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

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.
243_021

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

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

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

22
p
Temperature sensor G290
(Overheat protection)
To enhance system availability, temperature
sensor G290 is attached to the cylinder head
of the compressor.
A temperature model is implemented in
control unit J197 which prevents overheating
of the compressor while simultaneously
utilising the maximum possible raising times.
For this purpose, the control unit calculates a
maximum permissible compressor
temperature based on the compressor
running time and the temperature signal, and
deactivates the compressor or prevents
activation when defined limit values are
exceeded.
System components
Pressure sensor G291
Pressure sensor G291 is integrated into the
valve unit and is used to monitor the pressure
in the pressure accumulator and the air
springs. The information regarding
accumulator pressure is required for checking
the plausibility of the raising functions (see
Pressure accumulator/control strategies,
Page 19) and for self-diagnosis. The individual
pressures of the air springs and pressure
accumulator can be determined by means of
appropriate control of the solenoid valves.
The measurement of individual pressures is
performed during discharging or filling of the
air springs/pressure accumulator. The
pressures determined in this manner are
stored and updated by the control unit.
The accumulator pressure is additionally
determined every 6 minutes (updated) while
the vehicle is in driving operation.
The G291 transmits a voltage signal
proportional to the pressure.
243_011
243_012 Temperature sensor G290
Pressure sensor G291Valve unit

23
Vehicle level senders G76,
G77, G78, G289 (level
sensors)
The level sensors are so-called angle sensors.
With the aid of the connecting link kinematics
unit, the height changes of the vehicle body
are converted into angle changes.
The angle sensor used in the Audi allroad
quattro is a contact-free sensor which
operates according to the induction principle.
A special feature of the level sensor used is
that it produces two different output signals
proportional to the angle. This allows it to be
used for both 4-level suspension and for
headlamp range control (see pin-assignment
table).
243_031
243_032
One signal output provides a voltage
proportional to the angle (for headlamp range
control) and a second signal output provides
and PWM signal proportional to the angle (for
4-level air suspension).
Level sensor on the front axle
Level sensor installation position
The 4 level sensors are identical in
design, only the brackets and
connecting link kinematics unit vary
according to the side and axle.
The sender arm deflection and thus the
output signal are opposite on the right
and left sides.
For instance, the output during
compression increases on one side and
decreases on the other.

24
System components
243_033
243_037
For technical reasons, the voltage for the left-
hand level sensors (front left G78 and rear left
G76) is supplied by the headlamp range
control unit J431. Power is supplied to the
right-hand level sensors (front right G289 and
rear right G77) by the 4-level air suspension
control unit J197.
This ensures that if control unit J197 fails, the
headlamp range control system can continue
to operate (see also Self-levelling control unit
page 34)
Level sensor on rear axle
Level sensor installation
position
Pin assignment for the level sensor
J431 Control unit for
HeadampRangeControl
J197 Self-levelling suspension control unit Pin
1 Earth
(left from J431, right from J197)
2 Vacant
3 Vacant
4 Analogue signal output,
Voltage signal
(left only for HRC)
5 5 Volt power supply
(left from J431, right from J197)
6 Digital signal output,
PWM signal
(right and left for J197)

25
The rotor consists of a closed conductor loop
connected to the sender arm (rotates with the
sender arm). The conductor loop has the
same geometric shape as the receiver coils.
Construction/design
The angle sensor consists essentially of the
stator and the rotor.
The stator consists of a multilayer circuit
board comprising the exciter coil, three
receiver coils and the control/evaluation
electronics. The three receiver coils have an
angular geometrical star shape and are
arranged out of phase. The exciter coil is
mounted on the back of the circuit board.
243_035
Operating lever
Conductor loop/rotor
Front of multilayer circuit board
with view of the receiver coils
Circuit board
connectors
Rear of multilayer circuit board
with view of the exciter coil
Control/evaluation
electronics

26
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
243_036
243_037
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