ignition BMW 525I TOURING 1995 E39 Level Control System Manual

38
Level Control Systems
All control operations in advance / overrun mode are executed as long as pressure is avail-
able in the accumulator. When the accumulator is empty and the engine is turned off, con-
trol operations are directly driven by the compressor. User-activated changes of ride level
and filling of the accumulator are not possible.
Terminal 15
As soon as the ignition is turned on (terminal 15), the user is allowed to lower the ride level
as required.
However, it is still not possible to raise the ride level or fill the accumulator.
Ride level is compensated outside a narrow tolerance range of 10 mm upwards and 10 mm
downwards.
Engine "on"
Ride level compensation, raising and lowering the vehicle's ride height as well as filling the
accumulator are permitted when the engine is running. The compressor also starts up dur-
ing every control operation.
Ride level is still compensated outside the narrow tolerance range of ±10 mm.
As long as the vehicle is stationary, high speed filtered ride level signals are used to detect
a change of load. This allows the system to react immediately to changes in ride level.
As soon as the vehicle is travelling, it changes over to low speed filtered ride-level signals.
The system no longer reacts to bump movements caused by road surface unevenness. A
mean value is formed over a prolonged period of time, i.e. payload is only altered by the
progressive emptying of the fuel tank.
The high speed filter is not used until the vehicle is stationary again and a lid is opened. If
no lid is opened, the vehicle logically cannot be loaded or unloaded.
SleepWake-Up
Power Down
Watch Dog
Ignition “ON”Advance/
Overrun
VA = Load Cutout Signal
Sleep = Temporary Power Down of Control Unit
Wake-up = Activating the Control Unit
Watch Dog = Monitoring
Engine Off
Engine On
Engine Running
Terminal 15 “ON” VA up
VA Down
Terminal 15 “OFF”

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.