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

7
Operation and display
Operation
The self-levelling control unit E281 is used to
control the 4-level air suspension and the
display/monitor the system status.
Certain level changes occur automatically
during normal driving (see Control strategy).
Within defined conditions (see Control
strategy) the driver can use the “raise” or
“lower” buttons to select an appropriate level
at any time. Pressing the “raise” button once selects the
next highest level. By pressing the button
repeatedly, it is possible to change, e.g.
directly from low level to high level 1. High
level 2 cannot be selected until high level 1
has already been set.
Changing to a lower level is performed in the
same manner as described above using the
“lower” button. By pressing several times (x3)
it is possible to shift directly from high level 2
to the low level.
Operating unit for self-levelling E281
241_062
It is possible to switch to a higher level
only when the engine is running or
when sufficient pressure is present in
the pressure accumulator.
It is possible to change to a lower level even
when the engine is switched off.

18
System components
A special mounting consisting of spiral
springs and rubber damping elements
prevents the transfer of vibrations to the
bodywork.
You can find a description of the design and
function of the compressor as well as the
filling and discharging procedure in SSP 242.
243_008
In normal operation the compressor is
allowed to run only when the engine is
running.
Exceptions:
–Final control diagnosis
–Basic system setting
–In pre-run upon recognition of an
extremely low level
Mounting
243_009
Spiral springDamping element
Air filter/noise damper
Owing to the fitting location of the air filter/
noise damper in the spare wheel well, it
requires no maintenance.

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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.

35
Level change process:
Raising - rear axle first, then front axle
Lowering - front axle first, then rear axle
Modes
Height mode/driving mode
Reaction times upon level deviation
Control characteristics during level change
Level change is basically performed axle by
axle, whereby level differences between the
left and right sides are compensated (e.g. if
loaded on one side).Driving speed Reaction time
<5 km/h
Height modeapprox. 5 seconds
approx. 1 second at
extremely low level
>10 km/h
Driving modeapprox. 50 seconds or
15 minutes
depending on the level
deviation
Run-on mode/run-up mode
The run-on mode enables the compensation
of level deviations after the vehicle has been
parked (e.g. caused by passengers leaving the
vehicle or unloading the vehicle) and before
driving off (e.g. caused by intense cooling,
leakage or loading).
In this mode, delay times before commencing
a journey are kept to a minimum.After “Ignition OFF”, the control unit is in the
so-called run-on mode. The control unit
remains active for a maximum of 15 minutes
(via terminal 30) until it goes into sleep mode.
Due to the limited energy available when the
engine is switched off, control limits are
extended and controls are limited in both
number and duration.

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Allroad quattro control strategies
4-level air suspension + additional shift stage
0203580 60
5100 120 130 200
30
General overview
Control unit 4Z7 907 553A/B
ESP safety-switching
Automatic lowering
Parking level
control
v >70 km/h: Engine intervention
v >50 km/h: Acoustic and visual warning in low range
Air supply: control primarily via
pressure accumulator <36 km/hVehicle speed v
in km/h
v <30 km/h: shift to low range possible
Additional shift stage
Air supply: control primarily via compressor >36 km/h
Pressure accumulator filled >36 km/h
Motorway mode:Lowering: >120 km/h >30 seconds
Raising: <70 km/h >120 seconds
<35 km/h >30 seconds
<5 km/h immediately
Manual mode:- no parking level control
- no motorway mode
- automatic lowering from HL2
and HL1; ESP safety-
switching remains active
Automatic mode:- parking level control (HL1)
- motorway mode:
- automatic lowering from HL2 and HL1.
- ESP safety-switching
LL NL HL1 HL2243_040
Control unit 4Z7 907 553B: Automatic mode:- no parking level control
- automatic raising to HL1
<60 km/h >30 seconds
<30 km/h immediately