wheel 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

17
Air supply
The compressor
The construction and function of the
compressor corresponds largely to the unit
described in the self-levelling suspension of
the A6. The following is a description only of
the differences in the 4-level air suspension
system in the Audi allroad quattro
•The fitting location is outside the vehicle
and without noise insulation (in front of
spare wheel well).
•The operating pressure is increased to
16 bar owing to the pressure accumulator
system.
243_028
•Lower speed for reduced noise.
•Suction and discharge of the air is
performed from the spare wheel well via
an air filter/noise damper (passenger
compartment).
•An additional noise damper in the suction/
discharge line ensures minimal through-
flow noise, particularly during discharge.
•Temperature monitoring is performed via
a temperature sensor at the cylinder head
and a simulation formula in the control
unit (temperature model) (more
information, see Temperature sensor
G290).
CompressorValve unit with
pressure sensor G291
Pneumatic discharge valve
Discharge valve N11 Air dryerTemperature sensor G290Additional noise damperTo the air filter/noise damper
Electric motor
Pressure pipeSuction/discharge line Electrical connector
Compressor drive

18
System components
A special mounting consisting of spiral
springs and rubber damping elements
prevents the transfer of vibrations to the
bodywork.
You can find a description of the design and
function of the compressor as well as the
filling and discharging procedure in SSP 242.
243_008
In normal operation the compressor is
allowed to run only when the engine is
running.
Exceptions:
–Final control diagnosis
–Basic system setting
–In pre-run upon recognition of an
extremely low level
Mounting
243_009
Spiral springDamping element
Air filter/noise damper
Owing to the fitting location of the air filter/
noise damper in the spare wheel well, it
requires no maintenance.

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