Volkswagen Self Study Program 331 – Variable Anti-roll Bars on the Touareg SSP-331-Variable-anti-roll-bars-on-Touareg

Service Training

Self-Study Programme 331

Variable Anti-roll Bars on the Touareg

Design and Function

The running gear is a key component of the
entire vehicle. It transmits all the forces acting
between the road surface and the body.
It therefore has a direct effect on driving comfort
and driving safety.

The best tuning for optimum off-road mobility,
however, requires soft suspension with low
damping factor and less rigid anti-roll bars. To
solve this conflict of requirements, ThyssenKrupp
has developed a variable anti-roll bar.

The Touareg is a sporty SUV off-road but also a
sporty, safe car on the road, with firm
suspension, stiff dampers and rigid anti-roll bars.

It consists of split anti-roll bars which are an
optimal compromise between dynamic handling
characteristics, driving comfort and off-road
mobility - it is a coupling that is also switchable
under load.

This self-study programme describes the design
and function of new developments.
The contents will not be updated.

2

Please always refer to the relevant Service Literature
for all inspection, adjustment and repair instructions.

S331_001

NEW Important

Note

Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4

Driving physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Block diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

General overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Design and function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

System overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Function diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32

Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

Test your knowledge. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3

Introduction

Conventional anti-roll bar

Spring damper

Subframe

Anti-roll bars improve cornering behaviour by
reducing body roll.

An anti-roll bar consists of a U-shaped tube.
The middle part of the anti-roll bar is secured to
the subframe by means of rubber-bush bearings
that allow rotary movement. It is also directly
attached to the spring dampers by means of a
coupling rod.

Rubber-bush

bearings

Anti-roll bar

Coupling rod

When the wheel on the outside of the corner
bounces, the anti-roll bar reduces the rebound
movement of the wheel on the other side of the
axle on the inside of the corner.

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4

Variable anti-roll bar

An off-road vehicle requires an extremely rigid
anti-roll bar on the road. This prevents extreme
body roll due to the high centre of gravity when
cornering at high speeds.

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Sporty, safe on-road handling

Off-road, anti-roll bars with low spring rates
allow more torsional twist on the axle.
This achieves continuous traction and high
driving comfort.

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Optimum off-road mobility with high driving comfort

Anti-roll bar arms

The variable anti-roll bar is a suspension system
for optimising on-road and off-road driving
characteristics.

Claw coupling

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A hydraulically operated claw coupling couples
and decouples the two anti-roll bar arms.

5

Driving physics

On-road driving

On-road, the anti-roll bar is coupled and extremely resistant to torsional twist (rigid). This allows sporty,
safe on-road handling.

Off-road driving

Off-road, the anti-roll bars are uncoupled. When the anti-roll bars are uncoupled, the wheels on one

axle are free to bounce and rebound independently of each other. This increases off-road mobility,
driving comfort and traction.

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6

Torsional twist

When the anti-roll bars are uncoupled, the torsional twist on an axle is increased by max. 60 mm.

+60 mm

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In the examples below, normal torsional twist has already been reached.
When the anti-roll bars are uncoupled, the axle can achieve an additional torsional twist of max. 60 mm
either on one side or as an aggregate on both sides.

60 mm

0

31 mm

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29 mm

Variable anti-roll bars are available for vehicles fitted with steel and air suspension.

7

Block diagram

Uncoupling an anti-roll bar

Claw coupling, front

axle anti-roll bar

Front axle anti-roll bar

uncoupling switch valve N399

Pressure

accumulator

Non-return valve

Pressure

chamber 1

Pressure

chamber 2

Claw coupling,

rear axle anti-roll bar

Pressure

chamber 1

Rear axle anti-roll bar

uncoupling switch valve N400

Hydraulic unit pressure

sensor for anti-roll bar

uncoupling G486

Pressure

chamber 2

Anti-roll bar

uncoupling

motor V326

Hydraulic supply

unit

Filter

Electric motor

Ventilation

Expansion tank

S331_036

8

Coupling an anti-roll bar

Claw coupling, front

axle anti-roll bar

Front axle anti-roll bar

uncoupling switch valve N399

Pressure

accumulator

Non-return valve

Pressure

chamber 1

Pressure

chamber 2

Claw coupling,

rear axle anti-roll bar

Pressure

chamber 1

Rear axle anti-roll bar

uncoupling switch valve N400

Hydraulic unit pressure

sensor for anti-roll bar

uncoupling G486

Pressure

chamber 2

Anti-roll bar

uncoupling

motor V326

Hydraulic supply

unit

Filter

Electric motor

Ventilation

Expansion tank

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9

General overview

Variable anti-roll bar and its components

The overall system of the variable anti-roll bar consists of three main components:

● the hydraulic supply unit

● the anti-roll bar control unit

● the variable anti-roll bars

Rear axle anti-roll bar

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Anti-roll bar control unit

Front axle anti-roll bar

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Hydraulic
supply unit

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10

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Function of the variable anti-roll bar

When the ignition is switched on, the variable anti-roll bar is functional.

