SERVICE BULLETIN
SB1323
ADDRESSEES

: ABC Customer Care and Parts Source
Owners and operators of coaches equipped with electronic
controlled air suspension (ELC)

VEHICLE MODEL

: TD925US, TDX25US

MANUAL SECTION

: 3.6 Air suspension – Control system

BULLETIN TYPE

: Service Information

DATE

: March 18th, 2016

SUBJECT

: Introduction to electronic controlled air suspension
(ELC)

TERMS & CONDITIONS

: -

1. APPLICATION:
Following double-deck busses are fitted with an electronic controlled air suspension (ELC):
Model
TD925US
TDX25US

VIN
42780, 42846Æ42888, 42890Æ42891, 42920Æ…
42801Æ…

2. SYSTEM OVERVIEW
The electronic controlled air suspension maintains the ride height by using an electronic control
unit (ECU), height sensors, pressure sensors and solenoid valve blocks. The ECU uses the
information of the height sensors and the pressure sensors to determine the proper vehicle ride
height. If necessary, the ECU will change the pressure within the air bags by actuating
specified solenoids in the valve blocks.

3. BENEFITS
•
•
•
•

Less air consumption
Easy installation
High system flexibility (kneeling, lowering, raising, …)
Diagnostics capabilities

4. DASHBOARD DISPLAY MESSAGES
Symbol

Message

ELC system fault

ELC correct electrically supplied by the towing vehicle

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Symbol

Message
Kneeling system switched on

Raising system switched on

Lowering system switched on

Trailing axle unloading system activated

Axle overload (1 stands for axle 1) (optional)

5. DASHBOARD SWITCHES
Symbol

Message

To raise/lower air suspension from ride height (if present)

To switch on limited lowering system (if present)

To kneel vehicle

To switch on trailing axle unloading system

6. DRIVER’S INSTRUCTIONS
Refer to the operating manual of your vehicle.

7. PRECAUTION WHEN WORKING ON VEHICLES WITH ELC
Switch off the electronic controlled air suspension (ELC) before carry out works at components
located underneath the vehicle or before working in the wheel housing.

WARNING!
Failure to switch off the ELC system can cause dangerous situations due to
"unexpected" movements of the body, as well as damage to the vehicle.
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WARNING!
Body will lower beyond normal ride height, if air is depleted from the air bags.
Make sure no object or person gets trapped under the body edge or between a
wheel housing and a wheel.

8. TO SWITCH OFF ELC
Step

1
2

Action
Shut off the engine.
Switch off the vehicle ignition and prevent somebody from switching on the ignition
again by using the safety switch of figure 1.

7.1 Safety switch to prevent vehicle ignition from being switched on
With this safety switch you can prevent someone from switching on (intentionally or
unintentionally) the vehicle ignition while you are working on the vehicle (e.g. in case of
working underneath the vehicle or in the wheel housing during which the electronic controlled
air suspension (ELC) should not be activated).

Figure 1: Safety switch on the control panel in the
engine compartment (photo shows control panel of a
TD925/TDX25 vehicle)

7.2 To activate safety system
Step

1
2

Action
Switch off the vehicle ignition
Press the safety switch and equip it with a key lock.
It is now impossible to switch on the vehicle ignition.

Figure 2: Positions of safety switch
A Normal position
B Safety system activated

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9. IDENTIFICATION OF ELC COMPONENTS
Denomination
Electronic control unit (ECU)
•
•
•
•

Monitors the input signals and compares the
signals with the values stored in the ECU.
Activates the solenoid valves in the various
valve blocks to adjust the ride height
Monitors the function of all components and
stores information about errors
Stores preset levels (normal, lower, raise)

Figure

Figure 3

Height sensors
A height sensor provides the ECU with a chassis
height signal.

Figure 4

Solenoid valve blocks
Each valve block contains several solenoid
valves which are actuated by the ECU. The
solenoid valves convert the voltage into a
pressurizing or venting process which either
increases or reduces the air volume in the air
bags. If not activated, the valves are closed and
maintain the air bags volume.
•
•

Figure 5

Front-axle and trailing-axle valve block
(Figure 5)
Drive-axle valve block (Figure 6)

Figure 6

Pressure sensors
A pressure sensor provides the ECU with an air
bag pressure signal.

Figure 7

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10. STRUCTURE OF ELC:

Figure 8: Structure of ELC on
a three axle vehicle

Number in
figure 8

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

Explanation

Air spring
Test fitting of front-axle left air spring
Test fitting of front-axle right air spring
Height sensor
Front-axle valve block
Pressure sensor
Electronic control unit (ECU)
Pressure sensor of drive-axle service brakes tank
Pressure sensor of front-axle brakes tank
Pressure sensor of trailing-axle brakes tank
Pressure sensor of accessories tank
Test fitting of drive-axle left air spring
Test fitting of drive-axle right air spring
Drive-axle valve block
Test fitting of trailing-axle left air spring
Test fitting of trailing-axle right air spring
Trailing-axle valve block
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11. "NEO GREEN" DIAGNOSTIC SOFTWARE
This software is necessary:
• to read and/or erase the fault memory;
• to adjust the air-spring height;
• to display the parameters;
• to calibrate a new electronic control unit (ECU);
• to calibrate a new height sensor;
• to calibrate a new pressure sensor.
Ordering number for CD-ROM with “NEO” software: VH11479100
Refer to chapter 3.6 of your maintenance manual for installation instructions.

12. TO READ AND ERASE FAULT MEMORY OF ECU
Refer to chapter 3.6 of your maintenance manual.

13. TO ADJUST AIR SPRING HEIGHT
Refer to chapter 3.6 of your maintenance manual.

14. TO DISPLAY PARAMETERS
Refer to chapter 3.6 of your maintenance manual.

15. COMPONENT REPLACEMENT
•
•
•

Park the vehicle on a level surface
Block the wheels to prevent the vehicle from moving.
Release all air from the suspension system before removing any components. Pressurized
air can cause serious personal injury.

14.1 To calibrate a new ECU
The ECU should be calibrated after replacement by using the “NEO” software. Refer to
chapter 3.6 of your maintenance manual for instructions.
14.2 To calibrate a new height sensor
The height sensor should be calibrated after replacement by using the “NEO” software.
Refer to chapter 3.6 of your maintenance manual for instructions.
14.3 To calibrate a new pressure sensor
The pressure sensor should be calibrated after replacement by using the “NEO” software.
Refer to chapter 3.6 of your maintenance manual for instructions.

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16. TO TOW A VEHICLE EQUIPPED WITH ELC
Refer to chapter 7 of your operating manual or chapter 1.1 of your maintenance manual for
complete instructions.
The ECU of the ELC system must be supplied with electric power during towing. For that the
vehicle is equipped with connecting sockets at the front and rear to which an electric supply of
12 to 24Vdc must be connected.

Figure 9: ELC connecting socket behind
front bumper of TD925US/TDX25US

Figure 10: ELC connecting socket in
engine compartment of TD925/TDX25US

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INFORMATION HANDLING:
Important supplements to and modifications of the technical information not yet included in the Van
Hool manuals are communicated by means of Service Bulletins.

VAN HOOL CUSTOMER PORTAL:
Consult the Van Hool customer portal for the latest service documentation. Beside the
maintenance manual, you will also find the operating manual and the spare parts catalogue of your
vehicle on the customer portal. The customer portal is accessible through www.vanhool.be, and
only with a code (password) from Van Hool. If you do not have a password yet, request it by using
the link on the Van Hool website.

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