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

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).

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

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

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

Service.For internal use only All rights reserved, including
the right to make technical
changes.
AUDI AG
Dept. I/VK-5
D-85045 Ingolstadt
Fax 0841/89-36367
940.2810.47.20
Technical status 11/00
Printed in Germany
Pneumatic suspension system
Par t 1
Selflevelling suspension
in the Audi A6Design and Function
Self-study programme 242
242
242