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

21
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

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

27
Warning lamp K134...
... illuminates for one second when
terminal 15 is ON (self-test).
... is constantly illuminated in the
case of relevant system errors or
when the system is switched off.
... is constantly illuminated during
basic system setting and when
basic system setting has not been
performed successfully.
... flashes in the case of extremely
low or high levels.
... flashes during final control
diagnosis.
242_050 Warning lamp K134
As no magnetic materials are required,
temperature and age cause only minimal
variances in the measured values. Such
variances are caused by a reduction in the
strength of the magnetic field of permanent
magnets over time or due to temperature
changes. Level sensors, summary
The advantages of the angle sensor are the
proportional measurement process along
with their contact-free and therefore wear-
free operation.
The generation of ratios (proportional
measurement) means that the output signal
proportional to the angle is largely
independent of mechanical tolerances such
as distance changes, axle movement or
inclination errors. Magnetic interference is
also largely suppressed due to the generation
of ratios.

28
F
F
F
F
F
S
F
S
S F
3
1
7
52/25
2/50
2/49
2/05
2/04
2/01
2/02 9
10
4
8
System components
Control unit J197 transmits the information
concerning the vehicle level and the system
status back to the E281 via the K wire,
whereupon the electronic unit actuates the
relevant LEDs.
For self-diagnosis reasons, the “raise” button
is designed as a redundant additional
interface.
Operating unit for self-
levelling E281
The operation and displays of the operating
unit are described on page 7. In this section,
the function of the operating unit will be
described.
The interface to control unit J197 is
performed by means of a data
communication wire (K wire)
An electronic unit integrated into the
operating unit evaluates the signals from the
level button and transmits these as a
corresponding data protocol via the K wire
to control unit J197.
243_013
The K wire between E281 and J197
bears no relation to the self-diagnostic
K wire between J197 and the
diagnostic testers.
Electronic unit
Control unit J197 Terminal 30 Terminal 15
Raise button
K wire
Operating unit E281
Terminal 58s
Terminal
58d
to the ESP control unit
from the ESP control unit
HL2
HL1
NL
LL
man
High
Low
Lower button
ESP buttonF = LEDs for functional illumination
S = LEDs for switch illumination

29
CAN information exchange
In the case 4-level air suspension, the
information exchange between control unit
J197 for the self-levelling system and the
networked control units is performed via the
CAN drive with the exception of a few
interfaces.
Interfaces
The system overview shows the information
provided by the gearbox control unit via the
CAN bus which is received and used by the
networked control units.
Information sent by the J197
control unit.Information received and
evaluated by the J197 control
unit.
Engine control unit:
Engine speed
Self-levelling suspension control
unit J197
System status (OK or not OK)
Warning lamp (on/off)
Self-diagnosis
Fault memory entry
Type of vehicle (e.g. allroad
quattro):
Level status
Intermediate level
Parking level
Impending adjustment
Adjustment active
Raising level
Lowering level
Switching to FR
Switching to FL
Switching to RR
Switching to RL
ESP influence CAN drive high
CAN drive low
ESP control unit:
Driving speed
ESP status
For detailed information on the CAN
bus, please refer to SSPs 186 and 213.

30
The driving speed signal …
... is a square-wave signal produced by the
dash panel, the frequency of which is
changed in accordance with the vehicle
speed.
... is required in the evaluation of the driving
condition (stationary/driving mode) and
thereby for selection of the control criteria
(see “Control concept”).
The interface for the driving speed signal is
redundant, as the information regarding
speed is also transmitted by the CAN bus.
K wire
Communication for self-diagnosis between
control unit J197 and the diagnostic tester
takes place via the familiar K wire by means of
conventional data messages.
The self-diagnosis K wire must not be
confused with the K wire connecting
operating unit E281 to control unit J197.
Power supply to the headlamp range control
system
In the case of 4-level air suspension in the
allroad quattro, the headlamp range control
system voltage is supplied by the air
suspension control unit J197. Further
information can be found under Control unit
J197 on page 34.
Additional interfaces
The door contact signal …
... is an earth signal from the control unit for
central locking. It indicates that the door or
boot lid/tailgate is open.
... serves as a “wake-up pulse” for transfer
from sleep mode to run-on mode (see
“Control concepts”).
Terminal 50 signal...
... signals actuation of the starter and is used
to switch off the compressor during start-up.
If a low position is detected following a wake-
up pulse, the compressor is activated
immediately in order to allow the vehicle to
drive off as quickly as possible.
The compressor is switched off during start-
up in order to save battery power and ensure
starting power.
The vehicle locking signal …
... is used as information for parking level
control
... is an earth pulse coming from the control
unit for central locking J429
... is not detected by the self-diagnosis.
Parking level control is not performed if this
signal fails.
Interfaces
The vehicle locking signal is not
required for vehicles without parking
level control (see pages from 10
onwards and 34 onwards).