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

51
Valve for suspension strut
rear left N150 and rear
right N151
Valves N150 and N151 are described as
transverse check valves and are combined in
one housing.
Both transverse check valves are so-called
2/2 way valves (2 connections and 2 switching
positions). The transverse check valves are
used to Þll and discharge the air springs. The
valves are closed without current and prevent
an undesirable pressure equalisation
between the left and right-hand air springs.
This prevents the air spring pressure of the
outer wheel (higher air spring pressure)
escaping to the inside wheel (lower air spring
pressure) when cornering. This would result
in a momentary tilt of the vehicle.
The transverse check valves are always
controlled in unison during raising and
lowering as adjustment can only be
performed for the whole axle (see level
sensor).
Following a control process while the vehicle
is in driving operation (v >10km/h) the
transverse check valves are opened three
times for approx. 3 seconds at intervals of
approx. 12 seconds in order to equalise the
pressure between the left and right-hand air
springs.
If, for example, a control process takes place
while cornering, this will cause the rear axle
to tilt. The tilt is compensated by the opening
of the transverse check valves, as described
above (not in the case of a one-sided load).
242_036
The self-levelling system in the Audi A6
is not able to compensate for one-sided
loads (level difference between left and
right). To prevent differing pressures in
the air springs the transverse check
valves are opened as described after a
control process.
242_012by control unit J197N150
N151

52
Self-levelling suspension, A6
Self-levelling
suspension sender G84
The vehicle level is detected by the self-
levelling system G84 sender (level
sensor).
A contact-free angle sensor is used to
determine the spring compression
between the rear axle and the bodywork
with the aid of the connecting link
kinematics unit.
The connection of the connecting link
kinematics unit (see Þgures 242_044 and
242_045) is designed to largely
compensate for one-sided compression.
This connection allows self-levelling to
operate using only one level sensor.
The self-levelling system in the Audi A6
is not able to compensate for different
levels on the left and right-hand sides
(e.g. due to one-sided loads).
Pin assignment for level sensor G84
J197 Self-levelling suspension
control unit Pin
1 Earth (from J197)
2 Vacant
3 Vacant
4 Analogue signal output,
voltage signal
5 5 Volt voltage signal
(from J197)
6 Vacant
242_044 Self-levelling suspension sender G84
Connecting link
Axle cross member
Connection to the torsion beam axle assembly in the front
wheel drive version
Bracket (attached to chassis)
Connecting link Self-levelling suspension sender G84
Bracket
Anti-roll bar
Connection for quattro drive with double-wishbone axle
242_045
Sub-frame
The angle sensor operates according to the
Hall principle. Evaluation electronics
integrated into the sensor convert the signal
of the Hall IC into a voltage signal
proportional to the angle (see diagram).

53
0,5 2,5 4,5
0°
70°
0
Function
A ring magnet is connected to the axle of the
sensor crank (rotor).
A hall IC is positioned eccentrically between a
two-piece iron core (stator). It forms a single
unit together with the evaluation electronics.
Depending on the position of the ring
magnet, the magnetic Þeld which penetrates
the Hall IC changes.
The resulting Hall signal is converted by the
evaluation electronics into a voltage signal
proportional to the angle. The control unit
J197 uses this analogue voltage signal to
determine the current vehicle level.
242_062242_061
242_060
Deßection 35¡ right No deßection
Deßection 35¡ left
Rotor
(ring magnet)
Stator
(divided iron core)
N
SN
S
N
S
Angle VoltsHall IC
Average setting
approximate reference level position
242_063
The angle sensor described here is
also used for the automatic
headlight range control system.
A total of 3 sensors are Þtted into
vehicles with automatic headlight
range control.

54
Self-levelling suspension, A6
Self-diagnosis system G84
If the G84 fails, no self-levelling is possible.
The system initiates the appropriate
emergency operation mode.
The G84 is adjusted by adapting the reference
level with the aid of the diagnostic tester and
spacer gauges T40002 (see Workshop
Manual).
242_055
T40002
198_039
Self-levelling control unit
J197
The central element of the system is the
control unit which, along with its control
functions, enables the monitoring and
diagnosis of the entire system.
The control unit detects the signal from the
level sensor and uses it to determine the
current vehicle level. This is compared with
the reference level and corrected if necessary
depending on further input variables
(interfaces) and its internal control
parameters (Þlter times and level tolerances).
It differentiates between various control
situations and controls them via the relevant
control concepts (see Control concept).
Comprehensive self-diagnosis facilitates
inspection and servicing of the system (see
Workshop Manual).
Address word 34
242_004
VAS 5051

55
Self-levelling suspension
warning lamp K134
The warning lamp É
... is constantly illuminated in the case of
corresponding system errors or when the
system is switched off.
... ...ßashes in the case of extremely low or
high levels. <Ð55 mm/>+30 mm.
... ... ßashes during Þnal control diagnosis.
... ßashes when the control system is
switched off (only possible with diagnostic
tester).
After switching off the ignition, K134
illuminates for a function check and
extinguishes after the control system has
performed internal control unit test sequence
(unless an error is present).
Warning lamp K134
242_050
The vehicle should not be driven as
long as the warning lamp is ßashing, as
low vehicle parts may be damaged due
to inadequate ground clearance.
If the warning lamp remains on
continuously to indicate a system error,
the system is switched off.
The driver is requested to contact the
nearest Audi service centre.

