2002 BMW X5 ehc

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

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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

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Level Control Systems
Ride Height Sensor
There are two ride height sensors, one for each rear wheel. The ride height sensor is actu-
ated by a coupling rod and sends a signal to the EHC control unit.
The sensor is a hall sensor which sends a DC Analog output voltage to the EHC module.
The voltage range is approximately .5 to 4.5 volts. The voltage increases with increasing
vehicle height and the nominal voltage at normal ride height is approximately 2.5 volts. The
right side rear sensor is a double sensor, the additional sensor is an input to the headlight
leveling systemand has it’s own power supply, ground and signal wires.
Check Control Messages
Control
UnitCauseVariable
Telltale IconCheck Control
MessageInformation in Control Display
EHC
Alive failure or
loss of function-
ality; transport
or belt mode setLevel Control
System failure“Level Control system failure”
Ground clearance and driving
comfort reduced. Avoid high
speed cornering. Have
checked by BMW Service as
soon as possible.
EHC
Level Control
System sensor
failure.Level Control
System Fault“Level Control System fault”
Possible reduction in driving
comfort. Have problem
checked by BMW Service.

48
Level Control Systems
Principle of Operation
Control Mode Overview
Control Modes
Ongoing control operations are not affected by transitions from one mode to another.
However, in the case of load cutout OFF, control operations are always concluded in order
to safeguard system deactivation. The control unit then sets the Sleep Mode.
Sleep
The vehicle is in Sleep mode at the latest when it has been parked for longer than 16 min-
utes with a door, hood or rear lid/hatch being operated or the terminal status changing.
This is the initial state of the control system. No control operation is being performed in
Sleep mode.
The control system goes into Pre-mode when a wake-up signal is received by the control
unit.
E39/E53 EHC I
(Single Axle)E65/E66
(single Axle)E53 EHC II
(Dual Axle)
SleepXXX
Wake-upX
PostX
PreXXX
Terminal 15 OnX
NormalXXX
DriveXXX
KerbXXX
CurveXXX
LiftXXX
TwistX
TrailerX
Off-RoadX
AccessX

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Level Control Systems
Kerb (Curb) Mode
The Kerb mode prevents the inclination caused by the vehicle mounting an obstacle with
ine wheel from being compensated. Compensation would cause a renewed inclination of
the vehicle and result in a renewed control operation after the vehicle comes off the obsta-
cle.
The Kerb Mode is activated when the height difference between the left and right sides of
the vehicle is > 32mm for the E65/E66 with single axle air suspension and >24mm for the
E39/E53 with single axle air suspension and lasts longer than 0.9s. Twisting (also over both
axles) > 45mm must occur for the E53 with twin axle air suspension.
There must be no speed signal present. The system switches from single wheel control to
axle control.
The Kerb mode is quit when the difference between the left and right sides of the vehicle is
< 28mm for the single axle air suspension and lasts longer than 0.9s when the speed is
greater than > 1km/h.
If the system switches from Kerb mode to Sleep mode, this status is stored in the
EEPROM.
If the vehicle is loaded or unloaded in Kerb mode, the mean value of the axle is calculated
by the control unit. The value is calculated in the control unit from the changes in ride level
of the spring travel on the left and right sides.
A change in ride level is initiated if the mean value of compression or rebound at the axle is
outside the tolerance band of +/- 10mm. The left and right sides of the vehicle are raised
or lowered in parallel. The height difference between the two sides is maintained.
Curve
Since rolling motions have a direct impact on the measured ride level, an unwanted control
operation would be initiated during longer instances of cornering with an appropriate roll
angle in spite of the slow filtering of the Drive mode. The control operations during corner-
ing would cause displacement of the air volume from the outer side to the inner side of the
curve. Once the curve is completed, this would produce an inclination which would result
in a further control operation. The Curve mode prevents this control operation whereby
when cornering is recognized slow filtering is stopped and a potential control operation that
has started is terminated.
The Curve mode is activated for the E65/E66 single axle EHC and for the E53 twin axle
suspension for a lateral acceleration of > 2m/s
2and deactivated at < 1.5 m/s2.
The lateral acceleration is recorded by the rotation rate sensor.

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Level Control Systems
Workshop Hints
Ride Height Measurement
When checking vehicle ride height with EHC, measure from the lower edge of the wheel
opening to the center of the wheel hub.
Diagnosis
Diagnostic items can be found in the “Control Unit Functions” path when using the DISplus
or GT-1. The functions available are Identifcation (ID page), Read/Clear Fault Memory, Read
Test Codes, Diagnosis Requests and Component Activation.
Service Functions
In the Diagnosis Program, there are numerous Service Functions that can be performed for
the E65/E66 EHC system. By entering into the “Function Selection” program and follow-
ing the “Chassis - Pneumatic Suspension” path all of the Service Functions are listed. The
Service functions include Ride-Level Offset, Transport Mode and Band Mode.

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Level Control Systems
Review Questions
1. The EHC control module on the E65/E66 is connected to the Bus.
2. List the operating modes that are specific to the E65/E66 Air Suspension System:
3. Why is the accumulator needed on the dual axle EHC system?
4. List the components specific to the Dual Axle EHC system:
5. Which 2 Buses system are connected to the EHC control module on the Dual Axle EHC
system?
6. What components are replaceable on the LVA?
7. What are the 3 possible ride height setting on the Dual Axle EHC system?
8. What type of sensor is used for ride height measurement?

9. How much pressure is in the rear air strut on the E66 when it is stored?
10. List the correct color for the air hoses on the EHC I system:
Left Right
11. The “Band Mode” is also known as
and
12. What operating modes are specific to the Dual Axle EHC system?
13. What is the maximum system pressure on the EHC I system (E39/E53)?
14. What is unique about the rear air struts on the E66?
15. What is the maximum air pressure of the air supply unit on the E53 with Dual Axle Air
Suspension?
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Level Control Systems