2003 AUDI A8 ESP

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Vehicle electrical system
A major factor in terms of vehicle reliability is
one which is never even seen: the electrical
system.
Use is made for the Audi A8 ´03 of a customer-
specific one-piece modular wiring harness.
"One-piece" means that power is supplied for
all essential electrical functions from a single
continuous wiring harness. The only isolating
points are at the doors, roof module and
engine.
"Customer-specific" means that each wiring
harness is designed to serve exactly the
equipment ordered by the customer. The
wiring harness is subdivided into individual
logic modules, each of which is responsible
for a clearly defined range of functions.
SSP282_038
Design and operation of the optical fibre
are described in SSP 286 – New data bus
systems. A plastic optical fibre is fitted for the
transmission of optical communication and
infotainment signals.
Its advantages as compared to a copper
conductor are its insusceptibility to
electromagnetic interference, a high
transmission capacity and less weight.
To achieve greater headroom, the wiring
harness to the roof module has been
extended to include the flexible flat cable
(FFC). This represents a new method of
solving the wiring problem in extremely
confined spaces (max. 2 mm between
headliner and body outer skin).

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Electrical System
Convenience and security
electronics
"Advanced Key" entry and start
authorisation system
"Advanced Key" can be taken to mean an
"advanced locking and security system".
It takes the form of a non-contacting key
recognition system. With the "Advanced Key"
package, the "Vehicle unlocking" and "Vehicle
locking" functions by way of a mechanical or
remote control key are supplemented by the non-
contacting functions "Vehicle unlocking" and
"Vehicle locking".
Functions
Advanced Key "unlocking"
The key owner enters the key detection zone next
to the vehicle (less than 1.5 m from door handle)
and reaches into the recessed handle moulding.
aerial.
The key responds by way of radio waves and the
vehicle is unlocked if authorised.
Advanced Key "starting"
The driver presses the start button, which again
initiates a key scan via the passenger-
compartment aerials near the selector lever, at the
rear centre vents and at the rear centre armrest.
The remote control key provides confirmation,
with the result that the ignition is switched on on
depressing the first stage of the start button and
the engine started on depressing the second
stage. The engine is switched off with the STOP
button.
Advanced Key "locking"
If the vehicle is to be locked from the outside, it is
sufficient to press the locking button in one of the
door handles. Actuation of the locking button
triggers a key scan via the door handle aerial and
the vehicle is locked on confirmation of the remote
control key.In addition, the driver can start the engine
with the START/STOP button (START/STOP
function) without inserting the ignition key
in the electronic ignition lock.
SSP282_093
SSP282_094
SSP282_095
Design and operation are described in
SSP 287 – Audi A8 ´03 Electrical
Components.
A proximity sensor starts a key scan by way of an

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Electrical System
The headlight in the Audi A8 ´03 combines both
design elements and innovative technology.
Headlight versions:
– Basic halogen version H7
Dynamic headlight range control is not
necessary with halogen headlights. The air
suspension provides compensation for static
load statuses and a thumbwheel is therefore
also not required.
– Bi-xenon version
– Bi-xenon version with integrated adaptive
light function
The headlight range control unit J431 is
responsible for providing static and dynamic
compensation for vehicle tilting as well as
actuation of the static adaptive light
function. The sensor signals of the 4-level air
suspension system are picked off by the
drive system CAN for control purposes. A
distinction is made between the two
gas-discharge lamp versions by way of
appropriate encoding (1 or 2) at the
headlight range control unit.
Lighting system
Front lights
SSP282_056
HPV stands for high-performance bulbs,
which are extremely compact and have a far
longer service life. They have a 25 % lower
power input than conventional bulbs. Such
bulbs cannot be replaced by customers.
Both bi-xenon versions feature an ellipsoid
module with a moving screen to achieve both
dipped beam and main beam with xenon light.
The automatic dynamic headlight range control
represents a more advanced version of the
standard automatic control system. It provides
headlight tilt compensation not only for various
load statuses but also as a dynamic function
reacting to differences in running gear
inclination caused by acceleration and
deceleration.
Dipped beam/main beam
(Bi-Xenon/D2S - gas-discharge lamp)Turn signal indicator
(2 x 16 W HPV bulb - yellow) Parking light
(W5W/5 W bulb)Adaptive light
(H8/35 W bulb)
Additional main beam
Headlight flasher
(H7/55 W bulb)Reflector
for adaptive light

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3
36
Auto
21,5° C
63
3
The current air conditioner settings are stored
automatically and assigned to the
appropriate remote control key. On vehicles
with Audi one-touch memory (optional), the
current setting is also assigned to the
corresponding fingerprint. Air conditioning system control via MMI
All air conditioning system set values and
basic settings (setup) can be displayed by
way of the MMI. This applies both to the
Climatronic control unit button functions and
to setup.
If the air conditioning system is activated
with the MMI switched on, the air conditioner
function settings can be called up and altered
by way of the multimedia control panel. The
functions indicated in the corners of the
displayed mask are activated using the
softkeys.
Basic setting (setup)
The basic air conditioner settings can only be
altered when the MMI is active. This involves
pressing the SETUP button on the Climatronic
control unit.
The following functions can be selected:
– ECON ON/OFF
– Automatic air recirculation active/inactive
– Synchronisation active/inactive
– Centre vent (temperature-adjustable)
settings between - 3 and + 3
– Auxiliary heater active/inactive
– Auxiliary ventilation active/inactive
– Auxiliary heater/ventilation operating time
15 min./30 min./45 min./60 min.
– Auxiliary heater/ventilation timer status for
timers T1, T2, T3 ON/OFF
– Solar mode active/inactive (solar cells
C20)
– Rear control ON/OFF
The desired settings can be called up and
altered with the driver's/front passenger's
control knob on the Climatronic control unit.
SSP282_112
SSP282_113
low high
Econ
Distribution Seat ventilation
Blower Seat heatingAC - driver
Blower Seat heatingAC setup
Distribution Seat ventilation
Off
Autom. air recirculationOff
Synchron.Off
Centre vent

