools“ which the engine management system uses to influence the engine torque are:
throttle valve, charge pressure, injection timing, cylinder suppression and ignition advance angle.
Engine
control unit
6
Introduction
Control process
With the first line of approach, the system acti-
vates the controlled variables that affect charge.
These variables are also known as controlled
variables for long-term torque demand.
They are:
- throttle valve angle and
- charge pressure (turbocharged engines).
With the second line of approach, the system
changes the controlled variables that affect
short-term torque independent of charge.
They are:
- ignition point,
- injection time and
- cylinder suppression.
Specific
torque
Actual
torqueAir flow rate
1st line of approach 2nd line of approach
Ignition,
fuel injection
Engine control unit
210_010
The engine management system generates a
specific torque according to the external and
internal torque demands.
Actual torque is calculated from the following
factors: engine speed, load signal and ignition
advance angle.
The system pursues two lines of approach simultaneously.
The engine control unit initially compares the
actual torque and the specified torque. If these
two values differ from one another, the system
determines the corrective action necessary to
make these values match.
On the following pages, we will show you how the electric throttle valve positioning function
works.
7
System design
The accelerator pedal module
determines the current accelerator pedal position
with its senders and sends a corresponding
signal to the engine control unit.
The engine control unit
calculates from this signal how much engine
power is required by the driver and converts this
information into an engine torque value. For this
purpose, the engine control unit activates the
throttle valve drive in order to open or close the
throttle valve further. When activating the throttle
valve drive, the engine control unit makes allow-
ance for additional engine torque demand
factors such as air-conditioning.
In addition, it monitors the
"Electronic Power Control” function.
The throttle valve control unit
is responsible for providing the required air mass
flow.
The throttle valve drive actuates the throttle valve
in accordance with the instructions issued by the
engine control unit.
The throttle valve angle senders supply the
engine control unit with feedback on the position
of the throttle valve.
The fault indicator lamp for Electronic Power
Control
indicates to the driver that there is a fault in the
Electronic Power Control system.
Electronic Power Control comprises:
- the accelerator pedal module together with the accelerator position senders,
- the engine control unit,
- the throttle valve control unit, and
- the fault indicator lamp for Electronic Power Control.
Throttle valve control unit
Accelerator pedal module
Fault indicator lamp
Auxiliary signals
210_011
8
Introduction
What happens and when?
In idling mode
The engine control unit can recognise from the
signal voltages of the accelerator position sender
that the accelerator pedal is not depressed.
The idle speed control process now commences.
The digital idling stabilisation function also supports the idle speed control process.
Engine
control unit
Accelerator pedal module
Angle sender for
throttle valve drive
Accelerator position
sender
Throttle valve
control unit
The two angle senders for throttle valve drive sig-
nal the current position of the throttle valve to the
engine control unit.
They are located in the throttle valve control unit.
Throttle valve
drive
The engine control unit activates the throttle
valve drive and positions the throttle valve by
means of an electric motor.
The throttle valve is opened or closed further
depending on the extent to which the actual
idling speed deviates from the specified idling
speed.
210_019
210_060
210_061
9
Pressing the accelerator pedal
The engine control unit can recognise from the
signal voltages of the accelerator position sender
the extent to which the accelerator pedal is
depressed. Using this information, the engine
control unit calculates the driver input and posi-
tions the throttle valve by actuating the throttle
valve drive by means of an electric motor.
The engine control unit also controls the ignition
timing, the injection timing and, if necessary, the
charge pressure.
The engine control unit makes allowance for
additional engine torque demand factors when
calculating the necessary throttle valve position.
These include:
- the speed limiting device
- the cruise control system
- the Traction Control System (TCS) and
- the engine braking control (EBC)
When engine torque is required, the throttle
valve can be adjusted even if the driver has not
changed the accelerator pedal position.
