ESP BMW X5 2000 E53 Level Control System Manual

22
Level Control Systems
Normal Mode Operation
Once the rear lid is closed, KL 15 switched ON and the engine started, the system switch-
es into the normal operation mode. In the normal mode, the control module will constantly
monitor the input signals from the ride height sensors and will activate a correction if the
ride height deviates by at least 10mm.
Tailgate Operating Mode
The tailgate operating mode is activated if the gate is opened with KL - 15 On and the
engine running. The difference between this mode and the normal operating mode is the
response time is rapid instead of slow .

23
Level Control Systems
Special Operating Modes
Assembly Line Mode (New control module)
The assembly line mode refers to control module manufacturing. New control modules
are stored in a deactivated state. The control programming is not active and must first
be ZCS encoded.
After installing a replacement control module, it must be coded using the DIS or MoDiC.
The instrument cluster fault display will remain illuminated until the control module is
coded.
Transport Mode
The vehicle rolls off the factory assembly line with the EHC control module in the trans-
port mode. The transport mode inflates the air springs to a higher position (approx.
30mm higher) than the normal mode in order to avoid damage during transit.
The system will not respond to any inputs that would alter the height of the vehicle. The
fault indicator (base cluster) is illuminated or instrument cluster matrix display (high clus-
ter) provides the message “Leveling System” to draw attention to the transport mode
setting.
The Service Functions section of the diagnosis program is used to activate/deactivate
the transport mode. Once the transport mode is deactivated, check the vehicle Ride
Height Offset making sure the vehicle rear axle height is to specification.
Control Interrupts
Cornering
To prevent unnecessary suspension adjustments while driving through corners, a “control
interrupt” is built into the system. Above 30MPH the control module monitors the left/right
ride height sensors for a difference of 30mm. Exceeding this difference will put the system
into a control interrupt and no adjustment will take place. The control interrupt last for a
duration of 5 minutes.
Vehicle Lifting
The ride height control is interrupted when the vehicle is raised on a lift or with a jack. The
system monitors the ride height sensor inputs and when the height limit of 90 mm is
exceeded, the control is switched OFF until the vehicle is lowered again.

27
Level Control Systems
Two Axle Air Suspension (E53 EHC II)
Purpose of the System
The two axle air suspension system (EHC2) offers advantages over the single-axle air sus-
pension with respect to ride comfort and off-road capability.
Lowering the entire body makes it easier to enter, exit, load and unload the vehicle.
The vehicle's off-road capability was improved by providing the possibility for increasing the
ground clearance of the body.
The driver can now choose between three different ride levels which can be set with a rock-
er switch, as required. Automatic ride-height control for payload compensation and
automatic inclination compensation continue to be fitted.
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The automatic payload compensation facility for the single-axle air suspension did not per-
mit driver control. The driver could not actively control the system to make it easier to enter
and exit or load the vehicle.
Ride level was compensated via the rear axle only.
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The new system allows the ride-height control system to be controlled actively by the dri-
ver.
The twin axle air suspension allows both axles to be lowered evenly and in parallel.
As a result, it is easier for the occupants to enter, exit, load and unload the vehicle.
On the E39, the load of the complete rear axle was born for the first time by air suspension
in combination with the optional ride height control system. The system was controlled
automatically under all operation conditions, and there was no possibility for driver inter-
vention on the X5, the rear axle previously had single axle air suspension only. The air sup-
ply unit and the control unit were adopted from the E39. The air springs were adapted to
the X5.
There is a standard version and a sports version.
The ride-height control system (EHC) was supplied as standard in combination with the
M62 engine and is available as an optional extra in combination with the M54 engine.
EHC2 is optional on both the M62 and M54 versions of the X5 and not available on the
4.6is X5.

37
Level Control Systems
In addition to the LED indicator, the following text messages can
be displayed in the instrument cluster:
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RA
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A coupled trailer is identified via the trailer connector. To avoid damaging the trailer and
the vehicle, changes of vehicle level are generally avoided. The standard level is "frozen."
If the trailer is coupled at a level other than the Standard level, the vehicle ride level is
not changed to Standard unless a button is pressed or the speed threshold for auto-
matic change-over is reached. The standard level is then "frozen" until the trailer con-
nector is disconnected.
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Faults in the system and on the control unit which are only identified by the instrument
cluster, e.g. control unit disconnected
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For safety-critical faults (vehicle is too high or at inclination)
Control Modes
Sleep mode
If the vehicle is parked, it enters Sleep mode after 16 minutes. No further control opera-
tions are executed. A "watch dog" wakes up the control unit for a few minutes every 6
hours (wakeup mode) in order to compensate for possible inclination of the vehicle. (Vehicle
height may only be corrected once as air supply unit only operates with engine running.)
Wake-up
In wake-up mode, the control unit is woken up for a set period of time in order to com-
pensate for possible inclination of the vehicle. Inclination of the vehicle can be caused by
large temperature differences or by minor leaks. Adjustments to the front and rear axles
ensure that the vehicle is visually level. To minimize power consumption, the vehicle is low-
ered only. The nominal level of the lowest wheel serves as the nominal level for all other
wheels. The lowest nominal level to which the vehicle is lowered is the Access level (-35
mm).
Exception:if the vehicle is parked at Access level, the vehicle is lowered to max. -50 mm
in wake-up mode. If the vehicle is parked for a prolonged period of time and there is a leak
in the system, further loss of pressure does not produce a change of ride level since the
weight of the body is born by the auxiliary suspension and the residual tire pressure.
Advance /Overrun
When the vehicle is woken out of sleep mode by the load-cutout signal (VA), it normally
enters advance / overrun mode. Since the engine is not (no longer) running in this mode,
however, there are restrictions on the control operations that can be performed in order to
conserve the battery. Ride level compensation is restricted to tolerance ranges of 20 mm
and 25 mm in the up and down directions respectively. This serves to reduce the frequen-
cy of control operations.

50
Level Control Systems
Normal
The normal mode is the starting point for the vehicle’s normal operating state. It is obtained
by way of the engine running signal.
Ride level compensation, changing the vehicle’s ride height and filling the accumulator are
possible. The compressor starts up as required.
A narrower tolerance band than that in Pre-mode cab be used because the battery capac-
ity does not have to be protected. The fast filter is used with a narrow tolerance band of
+/- 10mm. In this way, ride level compensation takes place outside a narrow band of 10+/-
10mm. The faster filter allows the system to respond immediately to changes in ride level.
Evaluation and control are performed separately for each wheel.
When a speed signal is recognized, the control unit switches into Drive mode. When the
vehicle is stopped, the control unit remains in Drive mode. The system switches back into
Normal mode when a door or the boot (trunk) lid is also opened. If none of the doors or
the boot lid is opened, the vehicle cannot be loaded or unloaded.
This prevents a control operation happening when the vehicle (for example) is stopped at
traffic lights and the ride height is above the mean axle due to the pitching motion on the
rear axle.
Drive
The Drive mode is activated for E39/E53 single axle air suspension when a speed signal of
>4km/h is recognized. The Drive mode is recognized from >1km/h for the E65/E66 single
axle air suspension and for the E53 twin-axle air suspension system.
Low pass filters are used. In this way, only changes in ride height over a prolonged period
of time (1000 seconds) are corrected. These are merely the changes in ride height, caused
by vehicle compression and a reduction in vehicle mass due to fuel consumption. The high
pass (fast) filter is used during the control operation. The slow filters are recognized at the
end of the control operation. The slow filters are re-initialized at the end of the control oper-
ation. The markedly dynamic height signals caused by uneven road surfaces are filtered
out.

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.