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

11
Motorway mode
If the vehicle travels for longer than
30 seconds at over 120 km/h (vehicle is
already at normal level), it will automatically
be lowered to low level.
This reduces air resistance (saves fuel) and
lowers the vehicle’s centre of gravity
(improved driving dynamics).
PL (=HL1) is only cancelled when a
driving speed of 80 km/h is exceeded
(see automatic lowering) or when
switching to a lower level manually.
If the vehicle is already in HL2 it is not
lowered to parking level.
Manual mode
The motorway mode and parking level
control functions are deactivated in
manual mode (see Automatic
switching page 9).
The vehicle rises automatically to normal level
at the following speeds and time thresholds:
Vehicle speed Time
<70 km/h >120 seconds
<35 km/h >30 seconds
<5 km/h immediately

Parking level control
The parking level ensures that the vehicle is
maintained at a suitable level after parking for
a long period of time (normal volumetric
reduction due to cooling or diffusion).
It also facilitates entering and loading the
vehicle and optimises the appearance of the
stationary vehicle.
The parking level corresponds to high level 1
(HL1).
The vehicle is set to parking level
–when the system is in run-on mode and the
vehicle is locked from the outside.
–when sufficient pressure is present in pres-
sure accumulator.
–when the system is not switched to manual
mode.

12
Control strategies
The vehicle rises automatically to high level 1
at the following speeds and time thresholds:
If the system has lowered the vehicle to low
level (motorway mode), it will automatically
raise it to high level 1 when its speed drops
below 60 km/h for longer than 30 seconds.Vehicle speed Time
<60 km/h >30 seconds
<30 km/h immediately
Control unit strategies
4Z7 907 553B
Variations to the description of control unit
4Z7 907 553A are outlined below:
•No parking level control
•Automatic raising to high level 1
Preconditions for automatic raising to high
level 1:
•The system must not be switched to
manual mode.
•Between ignition ON and OFF, the driver
must select high level 1 or high level 2
once.
243_019
Automatic lowering
Lowering processes
after 30 seconds
Automatic raising to HL1 after
30 seconds
Raising processes
Immediate raising Speed km/h
Speed km/h LL NL HL1HL2
LL NL HL1HL2

13
If, for example, the vehicle is at high level 2
with active ESP influences and the driver
accelerates sharply on a very winding route,
speeds of > 35 km can be achieved in high
level 2. In order to guarantee maximum safety
in such driving conditions, ESP influences are
automatically deactivated at a speed of
> 70 km/h, despite the high centre of gravity
of the vehicle (ESP-safety switching).
Normal ESP functions are available again and
the ESP warning lamp extinguishes.
This ESP safety switching takes place as of
70 km/h at high level 2 and as of 120 km/h at
high level 1.
There is no ESP safety switching at normal
level or low level.
ESP safety switching
For technical reasons it is not possible to
change levels/self-level during cornering. If
cornering is recognised, no control functions
are performed and control functions already
running are interrupted. The target level
remains stored and is reset when straight-
ahead driving is recognised.
In the Audi allroad quattro it is possible to
influence certain ESP functions using the ESP
button.
You can find further information about this in
SSP 241, from page 67 onwards.
If ESP influences have been activated (via ESP
button, ESP warning lamp illuminated), the
transverse dynamics control (anti skid
function) is passive (not during braking).
0 35 80 12070

ESP switching at high level 2
No self-levelling while
corneringESP switching at high level 1
Speed km/h No self-levelling while
cornering
243_027
Cornering is detected by the J197 self-
levelling control unit by evaluation of
the signals from the four level sensors.
LL NL HL1HL2