The two angle senders for throttle valve drive
determine the throttle valve position and send a
corresponding signal to the engine control unit
210_021
210_062
210_063
TC Air EBC
10
System overview
System components
Sensors Actuators
Brake light switch F
and
brake pedal switch F47
Clutch pedal switch F36
Accelerator pedal module with
accelerator pedal position
sender -1- G79 and
accelerator pedal position
sender -2- G185
Throttle valve control unit
J338
angle sender 1
for throttle valve drive G187
and
angle sender 2
for throttle valve drive G188
Fault indicator lamp for
electric throttle control
K132
(Electronic Power Control)
Throttle valve drive G186
Engine control unit J...
Diagnostic connection
Throttle valve control unit J338
with
210_037
Auxiliary signals from:
- automatic gearbox,
- brake system,
- air conditioning system,
- cruise control system,
and others
The system components
may be different to those
shown in this overview
depending on vehicle
equipment specification.
11
Engine control unit J...
Design
Put in simple terms, the engine control unit com-
prises two processing units:
the function processor and
the watchdog processor.
- The function processor
receives the signals from the sensors,
processes them and then activates the
actuators.
The function processor also checks the
watchdog processor.
- The watchdog processor
serves only to check the function processor.
Function processor Watchdog processor
210_012
210_031
Its tasks in the Electronic Power Control:
The EPC calculates from the input signal supplied
by the accelerator position sender how much
engine power the driver requires and converts
this information into an engine torque by means
of the actuators.
The engine control unit makes allowance for
additional functions of the engine management
system (e.g. engine speed limitation, road speed
limitation and power limitation) and other vehicle
systems (e.g. the brake system or the automatic
gearbox).
The engine control unit also monitors the
"Electronic Power Control“ system in order to
prevent malfunctions occurring.
12
System components
Monitoring function
The watchdog processor continuously monitors
the functions of the function processor.
At the same time, it checks the output signals of
the function processor against its own calcula-
tions. The function processor and the watchdog
processor check each other by means of a query
& answer function.
If faults are found, both processors can influence
the throttle valve control unit, the ignition and the
injection independently from one another in
order to shut down the engine.
checks
output signals
calculates
corrective
actions
A
ct
ua
to
rs
Se
ns
or
s Output
signal
Output
signal
Function processor
Watchdog processor
The watchdog processor checks the function processor with the
query & answer function.
Error counter
qu
er
ie
s a
ns
w
er
s
The watchdog processor queries the function
processor with regard to, say, engine speed or
ignition advance angle. Then it checks whether
the answer is correct. If a wrong answer is given,
the error counter of the watchdog processor is
incremented.
The engine is shut down after five wrong
answers.
Five wrong answers can be detected in less than
a half second.
210_014
210_013
A
ct
ua
to
rs
Se
ns
or
s
Function processor
Watchdog processor
Engine
is shut down
if necessary
13
The function processor checks the watchdog processor
The function processor gives no answer or gives an answer at the wrong point in time
To monitor the watchdog processor, the function
processor deliberately gives a wrong answer.
If the watchdog processor recognises the wrong
answer, this error is registered in the error coun-
ter and returned to the function processor. If the
watchdog processor does not recognise the
wrong answer, the error counter of the function
processor is incremented.
The engine is shut down after the watchdog
counter fails to recognise five wrong answers.
In this case, the engine is shut down immediately.
qu
er
ie
s
gi
ve
s
w
ro
ng
a
ns
w
er
Function processor
Watchdog processor
se
nd
s
co
un
t
Function processor
Watchdog processor
no
answer
210_015
210_016
qu
er
ie
s
A
ct
ua
to
rs
Se
ns
or
s
A
ct
ua
to
rs
Se
ns
or
s
14
System components
The accelerator pedal module
comprises
- the accelerator pedal,
- accelerator pedal position sender -1- G79 and
- accelerator pedal position sender -2- G185
Two senders are used to ensure maximum safety.
This system configuration is also known as a
"redundant system".
Redundant literally means "superfluous". In tech-
nical terms, there is redundancy when, for
instance, an item of information occurs more
often than is required for system operation.
Open housing on accelerator
pedal module showing senders
G79 and G185.
Signal utilisation
The engine control unit is able to recognise the
current position of the accelerator pedal from the
signals supplied by the two accelerator position
senders.