56
Self-levelling suspension, A6
M
+ -+ -+ -
31
1234
Functional diagram
C11 Condenser
G84 Self-levelling suspension sender
J197 Self-levelling suspension control unit
J403 Relay for self-levelling suspension
compressor
K134 Self-levelling suspension warning
lamp
N11 Discharge valve
N150 Rear left strut valve
N151 Rear right strut valve
S Fuse
V66 Compressor motor
T. 30T. 15T. 30
242_001 S SJ403
V66
N111 N150 N151 K134
J197
G84
= Input signal
= Output signal
= Positive
= Earth
= bi-directional
1 Diagnostic interface
2 Driving speed signal
3 Door contact signal
4 Terminal 50 signal
C11

57
The interfaces
The driving speed signal
(a square wave signal processed by the dash
panel insert, the frequency of which changes
analogously to the speed)
is required in the evaluation of the driving
condition (stationary/driving mode) and
thereby for the selection of the control
criteria (see ÒControl conceptÓ). 1 wheel revolution
Signal T.15 ...
... is used for the evaluation of the system
status, run-on, stationary, driving and sleep
modes.
Signal T. 50 ...
... signals the control of the starter and is
used to switch off the compressor during the
starting process.
If a low position is detected after a wake-up
pulse, the compressor is actuated
immediately in order to allow the vehicle to
drive off as quickly as possible.
The compressor is switched off during the
starting process to protect the battery and
ensure starting performance. The door switch signal...
... is an earth signal from the control unit for
central locking. It signals that the door or
boot lid/tailgate is open.
... serves as the Òwake-up pulseÓ for the
transition from sleep mode to run-on mode
(see ÒControl conceptÓ).
Driving speed signal (4 pulses)
Signal from speedometer sender (reed contact)
We speak of run-on mode even if the
system is currently in Òrun-upÓ mode
(after a wake-up pulse before
commencing driving).
198_069

58
Self-levelling suspension, A6
The control concept
Stationary mode
The stationary mode is recognised at a speed
of <5 km/h.
In stationary mode, vehicle level deviations
due to e.g. passengers entering or leaving the
vehicle, or due to loading or unloading the
luggage compartment, are readjusted within
a short response time, in order to restore the
reference level as far as possible even before
the journey has begun.
The response time is 1 or 5 seconds,
depending on the level deviation. If the
deviation is great (extremely low position) the
response time is 1 second, at lesser level
deviations (normal deviation) it is 5 seconds. Driving mode
The driving mode is recognised at a speed of
>10 km/h.
In driving mode, level changes in the air
springs caused by fuel consumption or
temperature-related volumetric changes
(changing ambient temperatures) are
adjusted.
So that acceleration or braking does not
affect the control system, long response
times are set in the driving mode.
The response times are between 50 seconds
and 15 minutes depending on the control
thresholds.
Driving mode
Stationary mode
Run-on mode/run-up modeSleep mode
Control process

59
Sleep mode
To minimise electricity consumption the
control system switches to Òsystem idleÓ
(sleep mode) after 15 minutes.
There is no level adjustment in sleep mode.
ÒWake-upÓ is primarily triggered by the door
switch signal.
If the door switch signal fails, the system is
activated when the ignition is switched ÒONÓ
or by the driving speed signal.
The system can switch between sleep mode
and run-up mode, triggered by the door
switch signal, a maximum of 5 times. After
this, the system can only be activated via
terminal 15 and/or the driving speed signal. Run-on mode/run-up mode
After ÒIgnition OFFÓ, the control system is in
the so-called run-on/run-up mode. The
control unit remains active for a maximum of
15 minutes (via terminal 30) until it goes into
sleep mode.
The run-on/run-up mode is used to adjust
level deviations after parking the vehicle or
prior to starting on a journey.
The limit value in the rebound direction is
increased by 25 mm in the run-on/run-up
mode so that when the driver and/or the
passenger re-enters the vehicle, it does not
sink lower than the reference level or in order
to minimise any necessary vehicle raising
period.
The same response times apply as those
indicated for the stationary mode.

60
Self-levelling suspension, A6
Other features of the
control concept
Lifting platform mode
System behaviour:
If the vehicle is raised on a lifting platform the
system will react in the same manner as for a
level increase, by discharging the air spring
pressure.
The vehicle body would normally lower at this
point. Lowering ceases once the reference
level is reached.
As, however, the reference level is not
reached when a vehicle is raised on a lifting
platform, the air spring pressure would
continue to discharge down to the residual
supporting pressure. To prevent this
happening, the control system incorporates a
lifting platform mode.
This evaluates the level signal during the
discharge process and recognises a lifting
platform (no lowering, despite discharge),
whereby the system switches to lifting
platform mode.
When it recognises a lifting platform,
discharge stops and lowering ceases.
The system exits lifting platform mode by
means of the evaluation of further input
signals.It is normal for the rear axle to sink
after placing the vehicle onto the lifting
platform as a certain amount of time
will elapse before the system switches
to lifting platform mode and will
therefore release some pressure.
242_001