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
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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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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.

8
Operation and display
If the actual level deviates greatly from the
reference level, this is indicated to the driver
with flashing LEDs (according to a level
change).
Significant deviations are:
– at least one axle level is below the next
level down.
– both axle levels are above the next level up.
Display
The four LEDs which are arranged one on top
of the other in the display zone illuminate
continuously to indicate the current level
status.
Only the control procedure which has been
triggered by a level change (whether
automatically or manually) is indicated by one
or several flashing LEDs. Once the target level
has been reached, the flashing changes to
continuous illumination.
The LEDs in the “raise” and “lower” buttons
indicate actuation and the control direction. If
the LED flashes, a level request has been
denied (e.g. if the driving speed is too high)
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Lower button Raise button ESP button
Manual mode display
Display zone with 4 level-indicating LEDs Actuation/control direction display Actuation/control direction display

9
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Other button functions
Automatic switching
The so-called “manual mode” can be
switched on or off by pressing the “raise” or
“lower” button for at least 3 sec. The yellow
LED marked “man” indicates to the driver that
the vehicle is in manual mode.
The automatic “parking level control” and
“motorway mode” functions are deactivated
in manual mode.
Switching off control system
The control system is switched on or off by
pressing both level buttons for longer than
5 seconds.
When the control system is switched off, the
LEDs in the operating unit for manual mode,
both level buttons and the warning lamp K134
are illuminated.
The level-indicating LEDs show the level set.
The corresponding LED is continuously
illuminated.
A control system that has been switched off
will be automatically switched back on again
when the driving speed exceeds approx.
10 km/h (unless the lifting platform mode is
recognised).
The control system can also be switched off
using the diagnostic testers (see Workshop
Manual).
It is often advisable to switch off the
system during repair work (e.g. during
axle measurement or if the pressure
lines have been detached) in order to
prevent the compressor from running
unnecessarily.
Display example: Manual mode and NL
Display example: Raising from LL to HL1
Display example: Raising from HL1 to HL2
Display example: Lowering from NL to LL

10
If the vehicle is at high level 2, it will lower
automatically to high level 1 at a speed of
> 35 km/h. The system will respond to a
request to shift to high level 2 only up to a
speed of < 30 km/h.
At a speed of > 80 km/h in high level 1, the
system will automatically lower the vehicle to
normal level.. The system will respond to a
(manual) request to shift to high level 1 only
up to a speed of < 75 km/h.
During driving operation, no automatic
raising to high level 1 or 2 is performed. It
must be selected manually by the driver.
The parking level is an exception. In this
mode the vehicle automatically rises to high
level 1 once it has been parked and locked
(see parking level control). There are two control units currently in use,
depending on the country.
The control strategies described below relate
to the control unit 4Z7 907
553A.
The differences in control units with part
numbers 4Z7 907
553B
are described
subsequently.
See also page 34, “Self-levelling control unit
J197”.
Control strategies
4Z7 907 553A
Automatic lowering
As mentioned previously, the driver can select
the appropriate level by actuating the “raise”
or “lower” buttons.
The following preconditions relating to
driving speed apply for high level 1 and high
level 2.
Control strategies
0 35 80 120
0
5 35 70 120

Automatic lowering
Lowering processes
after 30 seconds
after 30 seconds
Raising processes
after 120 seconds
Raising to parking level
Immediate raising Speed km/h
Speed km/h
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LL NL HL1HL2
LL NL HL1HL2