tailgate BMW 525I TOURING 1989 E34 Level Control System Manual

15
Level Control Systems
Single Axle EHC I System Components (E39/E53)
The EHC system consists of the following components:
 EHC Control Module
 Air Springs (2) with Air Reservoirs
 Rear Axle Level Sensors
 Encapsulated Air Supply (LVA)
 Warning Indicator
Control Module
The Control Module is mounted in the module carrier box in the luggage compartment on
the right side. It contains the processing electronics and final stages for operation of the
EHC system.
The control module receives the following inputs for its processing functions:
 KL 30 & 31 (Power/Ground)
 KL 15
 Left & Right Ride Height Sensors
 K Bus for;
- Vehicle speed
- Engine running
- Door/tailgate - open/closed
E39 Features 06
EHC Module (E39)

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Level Control Systems
The control module incorporates two filters (slow/rapid) for processing the input signals
from the ride height sensors. Depending on the operating mode, either the slow or rapid fil-
ter is used to check the need for a regulating sequence.
The slow filter is used during the normal operation mode to prevent normal suspension trav-
el from causing the system to make adjustments.
The rapid filter is used during the pre-run and tailgate (LID) modes to ensure that the sus-
pension is adjusted quickly while the vehicle is being loaded or checked prior to operation.

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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.

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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 .