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Humidity sender G355
Heating/Air Conditioner
At low ambient temperatures, when the
windscreen is extremely cold, the top third is
particularly susceptible to fogging.
To cover this area, the humidity sender G355
is fitted in front of the base of the rear view
mirror.
The sender is designed to detect the
following:
– Humidity level
– Sender ambient temperature and
– Windscreen temperature
All three functions are combined in the
sender housing.
The humidity sender is intended for all
equipment versions.The sender data enable the air conditioning
system to detect potential misting of the
windscreen in good time.
Before water vapour from the air in the
passenger compartment can form on the
windows, the output of the air conditioner
compressor and the blower speed are
automatically increased and the defrost flap
is opened further. Dry air is then routed from
the open defrost vents to the windscreen and
side windows via the evaporator and heat
exchangers.
Measurement of humidity level and
corresponding temperature
Physical principles
Humidity measurement involves determining
the water vapour content of the passenger
compartment air. The capacity of air to
absorb water vapour is governed by the air
temperature. It is thus necessary to
determine not only the humidity level but also
the corresponding air temperature in the
measurement area.The warmer the air, the more water vapour it
can absorb. Water starts to condense if this
water-vapour enriched air cools down again.
This results in fine droplets forming on the
windscreen.
SSP282_104

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The buttons for the seat heating and
ventilation options are integrated into the
front and rear control and display units
(refer to Page 74). Climate-controlled seats with heating and
ventilation function
The Audi A8 ´03 can be fitted with front and
rear climate-controlled seats as optional
equipment. These seats offer a combination
of seat heating and seat ventilation and can
be regulated individually for each occupant.
Heating/Air Conditioner
The corresponding feedback LED lights after
pushbutton activation of seat heating/seat
ventilation. The selected seat heating/seat
ventilation stage can be called up in the
display segment of the Climatronic control
unit J255 and in the MMI (Multimedia
Interface) climate control menu. Once seat
heating/seat ventilation has been activated, it
remains active even after switching off the air
conditioner by means of the ON/OFF button.The use of seat ventilation leads to lower
occupant skin temperatures. Automatic
additional seat heating operation controlled
as a function of temperature cancels the
cooling effect and the air flow is warmed.
The ventilation function promotes pleasant
conditions in the occupant's back and seat
area and eliminates sweating more quickly.
Under normal circumstances, the seat
ventilation function is deactivated
automatically after approx. 30 minutes.
SSP282_107 Seat heating
button
Seat ventilation
button

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4.2 Auxiliary heating sequence
The level of fuel in the tank is
interrogated. If the fuel tank is "empty",
the auxiliary heating function is not
permitted and the auxiliary heater symbol
in the dash panel insert goes out. "Empty"
roughly corresponds to the red display
zone. The energy management control
unit J644 checks whether there is
sufficient energy to accept auxiliary
heating. If this is the case, the auxiliary
heater is switched on in the various
operating modes depending on the
characteristic temperature curve and the
fresh-air blower is actuated.
If the auxiliary heating temperature
reaches a level of 30 °C, the fresh-air
blower is activated and the coolant
shutoff valve N279 pulsed in line with the
characteristic curve.
The auxiliary heater is switched off
automatically on completion of the operating
time transmitted by the MMI system to the
Climatronic control unit or it can be switched
off using the remote control OFF button.
Auxiliary heater circulation pump control
To speed up heating of the passenger
compartment and to achieve a better "heat
yield" in the air conditioner unit heat
exchanger, the circulation pump V55 and
coolant shutoff valve N279 are pulsed as a
function of water temperature and the
heating circuit flow rate is thus reduced.
An electric circulation pump is used for the
auxiliary heater. It is not possible to reduce
the supply voltage in the auxiliary heater
control unit and the circulation pump is thus
actuated at specific intervals to decrease its
output.
Additional control curve for "auxiliary heater"
and "additional heater"
When the engine is on, the auxiliary heater
and engine temperatures are constantly
compared. A switch to the large coolant
circuit is made as soon as the engine
temperature exceeds the auxiliary heater
temperature.
Activation of auxiliary heater circulation
pump with engine on
(pulsed operation of circulation pump)
In order to be able to ensure a sufficient flow
of water through the heat exchanger, the
auxiliary heater circulation pump must
additionally be switched on, as is the case for
instance with the 12-cylinder engine.If the engine is switched off again and not
all additional heater criteria (temperature,
time) are satisfied, the auxiliary heater
remains in operation for any residual
operating time before being deactivated.
This function can be encoded.