BMW 740iL Reparaturanleitung

Initial Print Date:3/02 Revision Date:Subject PageHydraulic Level Control System ...Air Suspensi

10Level Control SystemsRear Shocks With Load Dependent Module (LAD)E32/E34 Rear Shockwith LADE38 Rear Shock with LADPressureReservoir Connection LAD H

11Level Control SystemsLAD ModuleWith a high pressure applied to the control piston,the flow resistance is high and the damping forcewill be stiff.The

12Level Control SystemsCamber Warning Switch (E32 AND E34 Touring)The self-leveling suspension systems used in the E32 and the E34 Touring are equippe

13Level Control SystemsAir Suspension Systems (EHC)Purpose of the SystemAir Suspension systems were first introduced on the 1999 E39 Sportwagon. Sinc

14Level Control SystemsEHC System OverviewEHC I Single Axle Air Suspension E39/E53EHC II Dual Axle Air Suspension E531. Air Supply Unit2. Rear Axle

15Level Control SystemsSingle Axle EHC I System Components (E39/E53)The EHC system consists of the following components:• EHC Control Module• Air Spri

16Level Control SystemsThe control module incorporates two filters (slow/rapid) for processing the input signalsfrom the ride height sensors. Dependin

17Level Control SystemsAir SpringsThe air spring is made from a flexible rubber material. Itforms an air tight cavity which provides the calculatedsp

18Level Control SystemsAir Supply System (LVA)The air supply system is identified as the LVA in the diagnosis program and in the repairmanual. It is

19Level Control SystemsAir Supply System (LVA) OperationThe single stage piston compressor produces a maximum pressure of 13.5 Bar. The com-pressor is

2Level Control SystemsModel: Level Control Systems Production: E32 750iL 88-94 (Hydro-Pneumatic)E32 740iL 93-94E38 750iL 95-01E38 740iL 95-01E34 Tour

20Level Control Systems

21Level Control SystemsEHC System OperationA fully functional EHC system is controlled by one of three different modes of operation.The operation mode

22Level Control SystemsNormal Mode OperationOnce the rear lid is closed, KL 15 switched ON and the engine started, the system switch-es into the norm

23Level Control SystemsSpecial Operating Modes• Assembly Line Mode (New control module)The assembly line mode refers to control module manufacturing.

24Level Control SystemsEHC Service InformationDiagnosis/Coding• The EHC control module is connected to the diagnostic link. The EHC control moduleacti

25Level Control SystemsDISplus/GT-1 Service Functions ProgramThe Service Functions program of the DIS/MoDiC provides the Transport Mode activa-tion/de

26Level Control SystemsTIS Repair Manual InformationThe repair manual contains the following EHC specific sub-group repair information:• 00 General (g

27Level Control SystemsTwo Axle Air Suspension (E53 EHC II)Purpose of the SystemThe two axle air suspension system (EHC2) offers advantages over the

28Level Control SystemsSystem componentsThe X5 Two Axle Air Suspension System (EHC2) utilizes the air supply unit from EHCmounted in the luggage compa

29Level Control SystemsPneumatic Drain ValveThe Pneumatic Drain Valve is activated pneumatically by pressure from the control valve.This causes the dr

3Level Control SystemsLevel Control SystemsPurpose of the SystemThe primary function of Level Control Systems is to maintain the height of the vehicle

30Level Control SystemsCompressorCompressor operation is the same as in EHC with the following technical improvements:• Addition of a temperature sens

31Level Control SystemsThe pressure accumulator decreases the load on the compressor and significantly reducesthe time required for large changes in r

32Level Control SystemsRide Height SensorThe control unit obtains information about the ride height of the vehicle via a ride height sen-sor attached

33Level Control SystemsAir Suspension StrutRear Minor modifications were made to the rear axle air springs. The air springs and the dampersare configu

34Level Control SystemsSwitch AssemblyThe dash mounted switch assembly supplies a momentary switched ground to the EHC2Control Unit requesting a ride

35Level Control SystemsPrinciple of OperationRide Height Control OperationsIn addition to the automatic ride-height control system for payload compens

36Level Control SystemsThe various levels can be preselected while travelling. Changeover between ride levels iseffected at the speed threshold values

37Level Control SystemsIn addition to the LED indicator, the following text messages canbe displayed in the instrument cluster:•TTRRAAIILLEERR MMOODD

38Level Control SystemsAll control operations in advance / overrun mode are executed as long as pressure is avail-able in the accumulator. When the ac

39Level Control SystemsWorkshop HintsIf a threshold level is exceeded on all 4 wheels when the vehicle is stationary, the controlunit assumes that the

4Level Control SystemsHydropneumatic Rear Leveling SystemThis module pertains to the hydropneumatic rear suspension system with the engine dri-ven pis

40Level Control SystemsIf the fabric of the bellows is visible, then the bellows must be replaced.Upon completion of repair work, the air suspension s

41Level Control SystemsSingle Axle Air Suspension (E65/E66)Purpose of the SystemThe single axle air suspension system used on the the E65/E66 is a fur

42Level Control Systems

43Level Control SystemsComponents (E65/E66)Air Supply Unit (LVA)The air supply unit is located in the spare tire recess and consists of the following

44Level Control SystemsControl UnitThe EHC control module is located in the right rear luggage compartment area in the mod-ule carrier next to the bat

45Level Control SystemsAir SpringsAn identifying feature of the E65/E66 air spring is the internally guided air bellows. Internallyguided means that

46Level Control SystemsRide Height SensorThere are two ride height sensors, one for each rear wheel. The ride height sensor is actu-ated by a couplin

47Level Control SystemsControl Mode Flow ChartThe following chart demonstrates the control sequences of the E65/E66 with single axlerear air suspensio

48Level Control SystemsPrinciple of OperationControl Mode OverviewControl ModesOngoing control operations are not affected by transitions from one mod

49Level Control SystemsPost ModeThe Post-mode is adopted in order to compensate any inclination or to adjust the rideheight after driving and between

5Level Control SystemsSystem ComponentsThe system consists of the following components:• Tandem Hydraulic Pump• Oil Reservoir• Pressure Reservoir (2)•

50Level Control SystemsNormalThe normal mode is the starting point for the vehicle’s normal operating state. It is obtainedby way of the engine runni

51Level Control SystemsKerb (Curb) ModeThe Kerb mode prevents the inclination caused by the vehicle mounting an obstacle withine wheel from being comp

52Level Control SystemsLiftThe Lift mode is used to prevent control operations when a wheel is changed or duringwork on the vehicle while it is on a l

53Level Control SystemsOperating PrincipleInitialization/Reset PerformanceWhen the control unit is powered up after a reset (such as an undervoltage &

54Level Control SystemsSafety ConceptThe safety concept is intended to inhibit any system malfunction, particularly unintentionalcontrol operations, t

55Level Control SystemsWorkshop HintsRide Height MeasurementWhen checking vehicle ride height with EHC, measure from the lower edge of the wheelopenin

56Level Control SystemsReview Questions1. The EHC control module on the E65/E66 is connected to the Bus.2. List the operating modes that are specific

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

6Level Control SystemsTandem PumpThe tandem pump consists of a vane pump for power steering and a radial pump for self-leveling suspension. Both pumps

7Level Control SystemsOil ReservoirThe single reservoir stores fluid for both the self-leveling and power steering systems.Incorporated in the reservo

8Level Control SystemsPressure ReservoirsThe oil pressure reservoirs (2) on each strut incorporate a membrane and are nitrogen gasfilled. They are des

9Level Control SystemsControl ValveThe rotary control valve located on the rear suspension has three positions:• Raise• Level• LowerThe control lever