reset BMW 530I TOURING 1991 E34 Level Control System Manual

39
Level Control Systems
Workshop Hints
If a threshold level is exceeded on all 4 wheels when the vehicle is stationary, the control
unit assumes that the vehicle has been raised on a workshop platform.
There are three possible reset conditions for workshop platform recognition:
 The original level values are undershot at all four wheels,
 A selection is made by button,
 A speed of >40 km/h is recognized for 3 s.
Vehicle jack
If the lowering speed at a wheel is too low during the lowering operation, the system
assumes that the wheel is jacked up. However, the downward velocity must be less than
a certain preprogrammed speed threshold. If the system detects a jacked wheel, it stores
the height of this wheel.
Car jack recognition is reset when the stored ride height is again undershot. When a trav-
elling speed of 40 km/h is maintained for at least 3 s, another control attempt is performed.
The car jack recognition can also be reset by button selection.
Please note that the system also controls ride height in diagnostic mode. For this reason,
Belt Mode must be activated before carrying out work on the system or before setting the
vehicle ride height.
Belt Mode:
Heights are fixed and are not compensated. If Belt Mode is set, the function LED is off. The
text message "ride-height control system inactive" appears in the instrument cluster.
Transport Mode:
The Transport Mode setting is for transportation purposes. When the ignition is turned on,
the message "ride-height control system inactive" appears. Heights are increased or
decreased depending on ignition key status, e.g. ride height is reduced when the vehicle is
lashed to a ship or train and raised when the "Engine on" signal is generated and when the
vehicle is transported on a transporter truck.
The correct ride height is set to ± 5 mm via "Activate components." The left and right ride
levels are set separately at the rear axle. The ride levels are then set at the front axle. The
left and right air springs are adjusted jointly for this purpose.
Following this, the new ride height for the front and rear axles is stored via the "Offset func-
tion."
Before replacing components, the system must be depressurized! This is done in the diag-
nostics via "control unit functions," "Component activation," "Pressure-relieve front axle/rear
axle." Repeat the activation procedure 6 times.

52
Level Control Systems
Lift
The Lift mode is used to prevent control operations when a wheel is changed or during
work on the vehicle while it is on a lifting platform.
This mode is recognized when the permitted rebound travel at one or more wheels is
exceeded. For the E65/E66 the limit is > 55mm.
A “jack” situation is also recognized when the ride level is stored and the lowering speed
drops below the value of 2 mm/s for 3 seconds.
If the vehicle has been raised slightly and the permitted rebound travel has not yet been
achieved, the control operation attempts to readjust the ride height. If the vehicle is not low-
ered, a car jack situation is recognized after a specific period of time and this ride height is
stored.
A reset is performed if the vehicle is again 10 mm below this stored ride height.
Transport
The Transport mode is set and cleared by means of a diagnosis activation. It serves to
increase the ground clearance in order to ensure a safe transportation of vehicles on trans-
porter trucks. The nominal height of the vehicle is raised in this mode by 30 mm.
When the Transport mode is activated, the air suspension symbol is indicated in the vari-
able telltale in the instrument cluster and a text message is output in the Check Control
Display.
Control operations do not take place in this mode because the vehicle mass does not
change during transportation.
Belt
The Belt mode is set for mounting on the belt in order to avoid control operations.
When the Belt mode is activated, the air suspension symbol is indicated in the variable tell-
tale in the instrument cluster and a text message is output in the Check Control display.
The Belt mode is cleared by means of a diagnostic activation only. The Belt mode can no
longer be set.
New control units are supplied with the Belt mode set.
Control operations are not performed, the safety concept only operates with limited effect.
The Belt Mode is also known as “Band Mode” or “Assembly Line Mode”.

53
Level Control Systems
Operating Principle
Initialization/Reset Performance
When the control unit is powered up after a reset (such as an undervoltage < 4.5 V or by a
load cutoff), different tests and initializations are performed. This system is only enabled
after the tests have been successfully completed and starts to execute the control pro-
grams on a cyclical basis.
Occurring faults are stored and displayed.
Control Sequence
In an ongoing control operation, the high pass filter (fast filter) is always used to prevent the
controlled height from overshooting the nominal value. If a low pass filter (slow filter) were
used to calculate the ride height, brief changes of ride height would be consumed. The
low-pass filter is used while the vehicle is driven. This type of filtering filters out vibrations
which are excited by the road surface.
The high pass filter is used to respond quickly to ride level deviations from setpoint. These
take place while the vehicle is stationary in the event of large load changes.
Both sides of the vehicle are controlled individually, i.e. even the setpoint/actual value com-
parison for both sides is carried out individually. Exception: check for undershooting of the
minimum height in Pre-mode and Kerf mode: consideration of the left and right mean val-
ues in each case.
The following stipulations are applicable here:
 Raising before lowering
 Activation of all valves with control in the same direction
 Individual wheel deactivation
To ensure safe closing of the non-return valve in the air drier, the drain valve is actuated
briefly for 200ms after the control operation has ended.
The permissible ON period of the components is monitored while control up operation are
executed.

54
Level Control Systems
Safety Concept
The safety concept is intended to inhibit any system malfunction, particularly unintentional
control operations, through monitoring of signals and function relevant parameters. If faults
are detected, the system is switched over or shut down depending on the affected com-
ponent. The driver is informed of existing faults via the display. Detected faults are stored
for diagnostic purposes.
In order to ensure high system availability, existing faults, as far as possible, are cleared with
terminal 15 ON. This is done by resetting the fault counter to zero. However, the fault
memory content in the EEPROM is retained and can be read out for diagnostic purposes.
The system is then operational again. The fast troubleshooting helps to detect existing
faults before control operation can take place.
Only lowering is permitted if:
 The permissible supply voltage of 9 volts is undershot
 The permissible compressor running time of 480 seconds is exceeded.
A reset takes place if the voltage is in the OK range of 9 to 16 volts or after the compres-
sor pause time of 100 seconds has elapsed.
Only raising is permitted if:
 The permissible control down period of 40 seconds is exceeded
 The reset takes place the next time the vehicle is driven or after the next control up
operation.
No control operation takes place if:
 The permissible supply voltage of 16 volts is exceeded
The reset takes place as soon as the voltage is in the OK range.