The two senders are sliding contact potentiome-
ters and are mounted on a common shaft.
The resistances of the sliding contact potentiome-
ters and the voltages transmitted to the engine
control unit vary with each change in the
accelerator pedal position.
The signal voltages are indicative of
kick-down and idling speed.
The idling speed switch F60 in the
throttle valve control unit is no longer
required.
Sliding contact
path
Sender
Accelerator pedal position
sender -2-
Accelerator pedal position
sender -1-
210_039
210_064
210_002A
15
Electrical circuit
A voltage of 5 volts is present at both sliding con-
tact potentiometers.
For safety reasons, each sensor has its own
voltage supply (red), its own earth connection
(brown) and its own signal wire (green).
A series-type resistor is fitted in sender G185.
As a result, two different characteristics are
obtained for the two senders. This is a prerequi-
site for the safety and test functions.
The signal from the sender is read out in percent on the associated measured value block.
Hence, 100% = 5 volts.
G79 G185
R
[Ω]
G79
s[m]
G185
The following happens when both senders fail:
An entry is made in the fault memory and the
fault indicator lamp for Electronic Power Control
is activated.
- The engine runs at a higher idling speed
(max. 1500 rpm) only and no longer responds
to the accelerator.
Effects of signal failure
The following happens when one sender fails:
- An entry is made in the fault memory and the
fault indicator lamp for electrical throttle
control is activated.
- The system initially activates the idling mode.
If the second sender is found to be in the
idling speed position within a defined test
period, vehicle operation is resumed.
- If full throttle is desired, the engine speed is
increased slowly.
- The idling speed is also registered via the
brake light switch F or
brake pedal switch F47.
- The convenience functions,
e.g. cruise control system or
engine braking moment control, are
deactivated.
210_046
210_052
Simultaneous failure of both senders
may not be identified properly depend-
ing on the engine management system.
- The fault indicator lamp is not
activated.
- The engine runs at a higher
idling speed and no longer responds
to the accelerator.
16
System components
The throttle valve control unit J338
is located on the intake manifold. It ensures that the engine is provided with the required air flow.
Design
It comprises
- the throttle body,
- the throttle valve,
- throttle valve drive G186,
Throttle body
Throttle valve drive
Housing cover with integrated electronics
Gear wheel with spring return
systemThrottle valve
Do not open or repair the throttle valve control unit.
The basic setting procedure must be performed after replacing the throttle valve control unit.
- angle sender 1 for
throttle valve drive G187 and
- angle sender 2 for
throttle valve drive G188.
Angle senders 1+2 for
throttle valve drive
210_006
17
Function
To open or close the throttle valve, the engine
control unit activates the electric motor for throt-
tle valve drive.
The two angle senders provide the engine control
unit with feedback on the current position of the
throttle valve.
For safety reasons, two senders are used.
Electrical circuit
Both angle senders have a common
voltage supply (red) and earth wire (brown).
Each of the two senders has its own
signal wire (green).
The throttle valve drive (blue) is activated
depending on the direction of movement.
Drive
Throttle valve
Angle senders 1+2 for
throttle valve drive
J338
G187 G188
G186
Engine
control unit
210_041
210_051
18
System components
Throttle valve drive G186
The throttle valve drive is an electric motor and is
activated by the engine control unit.
The throttle valve drive operates the throttle valve
by means of a small gear.
The throttle valve can be positioned in infinitely
variable steps between the idling position and
the full-throttle position.
Throttle valve position
- The lower mechanical stop
In this position, the throttle valve is closed. It is
required for the basic adjustment of the
throttle valve control unit.
- The lower electrical stop
is defined in the engine control unit and is
located just above the lower mechanical stop.
During operation, the throttle valve is closed
no further than the lower electrical stop. This
prevents the throttle valve from intruding into
the housing.
Throttle valve drive as shown at the housing cover of the
throttle valve control unit.
Throttle valve drive
Gear
Throttle valve
Return spring
Throttle valve
control unit housing
210_028
210_065
Engine control unit
210_023
19
-