AUDI A6 ALLROAD 1999 C5 / 2.G Pneumatic Suspension System
Page 21 of 44
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
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 4-level air suspension has 6 electric
Discharge valve N111 forms a functional unit
together with the pneumatic discharge valve
and is integrated into the dryer housing (see
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
243_010Valve unit with
N148, N149, N150, N151
pressure connectorFront leftPressure accumulator
Rear left Front right
Page 22 of 44
Temperature sensor G290
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
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_012 Temperature sensor G290
Pressure sensor G291Valve unit
Page 23 of 44
Vehicle level senders G76,
G77, G78, G289 (level
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
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.
Page 24 of 44
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
Level sensor on rear axle
Level sensor installation
Pin assignment for the level sensor
J431 Control unit for
J197 Self-levelling suspension control unit Pin
(left from J431, right from J197)
4 Analogue signal output,
(left only for HRC)
5 5 Volt power supply
(left from J431, right from J197)
6 Digital signal output,
(right and left for J197)
Page 25 of 44
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.
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.
Front of multilayer circuit board
with view of the receiver coils
Rear of multilayer circuit board
with view of the exciter coil
Page 26 of 44
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
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
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.
3 receiver coils
Voltage amplitudes depending on the position of
the rotor with regard to the receiver coil
(example of a rotor position)
ﬁeld at the
ﬁeld in the
Page 27 of 44
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
... ﬂashes in the case of extremely
low or high levels.
... ﬂashes during ﬁnal control
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-
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
Page 28 of 44
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
For self-diagnosis reasons, the “raise” button
is designed as a redundant additional
Operating unit for self-
The operation and displays of the operating
unit are described on page 7. In this section,
the function of the operating unit will be
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.
The K wire between E281 and J197
bears no relation to the self-diagnostic
K wire between J197 and the
Control unit J197 Terminal 30 Terminal 15
Operating unit E281
to the ESP control unit
from the ESP control unit
ESP buttonF = LEDs for functional illumination
S = LEDs for switch illumination
Page 29 of 44
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
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
Engine control unit:
Self-levelling suspension control
System status (OK or not OK)
Warning lamp (on/off)
Fault memory entry
Type of vehicle (e.g. allroad
Switching to FR
Switching to FL
Switching to RR
Switching to RL
ESP inﬂuence CAN drive high
CAN drive low
ESP control unit:
For detailed information on the CAN
bus, please refer to SSPs 186 and 213.
Page 30 of 44
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
... 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.
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
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.
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
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
The vehicle locking signal …
... is used as information for parking level
... 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
The vehicle locking signal is not
required for vehicles without parking
level control (see pages from 10
onwards and 34 onwards).