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

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)

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).

31
123
1 237 8496513
BL NSL 31 58l RF BR 30 34 58r 3110 11 12
The trailer operation signal …
..... comes from the F216 contact switch in the
trailer socket.
When the plug is connected, contact switch
F216 connects control unit J197 to earth.
See also “Trailer operation”.
Headlamp range control signal
As changing vehicle levels is axle-based (i.e.
for both sides of an axle at once), this would
produce a short-term visibility range
reduction when driving at night.
For this reason, the allroad quattro is fitted
with an automatic dynamic headlamp control
system (also without gas-discharge
headlamps). The automatic dynamic
headlamp range control system maintains the
light beam at a constant angle while the
vehicle level changes.
In order to prevent irregularities in the road
surface, such as bumps or potholes, from
causing the headlamp range to alter
unnecessarily, long reaction times are set
when the vehicle is travelling at relatively
constant speeds (little or no acceleration). If level change takes place (e.g. motorway
mode), the 4-level air suspension control unit
J197 transmits a voltage signal to the
headlamp range control unit J431.
This activates the HRC immediately and
controls the bodywork movements.
Level change process:
Raising - rear axle first, then front axle
Lowering - front axle first, then rear axle
243_014
Trailer socket to the self-levelling suspension
control unit J197 (pin 2/10)
from the rear fog light
switch
F216

33
Key to function diagram
E281 Self-levelling suspension operating
unit
F216 Contact switch for switchable rear fog
light
G76 Self levelling suspension sender, RL
G77 Self levelling suspension sender, RR
G78 Self levelling sender, FL
G289 Self levelling suspension sender, FR
G290 Compressor temperature, self-
levelling suspension sender
G291 Self-levelling suspension pressure
sender
J197 Self-levelling suspension control unit
J403 Relay for self-levelling suspension
compressor
J429 Control unit for central locking
J431 Control unit for headlamp range
control
N111 Discharge valve for self-levelling
suspension
N148 Valve for FL suspension strut
N149 Valve for FR suspension strut
N150 Valve for RL suspension strut
N151 Valve for RR suspension strut
N311 Valve for self-levelling suspension
pressure accumulator
K134 Self-levelling suspension warning
lamp
V48 Left headlamp range control motor
V49 Right headlamp range control motor
V66 Self-levelling suspension compressor
motor= Input signal
= Output signal
= Positive
= Earth
= Bi-directional
= CAN bus/signal wire
Auxiliary signals:
CAN low
CAN high
Door contact signal
Diagnostic connector for K wire
Vehicle locked signal
Trailer operation signal (F126)
Terminal 50 signal
Driving speed signal
Terminal 56
Diagnostic connector for K wire
to the instrument cluster
Driving speed signal from ABS control unit,
speed sensor output, rear left
1
2
3
4
5
6
7
8
I
II
III
IV
Terminal 58s
Terminal 58d
ESP button
ESP button
A
B
C
DHeadlamp range control signal
9
Power supply J431
10

34
However, all level sensors (left and right) are
required in the air suspension system run-up
and run-on mode (ignition OFF).
To allow the left-hand level sensors to deliver
measured values in the case of the 4-level air
suspension in the allroad quattro, power is
supplied to control unit J431 (HRC) from
control unit J197).
This ensures that voltage is supplied to all
level sensors when control unit J197 is active.
Self-levelling suspension
control unit J197
The central element of the system is the
control unit which, in addition to its control
functions, enables the monitoring and
diagnosis of the entire system.
The control unit detects the signal from the
level sensors and uses it to determine the
current vehicle level. This is compared with
the reference level and corrected if necessary,
depending upon further input variables
(interfaces) and its internal control
parameters (reaction times and level
deviations).
It differentiates between various control
situations and controls them via the relevant
control concepts (see Control concept).
Comprehensive self-diagnosis facilitates
inspection and service of the system (see
Workshop Manual).
There are two control units currently in use,
depending on the country.
Control units with the part numbers
4Z7 907 553A and 4Z7 907 553B have different
control strategies (see page 10 onwards).
A common control strategy for all countries
(as for Index “B”) is planned for the future.
Control concepts
243_039
The system can be tested via the self-
diagnosis or test adapter 1598/35.
For further information, see “Service”
chapter.
Address word 34
Power supply to the headlamp range control
system
As previously described in the “Level sensors”
section, voltage is supplied to the left-hand
level sensors by the headlamp range control
unit J431)
Headlamp range control requires neither run-
up nor run-on times, so the voltage is
normally supplied to control unit J431 via
terminal 15 (ignition ON) (see function
diagram, page 32).

39
Basic system setting
The basic system setting of the reference
level in the 4-level air suspension system is
performed by inputting body-level measured
values at normal level.
The measured value, the vertical dimension
from the wheel centre to the wheel cut-out,
must be input into the control unit using a
diagnostic tester in function 10 “Adaption”.
(Procedure, see Workshop Manual).
The codes serve to define the reference value
for normal level (allroad quattro 402 mm).
This means that design-specific values of the
level sensors are adjusted for this dimension.
Due to the tolerances of the components
involved, there is a certain deviation between
actual (measured) and reference (defined)
values.
By the inputting of the actual value, control
unit J197 recognises a potential difference to
the reference value. based on which the
design-specific values from the level sensors
are adapted.
Advantages of the measurement method:
•No influence of the correct basic setting
due to …
... different tread depths and tyre pres-
sures.
... minor unevenness of the road surface.
... different tyre sizes.
•Simple to perform.Codes for the allroad quattro
25500
Position Meaning
X00001 = Headlamp control not
installed
2 = Headlamp control installed
0X0005 = Reference height, front
axle 402 mm
00X005 = Reference height, rear axle
402 mm
000X00 = Vacant
0000X0 = Vacant
243_018
402 mm402 mm