14
The air springs
The front air spring is a new design.
As on the rear axle, the air springs are combined
coaxially with the dampers as a suspension strut.
The rear air springs are identical in design and
function to those of the Audi A6 with self-levelling.
Design
While in the case of the rear suspension strut, the
connection/seal from the air spring (piston) to the
damper is made via a double-seal bayonet
connection, on the front suspension strut it takes the
form of a single-seal N17 connector.
The differences in design require a different
assembly.
Front suspension strut
The assembly of the front air spring with the damper
is carried out without lubrication. The N17 connector
and the O ring must be absolutely dry and free from
grease.
Before assembly of the air spring, the O-ring
is placed onto the second shoulder of the damper,
ensuring an even perimeter. The air spring (piston) is
positioned onto the damper and pushed together
with adequate force. The O-ring is forced onto
shoulder 3 by the movement of the piston, where it
supports and seals the air spring.
System components
243_004
Installation
O-ring
O-ring
Air connection

15
Rear suspension strut
The bayonet connection must be absolutely
clean and is greased with a special lubricant
before installation (see Workshop Manual).
For installation, the air spring is pushed on
and then turned.
Operating pressure of the air springs
front rear
Minimum
operating
pressure6.0 bar 6.1 bar
Nominal
operating
pressure6.4 bar 8.5 bar
Maximum
operating
pressure9.0 bar 10.9 bar
Always check for leaks on the O-ring
seals at the raised areas. The sealing
surfaces must be clean, free from
corrosion and pitting (aluminium parts)
and greased as required (see Workshop
Manual).
Design and function of the rear air
springs, see SSP 242, from page 40
onwards.
Full description of the PDC damper, see
SSP 242, from page 33 onwards.

243_005
O-ring
Locking cap

16
System components
243_006
243_007
WrongCorrect
Air springs must not be moved when
pressureless because the air bellows
cannot unroll on the piston and would
be damaged.
In a vehicle with depressurised air
springs, the relevant air springs must
be filled with the aid of the diagnostic
tester (see Workshop Manual) before
raising or lowering the vehicle (e.g. on a
vehicle lifting platform or vehicle jack).
Warning:
The piston must not be touched during
installation or transport of the
complete suspension strut assembly as
the piston can be easily pushed back
when unpressurised.
If the sealing ring is pushed out of
position (by the air spring pressure) the
air spring will not be sealed correctly.

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.

19
Pressure accumulator
The pressure accumulator allows the vehicle
level to be raised more rapidly with minimal
noise as the pressure accumulator is only
filled while the vehicle is in driving operation
and the compressor noise is less noticeable
(see air supply strategy).
Provided that there is sufficient pressure in
the pressure accumulator, vehicle level
raising can be performed without the
compressor.
Sufficient pressure means that before the
vehicle is raised there must be a pressure
difference of at least 3 bar between the
pressure accumulator and the air springs.
The pressure accumulator is made of
aluminium and has a storage volume of
approx. 6.5 l. The maximum operating
pressure is approx. 16 bar.
243_029
Air supply strategy
At driving speeds of < 36 km/h air supply is
effected primarily by the pressure
accumulator (provided sufficient pressure is
available).
The pressure accumulator is only filled when
driving at speeds of 36 km/h and above.
At a driving speed of > 36 km/h the air supply
is primarily from the compressor.
This supply strategy ensures virtually
noiseless system operation and reduces the
current consumption.
Pressure accumulatorPressure connector

20
System components
p
Pneumatic diagram
1 Additional noise damper
2 Non-return valve 1
3 Air dryer
4 Non-return valve 3
5 Non-return valve 2
6 Discharge throttle
7 Pneumatic discharge valve
8 Compressor V66
9 Electric discharge valve N111
10 Pressure sensor G291
243_030
1234
6
5
79
10
1112131415
16
17181920
11 Valve for pressure accumulator N311
12 Valve for FL suspension strut N148
13 Valve for FR suspension strut N149
14 Valve for RL suspension strut N150
15 Valve for RR suspension strut N151
16 Pressure accumulator
17 Front left air spring
18 Front right air spring
19 Rear left air spring
20 Rear right air spring
from the compressor
relay from control unit
to the
control unit from the
control unit
8