Uncoupling by pressing the button

Only when

● the vehicle road speed is less

than 40 km/h,

● lateral acceleration is less than 0.5 g and

● the control unit is not in fault mode,

can the driver uncouple the anti-roll bars.

Function

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The opening pressure of the anti-roll bar is 110 bar. The coupling operation display in the dash panel
insert flashes until the opening pressure has been reached.

The rear axle anti-roll bar is uncoupled first, then the front axle.

When front axle uncoupling is completed, the coupling operation display appears continuously.

The pump motor continues to run throughout the entire operation and stops when a system pressure of
145 bar has been reached to charge the pressure accumulator.

If the driver presses the coupling button again or a system fault occurs, the uncoupling operation is
cancelled.

Only when the gearbox is switched to "low" will the anti-roll bar uncoupling motor switch on
automatically. The pressure accumulator will charge the system without the driver having to
press the button. The system can thus react very quickly if the driver presses the button to
uncouple the anti-roll bars.

11

Function

Coupling by pressing the button

For driving dynamic reasons, the front axle
anti-roll bar is coupled before the rear axle
anti-roll bar.

The anti-roll bar coupling operation is indicated
by the coupling operation display flashing in the
dash panel insert.
When the coupling operation is completed, the
associated display disappears from the dash
panel insert.

When the front axle is uncoupled and the pressure in the pressure accumulator is below 70 bar, the
coupling operation for the rear axle is delayed until the pressure reaches 70 bar again. This function
protects the pressure accumulator from destruction.

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The pump motor continues to run during the entire operation and stops when pressure in the system
reaches 110 bar.

Automatic coupling

The system couples the front and rear anti-roll bars automatically when

● the vehicle exceeds a road speed of 50 km/h,

● lateral acceleration exceeds 0.9 g at a road

speed below 35 km/h or

● lateral acceleration exceeds 0.7 g at a road

speed above 35 km/h.

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12

System pressures

Pressure Description

Function

70 bar Minimum

pressure

90 bar Minimum

pressure

110 bar System

pressure

145 bar Max. system

pressure

● To protect the pressure accumulator from destruction, pressure in

the system must be over 70 bar during the coupling operation.

● When the front axle is coupled and pressure in the pressure

accumulator is below 70 bar, the system delays coupling of the rear
axle until pressure reaches a minimum level of 70 bar.

● When the gearbox is switched to "low", the pressure accumulator is

recharged if the pressure drops below the minimum level of 90 bar.

● The anti-roll bar opening pressure is 110 bar.

● If the system pressure drops below 90 bar during the uncoupling

operation, the pump starts and builds up system pressure to
110 bar.

● The pump motor runs during the entire uncoupling operation and

stops when system pressure reaches 145 bar in order to charge the
pressure accumulator. This is monitored by the hydraulic unit
pressure sensor for anti-roll bar uncoupling.

● If pressure drops below 115 bar in uncoupled mode, the system is

recharged to 145 bar.

13

Design and function

Hydraulic supply unit

The hydraulic supply unit on the Touareg is
located behind the rear left side trim panel
above the rear wheel housing.

Pressure accumulator

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Expansion tank

The supply unit consists of a hydraulic pump
driven by an electric motor, an expansion tank, a
pressure accumulator, a pressure sensor and two
anti-roll bar switch valves.

Anti-roll bar

uncoupling motor

Pressure sensor

Anti-roll bar uncoupling

switch valves

Electric motor

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This supply unit allows the rear axle and front
axle anti-roll bars to be switched separately.

14

Anti-roll bar uncoupling switch valves N399 and N400

Switch element

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When the driver presses the anti-roll bar
uncoupling button, the switch valves N399 and
N400 are electrically operated.

The switch element connects the duct from the
pressure accumulator to the appropriate duct in
pressure chamber 1 of the related anti-roll bar.

Pressure chamber 1 Pressure chamber 2

Sleeve

The switch valves are designed to prevent leaks
almost completely. This is achieved by the gap
between the switch element and the sleeve
closing as a result of suspended particles in the
hydraulic fluid.
System pressure can thus be maintained over a
long period of time.

Pressure

accumulator

Anti-roll bar

Anti-roll bar

switch valve

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15

Design and function

Pressure accumulator

The pressure accumulator is a hydropneumatic
diaphragm unit. It accumulates hydraulic
pressure energy and supplies it on demand to
the hydraulic supply unit.

