AUDI A4 1995 B5 / 1.G APB Engine Electronic Engine Power Control Checking Workshop Manual

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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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Significance of electronic Engine Power
Control (EPC) warning light in
instrument cluster

"EPC" stands for Electronic Power Control and
refers to the electronic throttle control system
(Drive by wire).

Component location of EPC warning light
The Engine Control Module (ECM) checks after the ignition has been
switched on all important parts of the electronic throttle control system for
functionality.
After the ignition is switched on the ECM turns on the EPC warning light.
Shortly after the engine has been started the EPC warning light goes out
if, no malfunctions regarding the electronic throttle control system are
stored in the ECM and if the activation for the EPC warning light is OK.
If a malfunction is detected in the electronic throttle system while the
engine is running, the ECM will activate the EPC warning lamp. At the
same time a Diagnostic Trouble Code (DTC) is stored in the DTC memory
of the Engine Control Module (ECM).
Checking function of warning light
- Switch ignition on.
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Specified value: The EPC warning light should
light up.
If the EPC warning light does not light up:

- Check wire from Engine Control Module (ECM)
to EPC warning light in instrument cluster as
follows: Cause:
EPC warning light is not activated or does
not light up because of an open circuit. Corrective action:
The EPC warning lamp should light up.
If the EPC warning lamp does not light up:
If the warning lamp and the voltage supply are OK: - Switch ignition off
- Connect VAG1598/31 test box . Do not connect engine control module.
- Bridge sockets 1 and 48 on test box
- Switch ignition on.
- Switch ignition off.
- Check whether lamp is burned out and test voltage supply to lamp wiring
diagram.
- Check for open circuit or short circuit in wiring between engine control module
and EPC warning lamp using wiring diagram. Determine and eliminate
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malfunction.
If there are no malfunctions in the wiring to the EPC warning lamp:
Malfunction cause: Engine control module (ECM) faulty Replace Engine Control Module (ECM)
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If EPC warning lamp remains lit for more than 3
seconds (i.e. continuously) when ignition is on,
proceed with test as follows:

- Start engine and allow it to run at idling speed.

Specified value: EPC warning lamp should go
out.
If the EPC warning lamp does not go out:

- Check DTC memory of Engine Control Module
(ECM).
If no DTCs are stored: Cause:
EPC warning light is activated via
short circuit to Ground (GND). Corrective action:
If the specification is not reached: - Switch ignition off
- Connect VAG1598/31 test box . Do not connect engine control module.
- Measure resistance between vehicle Ground and socket 48 on test box. Specified
value: infinity (because the wire should not have any direct Ground connection)
- Determine and eliminate short circuit to Ground in wiring between engine control
module and EPC warning lamp using wiring diagram.
If there are no malfunctions in the wiring to the EPC warning lamp:
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Malfunction cause: Engine control module (ECM) faulty Replace Engine Control Module (ECM)
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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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The potentiometers cannot be adjusted
mechanically. Settings are made using the
"Basic Setting" function (function 04) with
VAG1551 scan tool or VAG1552.
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