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

Service.For internal use only All rights reserved, including
the right to make technical
changes.
AUDI AG
Dept. I/VK-5
D-85045 Ingolstadt
Fax 0841/89-36367
040.2810.62.20
Technical status 11/00
Printed in Germany
Pneumatic suspension system Part 2
4-level air suspension
in the Audi allroad quattroDesign and function
Self-study programme 243
243
243

2

The 4-level air suspension system in the allroad quattro is a logical development of the self-
levelling system in the Audi A6.
The principles of the suspension/air suspension system and the description of those system
components which are identical in the 4-level air suspension system are described in SSP 242.
The contents of this self-study program are supplementary to the contents of SSP 242.
The 4-level air suspension system in the Audi allroad quattro

Introduction
Designing a vehicle this perfect for on and
off-road use sounds like squaring the circle.
Usually the strengths of an off-road vehicle
are decided weaknesses when it comes to
road use.
A high ground clearance, crucial for rough
terrain, gives the vehicle a correspondingly
high centre of gravity.
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243_002
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When it comes to fast cornering, however,
this is as disadvantageous as it is for driving
stability at higher speeds. In addition, the air
resistance is increased, which significantly
affects fuel consumption.
In contrast, the shorter spring travel and the
firmer running gear matching of an “on-road
running gear” offer inadequate driving
comfort off-road.
A variable ground clearance is the solution for
all road use and it’s called
4-level air suspension
.
The air suspension realised in the allroad
quattro is based on the familiar self-levelling
system of the Audi A6.

3
Contents
System description . . . . . . . . . . . . . . . . . . . . 4
The self-study programme is not intended as a workshop manual.
The self-study programme will provide you with information on
the design and functions of the different assemblies/systems.
New
NoteImportant:
Note
Page
For maintenance and repairs please refer to the current technical
literature.
Operation and display
Operation ................................................................................. 7
Display ..................................................................................... 8
Self-levelling suspension control unit J197 ....................... 34
Modes .................................................................................... 35
Control concepts
Service
Special tools .......................................................................... 38
Basic system settings .......................................................... 39
Self-diagnosis ....................................................................... 40
General overview .................................................................. 41
Control strategies
System components
Air springs .............................................................................. 14
Air suspension ...................................................................... 17
Diagram of pneumatic system ............................................. 20
Solenoid valves ...................................................................... 21
Temperature sensor G290..................................................... 22
Pressure sensor G291............................................................ 22
Level senders G76, G77, G78, G289 ..................................... 23
Warning lamp K134 ............................................................... 27
Operating unit E281 .............................................................. 28
CAN information exchange ................................................. 29
Additional interfaces ............................................................. 30
Function diagram ................................................................... 32
Interfaces
Control strategies, control unit 4Z7 907 553A ................... 10
Control strategies, control unit 4Z7 907 553B ................... 12
ESP safety switching ............................................................ 13
Order No.:

507.5320.01.00
This figure can be ordered as a size A0 poster through
Bertelsmann Distribution for a net price of DM
15.00 DM/7.50 EUR
.
Direct ordering through Bertelsmann only applies to Germany.
Dealers in export markets are requested to contact their importer.

4
Description of the system
The vehicle level is determined separately at
each axle side by means of 4 level sensors.
Each air suspension strut is allocated a so-
called air spring valve (transverse check valve)
so that each axle can be controlled
individually.
Front right air
suspension strutRear left suspension strut with load-
dependant damping.
Rear left vehicle
level sender
Control unit
Pressure accumulator
Operating unit
Rear left suspension strut
with load-dependant
damping.
Air supply unit with: Compressor
Discharge valve
Transverse check valves
Temperature sender
Pressure sender
Rear right vehicle
level sender
Electrical/pneumatic
lines
Front left air
suspension strut
Front left vehicle
level sender
Front right vehicle
level sender

The 4-level air suspension system is a fully-
supporting level control system with
conventional shock absorbers at the front
axle and load dependent shock absorbers
(PDC dampers) on the rear axle.
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5
The 4-level air suspension system is designed
as what is known as a pressure accumulator
system.
The pressure accumulator system increases
system availability, reduces noise
development and protects the power supply.One of the special features of the system is
the ability to alter the ground clearance by 66
mm in 4 stages. The 4 stages can be
controlled manually or automatically (see
page 7 onwards).
The levels are designated as follows:
Level 1 = low level (
LL)
Level 2 = normal level (
NL
)
Level 3 = high level 1 (
HL1)
Level 4 = high level 2 (
HL2)
Parking level
PL
= high level 1
High level 2 (HL2)
+41 mm from normal
level Ground clearance
208 mm
High level 1 (HL1)
+25 mm from normal
level
(=parking level)
Normal level (NL)
± 0 mm
Low level (TL)
-25 mm from normal
level Ground clearance
192 mm
Ground clearance
167 mm
Ground clearance
142 mm
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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.
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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
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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.

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
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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.

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O-ring
Locking cap

16
System components
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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.