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

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.

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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.

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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

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243_023
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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

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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

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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.

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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
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Cornering is detected by the J197 self-
levelling control unit by evaluation of
the signals from the four level sensors.
LL NL HL1HL2

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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.
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•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

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The 4 air spring valves N148, N149, N150,
N151 and accumulator valve N311 are
combined in one valve unit. They are
designed as 2/2 way valves and are closed
without current. The pressure on the air
spring side/accumulator side acts in the
closing direction.
The pressure lines are colour coded to
prevent confusion when connecting.
The colour allocation on the valve block is
echoed by corresponding coloured dots on
the connectors.
Solenoid valves
The 4-level air suspension has 6 electric
solenoid valves.
Discharge valve N111 forms a functional unit
together with the pneumatic discharge valve
and is integrated into the dryer housing (see
page 17).
Discharge valve N111 is a 3/2 way valve and is
closed without current.
The pneumatic discharge valve acts as a
pressure limiter and residual pressure
retaining device.
243_010Valve unit with
N148, N149, N150, N151
and N311
Compressor
pressure connectorFront leftPressure accumulator
Rear right
Rear left Front right

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System components
Function
The exciter coil is subjected to an alternating
current which produces an electromagnetic
alternating field, the induction of which is
penetrated by the rotor.
The current induced in the rotor produces a
second electromagnetic alternating field
around the conductor loop (rotor).
Both alternating fields, from the exciter coil
and from the rotor, act on the receiver coils
and induce corresponding alternating
currents in them.
While the induction of the rotor is
independent of its angle position, induction
of the receiver coils depends on their
distance from the rotor and thereby on its
angle position.
As the rotor, depending on its angle position,
overlaps differently with regard to each
receiver coil, their voltage amplitudes vary in
accordance with the angle position of the
rotor.
The evaluation electronics compensate the
alternating currents of the receiver coils,
amplify them and produce proportional
output voltages for the three receiver coils
(proportional measurement). After voltage
evaluation, the result is converted into output
signals for the level sensors and transmitted
to the control units for further processing.
0
0
0
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Exciter coil
Stator
Rotor
3 receiver coils
Conductor loop
(induced current)
U
1
U2
U3
Voltage amplitudes depending on the position of
the rotor with regard to the receiver coil
(example of a rotor position)
U1
U2
U3
Time
Time
Time
1st magnetic
field at the
exciter coil
2nd magnetic
field in the
conductor loop