BMW 525I TOURING 1995 E39 Level Control System Manual

21
Level Control Systems
EHC System Operation
A fully functional EHC system is controlled by one of three different modes of operation.
The operation mode is selected by the control module based on current conditions provid-
ed by the monitored input signals. The main modes of operation are:
• Pre-Run/Post-Run Mode
 Normal Mode
 Tailgate Mode
Two special operating modes are also included in the control module programming.
 New/replacement mode(pre ZCS encoded). This mode provides basic operation.
 Transport Mode - Transport mode is set at the factory and raises the vehicle 30mm to
prevent vehicle damage during transportation. It must be deactivated with the DIS/
MoDiC prior to customer delivery.
Pre-Run / Post-Run Mode
The Pre-Run mode is activated when the vehicle is parked and the control module is in the
sleep mode. Opening a door or the tailgate initiates a system wake up and the control mod-
ule comes on-line.
The control module performs a self-check of the control electronics and sensors. If no fault
is found, the system will check the ride height and institute a rapid regulation if the height
varies by more than 40mm.

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.

24
Level Control Systems
EHC Service Information
Diagnosis/Coding
 The EHC control module is connected to the diagnostic link. The EHC control module
activates the fault display in the instrument cluster to alert the operator of the off-line sta-
tus of the system. The EHC control module stores up to three electrical/electronic
faults.
 Diagnosis/troubleshooting of EHC is carried out using the fault symptom troubleshoot-
ing program of the MoDiC or DIS. The EHC system has an extensive diagnosis program.
 Replacement control modules are shipped in the factory mode. The control modules
must be ZCS encoded using the DIS or MoDiC to activate the operating parameters.

25
Level Control Systems
DISplus/GT-1 Service Functions Program
The Service Functions program of the DIS/MoDiC provides the Transport Mode activa-
tion/deactivation and Ride Height Offset functions (see next page).
Once the transport mode has been released, or if the system requires left to right side
height adjustment, the ride height "OFFSET" must be carried out to ensure that the vehi-
cles suspension has a base ride height level starting point.
The "HEIGHT OFFSET" is adjusted using the DIS or MoDiC. The procedure is as follows:
 Place the vehicle on a level surface unloaded.
 Access the Height Offset program in the service function menu.
 Measure the base ride height from the lower edge of the wheel housing to the center of
the wheel hub.
 Check measured height against the specifications listed
 Use the DIS/MoDiC to correct the ride height if the value differs from the listed specifi-
cation.

26
Level Control Systems
TIS Repair Manual Information
The repair manual contains the following EHC specific sub-group repair information:
 00 General (general information, overview routing of pipes, tubes and components)
 12 Control and suspension system, rear (DIS referral, specific R&R procedures, etc.)
 13 Connecting Lines (specific R&R procedures)
 14 Electrical components (specific R&R procedures)
 22 Pump assembly (LVA) with container (LVA R&R procedure)
 90 Troubleshooting (system troubleshooting charts)
The troubleshooting charts provided an additional reference when used in conjunction with
the DIS program.
The following screen samples are from the TIS repair manual section.

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.

28
Level Control Systems
System components
The X5 Two Axle Air Suspension System (EHC2) utilizes the air supply unit from EHC
mounted in the luggage compartment, with the following components added or modified:
 Air Supply Unit (with redesigned compressor and drier)
 Pressure Accumulator
 Valve Unit
 Ride Height Sensor
 Air Suspension Strut
 Control Unit
 Switch Assembly
Air Supply Unit
As on vehicles with single axle air suspension, the air supply unit is located in the luggage
compartment under the spare wheel. As with the single axle air suspension, the auxiliary
tanks for the rear air spring bellows are located in the luggage compartment.
The air supply unit is configured similarly to the single axle air supply unit for the ride-height
control system of the E39, which is currently in production.
The functions are implemented by activating a compressor and various valves in the air
supply unit and on the air accumulator valve unit.
The maximum pressure of the air supply unit is 21 bar.
1. Air Supply Unit
2. Rear Axle Air Bellows
3. Ride Height Sensors
4. Pressure Accumulator/
Valve Unit
5. Front Axle Air Bellows
6. Control Unit
Pneumatic System of EHC2

29
Level Control Systems
Pneumatic Drain Valve
The Pneumatic Drain Valve is activated pneumatically by pressure from the control valve.
This causes the drain valve to open allowing the pressure supply line to vent to atmosphere.
This design allows for large air volumes to be discharged quickly and eliminates the need
for a solenoid valve with high current consumption.
The 21 bar pressure limiting valve is integrated in the drain valve.
Electric Pressure Relief Valve
The electrically activated pressure relief valve controls normal system pressure. The con-
trol valve performs this function in conjunction with the drain valve.
HIgh Pressure Vent Valve
The High Pressure Vent Valve serves as a comfort valve and is used to release system pres-
sure after the accumulator has closed and the compressor is still running. When the high
pressure vent valve has opened the compressor can be stopped quietly.
Air Drier
In the air drier, the air which is drawn in passes over a water absorptive filter material in the
form of filter nodules which extract moisture from the air. As long as the air contains more
moisture than the filter material, the individual nodules absorb and accumulate the mois-
ture. When the air flows back, it is drier than the filter material, with the result that the air is
re-humidified and the moisture is discharged into the open air. The maximum
water storage capacity of the filter is 30 g.
1. Pneumatic Drain Valve
2. Electric Pilot Control Valve
3. High Pressure Vent Valve
4. Air Drier
5. Compressor
6. Sintered filter
7. To Pressure Accumulator/Valve Unit NW Size of
opening/tubing in mm.
Air Supply Unit

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