2000 AUDI A4 sensor

24-139


Electronic Engine Power
Control (EPC), checking

Function of Engine Power Control (EPC)

With the electronic throttle, the throttle valve is
not operated by a cable connected to the
accelerator pedal. There is no mechanical link
between the accelerator pedal and the throttle
valve.
The throttle valve is actuated by a servomotor
(throttle valve positioner) in the throttle valve
control module over the full range of engine
speeds and load conditions.
The throttle valve positioner actuates the throttle
valve according to the commands it receives
from the Engine Control Module (ECM).
The position of the accelerator pedal is
communicated to the Engine Control Module
(ECM) by two accelerator position sensors
(variable resistors, both installed in a single
housing) which are connected to the accelerator
pedal.
The accelerator pedal position (as determined by
the driver) is one of the main input values for the
Engine Control Module (ECM).
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With the engine is not running and the ignition
switched on, the ECM operates the throttle valve
positioner in exact accordance with the signals
from the accelerator position sensors. For
example, when the accelerator pedal is pressed
down half way, the throttle valve positioner opens
the throttle valve by an equivalent amount, i.e.
about half way.
When the engine is running (i.e. under load) the
ECM can open and close the throttle valve freely,
independently of the signals being sent by the
accelerator position sensors.
For example, the throttle valve might already be
fully open even though the accelerator pedal is
only pressed down half way. This has the
advantage of preventing throttling losses at the
throttle valve.
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Under certain engine load conditions there is
also a significant reduction in harmful emissions
and noticeably improved fuel consumption.
The Engine Control Module (ECM) can provide
the optimum combination of throttle valve
opening and charge pressure in order to create
the required torque.
The electronic throttle is not simply a
combination of two or three components, but
rather a complete system comprising all the
elements that together determine the position of
the throttle valve and also control and monitor it.
For example, the Accelerator Pedal Position
Sensor, Throttle Valve Control Module, EPC
warning lamp, Engine Control Module (ECM)
etc.
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Throttle Valve Control Module -J338,
checking

The throttle valve control module housing
contains the following components:

CAUTION!

The housing should NOT be opened.

Throttle drive -G186 (power accelerator
actuation) (This is an electric motor activated by
the engine control module. The motor opens
the throttle valve by applying force to overcome
the spring pressure.)
Angle sensor -1- for throttle drive (power
accelerator actuation) -G187
Angle sensor -2- for throttle drive (power
accelerator actuation) -G188

Notes:
The angle sensors are in the form of
potentiometers (variable resistors). Each sends
its own separate signal to inform the engine
control module of the position of the throttle
valve (i.e. one of the signals is redundant).
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Throttle valve control module,
adaptation

The adaptation process enables the Engine
Control Module (ECM) to learn the different
positions of the throttle valve with the ignition
switched on and the engine not running. These
positions are stored in the control module. The
feedback signal indicating the position of the
throttle valve comes from the two angle sensors
for throttle valve drive.
If the Throttle Valve Control Module -J338 or the
ECM is removed and installed or replaced, or if
the voltage (power) supply to the ECM is
interrupted, an adaptation must be carried out.
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The learning process (adaptation process) is
carried out:

By selecting "Basic Setting" (function 04),
Display Group 060 with the ignition switched
on.
Automatically if the ignition is switched on for at
least 6 seconds without operating the starter or
depressing the accelerator, and if the Engine
Control Module (ECM) registers a "learning
requirement." (In this case, however, there is no
way of knowing whether the adaptation process
was successful or not.) The engine control
module will register a learning requirement if
the previously stored voltage readings from the
angle sensors do not correspond (within a
certain tolerance range) to the new voltage
readings.

Note:
The engine will not start during automatic
adaptation.
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24-150
When the -Q- button is pressed the throttle valve
positioner will be switched mechanically.
In this condition the throttle valve is pulled into an
"emergency running" or default position by a
mechanical spring in the throttle valve control
module. The values supplied by the two angle
sensors for this emergency running position are
stored in the Engine Control Module (ECM).
The throttle valve is then opened by a
predetermined amount. As soon as it reaches
this position the current supply to the throttle
valve positioner is again disconnected. The
spring should then close the throttle valve
mechanically to the previously learned default
position within a specified period of time (spring
test).
The throttle valve positioner then closes the
throttle valve and the values supplied by the
angle sensors in the throttle valve control module
are stored in the Engine Control Module (ECM).
If the ECM disconnects the current supply to the
throttle valve positioner while the vehicle is being
driven, the result will be an increase in idling
speed with fluctuating engine RPM (hunting) and
very slow throttle response.
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- Check specification for throttle valve control
module (display fields 4).

Display fields

1 2 3 4
Display Group 060: Adaptation of throttle valve control module with ignition on
Display xx % xx %
---
---
Indicates Throttle
valve angle
(angle
sensor 1) Throttle
valve angle
(angle
sensor 2) Learning stage counter
Adaptation status
Work
Range min.: 0 %
max.: 100
% min.: 0 %
max.: 100
% 0 to 8
ADP. runs
ADP. O.K.
ADP. ERROR
Specified
value 3 - 20 % 80 - 97 %
8
ADP. OK
Note
Learning stage counter must run from 0 to 8
during adaptation process (some digits may
also skip). If specification is not met:
Notes Page 24
-152
.
Note:

It is not important how the learning stage counter reacts during adaptation, rather the specification "ADP" is reached after
the adaptation in display field 4.
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11/22/2002 htt
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play?action=Goto&t
yp
e=re
pair&id=AUDI.B5.FU04.24.4