height 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

23
Vehicle level senders G76,
G77, G78, G289 (level
sensors)
The level sensors are so-called angle sensors.
With the aid of the connecting link kinematics
unit, the height changes of the vehicle body
are converted into angle changes.
The angle sensor used in the Audi allroad
quattro is a contact-free sensor which
operates according to the induction principle.
A special feature of the level sensor used is
that it produces two different output signals
proportional to the angle. This allows it to be
used for both 4-level suspension and for
headlamp range control (see pin-assignment
table).
243_031
243_032
One signal output provides a voltage
proportional to the angle (for headlamp range
control) and a second signal output provides
and PWM signal proportional to the angle (for
4-level air suspension).
Level sensor on the front axle
Level sensor installation position
The 4 level sensors are identical in
design, only the brackets and
connecting link kinematics unit vary
according to the side and axle.
The sender arm deflection and thus the
output signal are opposite on the right
and left sides.
For instance, the output during
compression increases on one side and
decreases on the other.

35
Level change process:
Raising - rear axle first, then front axle
Lowering - front axle first, then rear axle
Modes
Height mode/driving mode
Reaction times upon level deviation
Control characteristics during level change
Level change is basically performed axle by
axle, whereby level differences between the
left and right sides are compensated (e.g. if
loaded on one side).Driving speed Reaction time
<5 km/h
Height modeapprox. 5 seconds
approx. 1 second at
extremely low level
>10 km/h
Driving modeapprox. 50 seconds or
15 minutes
depending on the level
deviation
Run-on mode/run-up mode
The run-on mode enables the compensation
of level deviations after the vehicle has been
parked (e.g. caused by passengers leaving the
vehicle or unloading the vehicle) and before
driving off (e.g. caused by intense cooling,
leakage or loading).
In this mode, delay times before commencing
a journey are kept to a minimum.After “Ignition OFF”, the control unit is in the
so-called run-on mode. The control unit
remains active for a maximum of 15 minutes
(via terminal 30) until it goes into sleep mode.
Due to the limited energy available when the
engine is switched off, control limits are
extended and controls are limited in both
number and duration.

39
Basic system setting
The basic system setting of the reference
level in the 4-level air suspension system is
performed by inputting body-level measured
values at normal level.
The measured value, the vertical dimension
from the wheel centre to the wheel cut-out,
must be input into the control unit using a
diagnostic tester in function 10 “Adaption”.
(Procedure, see Workshop Manual).
The codes serve to define the reference value
for normal level (allroad quattro 402 mm).
This means that design-specific values of the
level sensors are adjusted for this dimension.
Due to the tolerances of the components
involved, there is a certain deviation between
actual (measured) and reference (defined)
values.
By the inputting of the actual value, control
unit J197 recognises a potential difference to
the reference value. based on which the
design-specific values from the level sensors
are adapted.
Advantages of the measurement method:
•No influence of the correct basic setting
due to …
... different tread depths and tyre pres-
sures.
... minor unevenness of the road surface.
... different tyre sizes.
•Simple to perform.Codes for the allroad quattro
25500
Position Meaning
X00001 = Headlamp control not
installed
2 = Headlamp control installed
0X0005 = Reference height, front
axle 402 mm
00X005 = Reference height, rear axle
402 mm
000X00 = Vacant
0000X0 = Vacant
243_018
402 mm402 mm