2003 BMW X5 Level suspension

30
Level Control Systems
Compressor
Compressor operation is the same as in EHC with the following technical improvements:
 Addition of a temperature sensor (Located on the compressor cylinder head)
Temperature sensor switches off the compressor at temperatures above 110
0C.
 Extended compressor ON time (180 seconds)
 Redesigned air drier to compensate for additional air volume.
Pressure Accumulator
The twin axle air suspension system now features a pressure accumulator which forms an
air accumulator valve unit in combination with the valve. The air accumulator valve unit is
located beneath the vehicle floorpan in the right-hand sill area.
Top: Air Drying
Bottom: Dissipation of water to airCompressor with Drier
Pressure Accumulator Unit which
includes:
Pressure Accumulator
Pressure Sensor
Valve Unit
Front

31
Level Control Systems
The pressure accumulator decreases the load on the compressor and significantly reduces
the time required for large changes in ride height.
The EHC 2 control module monitors system pressure via a pressure sensor mounted on
the accumulator. Normal system pressure is 15.7 +/- 0.7 bar. Minimum system pressure
is 9 bar.
The pressure accumulator's charge is sufficient to fill the four suspension struts once from
the Access position to the normal position and compensate for vehicle load up to maximum
gross weight.
Valve Unit
In the valve unit, four bellows valves and the pressure accumulator valve are activated.
The bellows valves and the pressure accumulator valve are solenoid valves which are
closed under spring pressure when de-energized.
Accumulator/Valve Unit
1. Air Lines
Yellow-Black Front
Red-Blue Rear
2. Pressure Accumulator
3. Connecting Cable
4. Pressure Sensor
5. Valve Unit
Valve Unit
1. Connections for Air Lines
2. Pressure Accumulator valve
Pneumatic Layout of Control Valve
1. Pressure Accumulator
2. Accumulator Pressure Sensor
3. Pressure Accumulator Valve
4. Bellows Valves
5. From the Air Supply Unit
NW Size of opening/tubing size in mm.

33
Level Control Systems
Air Suspension Strut
Rear
Minor modifications were made to the rear axle air springs. The air springs and the dampers
are configured separately at the rear axle.
Front
The air suspension replaces the steel suspension at the front axle, i.e. the spring bellows is
attached to the damper. The front air suspension strut and the impact absorber form a
complete unit.
Control Unit
The EHC2 Control Unit is located behind the glovebox adjacent to the General Module.
The connector is a black 54 pin connector.
Inputs received directly into the control unit are:
Ride Height Level Sensor (X4) Up and Down requests from the switch assy.
General Module (Load cutout signal) CAN Bus Inputs
K Bus Inputs Pressure Sensor
Compressor Temperature
O Ou
ut
tp
pu
ut
ts
s
i
in
nc
cl
lu
ud
de
e:
:
Air Unit Control (Activation) Front and Rear Axle Valves
LED’s for Switch Unit Compressor Relay
Pressure Accumulator
Air Suspension Strut
1. Auxiliary Spring
2. Air Bellows
3. Damper

35
Level Control Systems
Principle of Operation
Ride Height Control Operations
In addition to the automatic ride-height control system for payload compensation, the dri-
ver can set three different vehicle ride heights.
 Off-road (+25 mm), high ground clearance to a max. speed of 50 km/h
 Standard (0 mm), normal ride level
 Access (-35 mm), for entry and exit, loading and unloading to a max. speed of 35 km/h
or can be activated in Standard mode at road speeds < 25 km/h
The various heights are selected by scroll rocker. Light emitting diodes indicate the present
ride height setting.
Ride height can be adjusted from terminal 15 and with the doors closed. The hood and tail-
gate may be open.
The system also controls inclination automatically, like the single axle air suspension.
All control operations are executed without stopping at intermediate levels. The vehicle is
configured pneumatically in such a way that the front and rear axles can be lowered in par-
allel in any load situation. Depending on the load situation, either the front axle or the rear
axle is slightly quicker. On account of the different control speeds, a difference in height
between the two axles is possible during all control operations. If a max. permissible thresh-
old is exceeded, the quicker axle is stopped briefly.
The various levels can be preselected while travelling. Changeover between ride levels is
effected at the speed threshold values defined in the control unit. The control unit monitors
the change-over.
As soon as the driver sets a new target ride level by pressing a button or when a change-
over is initiated automatically by a specific driving condition, the LED for the current ride
level remains lit and the LED for the target ride level begins to flash.
When the new level is reached, the LED for the previous level goes out and the LED for the
new level reached stays lit permanently.

