air condition AUDI A6 ALLROAD 1999 C5 / 2.G Pneumatic Suspension System

6
Description of the system
• The 4 level stages can be controlled
manually or automatically within defined
limits (see page 8 onwards).
• Individual automatic functions or the
entire system can be switched off via the
control system.
• LEDs in the operating unit indicate the
operating status and the control
procedures to the driver.
• Pressure accumulator system for
maximum comfort. The newly developed fully-supporting air
suspension system on all four wheels was
designed specifically for the allroad quattro .
As well as the advantages of air suspension-
based self-levelling, as described for the A6
(see SSP 242), this system offers additional
benefits.
• The 4-level air suspension is a
sophisticated electronically controlled air
suspension system at both axles. The
system enables variation of the floor level
by 66 mm and offers four defined height
levels with between 142 and 208 mm
ground clearance.
• Depending on the driving conditions and
requirements you can select greater
ground clearance or a low vehicle centre
of gravity and a good c
w

value.
• The 4-level air suspension keeps the pre-
set vehicle level constant, regardless of
load and weight distribution.
242_067

7
Operation and display
Operation
The self-levelling control unit E281 is used to
control the 4-level air suspension and the
display/monitor the system status.
Certain level changes occur automatically
during normal driving (see Control strategy).
Within defined conditions (see Control
strategy) the driver can use the “raise” or
“lower” buttons to select an appropriate level
at any time. Pressing the “raise” button once selects the
next highest level. By pressing the button
repeatedly, it is possible to change, e.g.
directly from low level to high level 1. High
level 2 cannot be selected until high level 1
has already been set.
Changing to a lower level is performed in the
same manner as described above using the
“lower” button. By pressing several times (x3)
it is possible to shift directly from high level 2
to the low level.
Operating unit for self-levelling E281
241_062
It is possible to switch to a higher level
only when the engine is running or
when sufficient pressure is present in
the pressure accumulator.
It is possible to change to a lower level even
when the engine is switched off.

30
The driving speed signal …
... is a square-wave signal produced by the
dash panel, the frequency of which is
changed in accordance with the vehicle
speed.
... is required in the evaluation of the driving
condition (stationary/driving mode) and
thereby for selection of the control criteria
(see “Control concept”).
The interface for the driving speed signal is
redundant, as the information regarding
speed is also transmitted by the CAN bus.
K wire
Communication for self-diagnosis between
control unit J197 and the diagnostic tester
takes place via the familiar K wire by means of
conventional data messages.
The self-diagnosis K wire must not be
confused with the K wire connecting
operating unit E281 to control unit J197.
Power supply to the headlamp range control
system
In the case of 4-level air suspension in the
allroad quattro, the headlamp range control
system voltage is supplied by the air
suspension control unit J197. Further
information can be found under Control unit
J197 on page 34.
Additional interfaces
The door contact signal …
... is an earth signal from the control unit for
central locking. It indicates that the door or
boot lid/tailgate is open.
... serves as a “wake-up pulse” for transfer
from sleep mode to run-on mode (see
“Control concepts”).
Terminal 50 signal...
... signals actuation of the starter and is used
to switch off the compressor during start-up.
If a low position is detected following a wake-
up pulse, the compressor is activated
immediately in order to allow the vehicle to
drive off as quickly as possible.
The compressor is switched off during start-
up in order to save battery power and ensure
starting power.
The vehicle locking signal …
... is used as information for parking level
control
... is an earth pulse coming from the control
unit for central locking J429
... is not detected by the self-diagnosis.
Parking level control is not performed if this
signal fails.
Interfaces
The vehicle locking signal is not
required for vehicles without parking
level control (see pages from 10
onwards and 34 onwards).