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The pressure accumulator is mounted directly on
the pump housing. It is divided into two

chambers by a diaphragm. The lower chamber
receives the hydraulic fluid which is pumped by
the anti-roll bar uncoupling motor.
The upper chamber is filled with nitrogen gas.
Incorporating compressible nitrogen gas into the
hydraulic circuit allows energy to be stored. This
means that gas and fluid must be physically
separated.

Nitrogen gas

Diaphragm

Hydraulic fluid

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16

Nitrogen gas

Diaphragm

Hydraulic fluid

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How it works

When the hydraulic fluid is pumped into the
pressure accumulator via the
non-return valve, pressure in the system rises in
relation to the volume of fluid pumped. The
nitrogen gas
is compressed and the volume of the gas
chamber diminishes. The fluid volume rises at the
same rate until the cut-off pressure is reached.
Pressure in the accumulator is maintained by the
non-return valve and is supplied to the
anti-roll bars via a duct.

Pressure accumulator

Anti-roll bar

uncoupling motor

To protect the pressure accumulator, pressure in the system must be over 70 bar during the
coupling operation.

Non-return valve

Hydraulic unit pressure

sensor for anti-roll bar

uncoupling

Electric motor

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17

Design and function

Hydraulic unit pressure sensor for anti-roll bar uncoupling G486

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S331_050

The hydraulic unit pressure sensor for anti-roll
bar uncoupling monitors system pressure over a
range of 0 bar to 250 bar.

Design

The sensor consists of the sensor electronics (b)
and a piezoelectronic element (a) which reacts to
the hydraulic fluid pressure.

The pressure accumulator is recharged if the
pressure drops below a minimum of 90 bar when
the anti-roll bars are uncoupled, or when the
anti-roll bars are coupled and the gearbox is
switched to "low".

ba

18

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1

How it works

The hydraulic fluid pressing on the piezoelectric
element changes the charge distribution in the
element.
Without the action of pressure, the charges have
an even distribution (1). If pressure starts to act,
the charges change their physical position (2).
This generates an electrical voltage.

The higher the pressure, the more the charges
are separated. The voltage rises. It is amplified

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by the electronic circuits and sent as a signal to
the anti-roll bar control unit.

2

The voltage intensity is therefore directly
proportional to the hydraulic pressure.

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19

Design and function

Anti-roll bar uncoupling motor V326

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Coupling piece flange

The anti-roll bar uncoupling motor is driven by
the electric motor via the coupling piece.

Oil flow in the pump

Coupling piece

It draws hydraulic fluid out of the expansion tank
and pumps it to the pressure accumulator via a
non-return valve.

To pressure accumulator

Gear wheels

Coupling

piece flange

20

Intake duct from

expansion tank

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Intake duct from

expansion tank

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To pressu re

accumulator

Pressure chamber

Housing wall

Gear wheels

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How it works

The anti-roll bar uncoupling motor is a gear
pump. The opposing rotary motion of the two
gear wheels pumps the hydraulic fluid along the
outside of the housing wall.

A definite volume of hydraulic fluid is taken in
depending on the volumetric space between the
teeth and the housing wall. This volume is then
pumped in the direction of rotation of the gear
wheel.

The two gear wheels intermesh in the middle.
The volumetric space becomes smaller and the
hydraulic fluid is pressed out of the volumetric
space. Pressure then rises in the pressure
chamber. When the pressure has risen
sufficiently, the non-return valve opens and the
hydraulic fluid is pumped to the pressure
accumulator.

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Volu m etric s p ace

21

Design and function

Expansion tank

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Connection for

vent line

S331_016

Connection for

supply line

Connection to

supply unit

The expansion tank is inserted onto the supply
unit and secured by a hose clamp. It is designed

to prevent the pump from running dry in any
driving situation.

There are two connections on top of the
expansion tank: one is for the vent line and the
other is for the supply line.

There is no min./max. marking. Oil level is
checked through the supply line using a modified
customary commercial plastic bottle (refer to the
"Service " section on page 33).

22

Electric motor

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S331_056

The electric motor is a direct-current motor with a
permanent magnet. It is also termed a
permanently excited collector motor.

Anti-roll bar control unit J742

The fitting location for the control unit is in the
luggage compartment under the spare wheel
cover.

It is inserted on end in a moulded foam packing
with the connector output pointing upwards.

The anti-roll bar control unit is connected to the
vehicle's drivetrain CAN databus.

It evaluates the following signals:

● system pressure

● switching state of the anti-roll bar

● anti-roll bar uncoupling button signal

Due to its linear characteristic curves, it is an
adaptable and readily controllable drive.

S331_010

It receives the following signals:

● road speed

● lateral acceleration

● gearbox mode (high or low)

The control unit sends a signal to the actuators
depending on the result of evaluation.