37
Level Control Systems
In addition to the LED indicator, the following text messages can
be displayed in the instrument cluster:
T TR
RA
AI
IL
LE
ER
R
M
MO
OD
DE
E
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.
R RI
ID
DE
E
H
HE
EI
IG
GH
HT
T
C
CO
ON
NT
TR
RO
OL
L
I
IN
NA
AC
CT
TI
IV
VE
E
Faults in the system and on the control unit which are only identified by the instrument
cluster, e.g. control unit disconnected
R RI
ID
DE
E
H
HE
EI
IG
GH
HT
T
C
CO
ON
NT
TR
RO
OL
L
I
IN
NA
AC
CT
TI
IV
VE
E
+
+
M
MA
AX
X.
.
6
60
0
k
km
m/
/h
h
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.

40
Level Control Systems
If the fabric of the bellows is visible, then the bellows must be replaced.
Upon completion of repair work, the air suspension system of the vehicle raised on the
workshop platform must be refilled with air via the diagnostics. The activation procedures
must also be repeated 6 times. This prevents the bellows from being folded incorrectly.
The vehicle must with be set down on its wheels when the suspension struts are depres-
surized!
Important Workshop Hint
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Areas on the air bellows which can possibly become leaky are the O-ring at the piston rod
and the seal carrier on the roll piston.
The connectors attached to all cables are identical to the connections on the single-axle air
suspension. 6 mm cable is used. The tightening torque is 3+
1 Nm throughout the system.
Special care must be taken when handling breakage-prone plastic parts of air suspension
elements.
Upon completion of repair work, Belt mode must be deactivated via the diagnostics. The
function LED on the button comes on. No text message appears in the instrument cluster.
The system is OK and ready for operation.

41
Level Control Systems
Single Axle Air Suspension (E65/E66)
Purpose of the System
The single axle air suspension system used on the the E65/E66 is a further enhancement
of the previous single axle air suspension system used on the the E39 and X5. The com-
ponents used are similar to the Single Axle EHC System on the E53. The E65/E66 Air sus-
pension consists of the following components:
 Air Supply System (LVA)
 Control Unit (EHC)
 Two Air Springs
 Two Ride Height Sensors
 CC Display/Telltale Icon

44
Level Control Systems
Control Unit
The EHC control module is located in the right rear luggage compartment area in the mod-
ule carrier next to the battery. On the E65/E66, the control module is connected to the K-
CAN S. The EHC control module receives the following information:
 Vehicle Ride Height
 Load Cutout Signal
 Terminal 15 ON/OFF
 Vehicle Speed
 Lateral Acceleration
 “Engine Running” Signal
 Flap Status (Doors/Trunk)
The Control unit decides on a case by
case basis whether a control opera-
tion is required in order to compen-
sate changes in load. It prevents
intervention in the case of other caus-
es. This makes it possible to adapt
the frequency, specified height, toler-
ance thresholds and battery load opti-
mally by means of the control opera-
tion to the relevant situation.
In addition to handling the self levelling
suspension, the control module moni-
tors the system components as well
as storing a displaying faults. The
control module has full diagnostic
capability.
The EHC module is a 26 pin module
with an ELO type connector. The
module is connected to the K CAN S.
The majority of the input messages
are from the K CAN S Bus.
EHC Module Location