23

Design and function

Anti-roll bar

The key component of the variable anti-roll bar is
the hydraulically operated actuator. It is
positioned in the middle of the anti-roll bar.

Front axle anti-roll bar

Actuator

Anti-roll bar arm

The actuator contains a claw coupling which
couples and uncouples the anti-roll bar arms.

Anti-roll bar arm

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Rear axle anti-roll bar

Anti-roll bar arm

Actuator

Anti-roll bar arm

S331_082

24

Claw coupling

The hydraulically operated claw coupling
consists of input-side and output-side coupling
elements, a switching element, a fail-safe spring
and an anti-roll bar uncoupling sensor
positioned on the housing.

Closed coupling

Axial needle

bearing

Pressure
chamber 1

Input-side

coupling element

Pressure

chamber 2

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Fail-safe spring

Switching element

Open coupling

Left anti-roll

bar arm

Pressure

chamber 1

Anti-roll bar uncoupling sensor

Output-side

coupling element

Twist angle approx. 34°

S331_088

Right anti-roll

bar arm

Pressure

chamber 2

Magnetic pin in

switching element

25

Design and function

Switching element

Left anti-roll

bar arm

The switching element is free to move along its
axis. Its axial position is dependent on the
pressure applied and in its closed position, the
input-side and output-side coupling elements are
fully interlocked.

Input-side coupling

element (with right anti-roll

bar arm fixed)

Output-side coupling element (with left

anti-roll bar arm fixed to the housing)

Switching

element tongues

The switching element does not retract
completely and the two tongues overlap the
coupling elements at all times. This allows a
coupling operation in any driving situation.
In the figure above, the two switching element
tongues are depicted fully retracted from the
coupling elements. This is purely to show the
design of the switching element.

Right anti-roll

bar arm

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Switching element

26

Anti-roll bar uncoupling sensors G484 and G485

The "anti-roll bar coupled" switching position is
signalled when the anti-roll bar sensor contacts
the magnetic pin. The anti-roll bar uncoupling
sensor signal is required by the anti-roll bar
control unit to monitor the system.

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Fail-safe spring

The fail-safe spring is a coil spring which forces
the anti-roll bar closed if there are faults in the
hydraulic supply or electrical defects.

Anti-roll bar uncoupling button E484

The anti-roll bar uncoupling button is located
centrally on the centre console. It sends the signal
indicating the driver's command to couple or
uncouple the anti-roll bars to the anti-roll bar
control unit.

If the driver presses the button several times, the
coupling or uncoupling operation is cancelled.

An axial needle bearing is fitted between the
fail-safe spring and the switching element to
minimise wear.

If the button is pressed for longer than 30
seconds, this is detected as a system fault.
An entry is made in the control unit fault memory.
The anti-roll bars remain coupled.

The anti-roll bar uncoupling button is fitted with
an anti-roll bar uncoupling warning lamp.

Button on vehicle equipped with steel suspension Button on vehicle equipped with air suspension

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Anti-roll bar

uncoupling button

Anti-roll bar uncoupling

warning lamp

Anti-roll bar

uncoupling button

Anti-roll bar uncoupling

warning lamp

S331_013

27

Design and function

Anti-roll bar uncoupling warning lamp K221

Warning lamp

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Displays in the dash panel insert

The anti-roll bar uncoupling warning lamp K221
is located in the anti-roll bar uncoupling button
E484.

If the anti-roll bars are uncoupled, the display
appears continuously.

The warning lamp flashes during the coupling or
uncoupling operation.

The current anti-roll bar switching state is
displayed in the dash panel insert.

The symbols are different depending on the
vehicle's equipment.

On the Highline dash panel insert, the symbols
are displayed in pixel graphics; on the Premium
equipment level, they appear on a TFT screen.

Highline
equipment
level

28

Premium
equipment
level

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Uncoupling

The coupling operation display flashes for the
entire duration of the operation. When the
anti-roll bars are uncoupled, the coupling
operation display is continuously lit.

Coupling

The coupling operation display flashes for the
entire duration of the operation.
The display disappears only when the operation
is completed and the anti-roll bars are coupled.

Highline display

Coupling

opertion display

S331_078

Premium display

Gearbox mode

display

Coupling

operation display

S331_074

Gearbox mode

display

29

Design and function

Highline display

S331_076

Premium display

Flag

Fault display

Fault display

If a fault occurs during the uncoupling or
coupling operation, it is displayed by a flag.
At the same time, the fault display "System fault
workshop" appears.

It is no longer possible to uncouple the anti-roll
bars. The vehicle can still be driven.

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Flag

Flag

Fault display

30

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System overview

System overview

Sensors Actuators

K221 Anti-roll bar uncoupling warning

E484 Anti-roll bar uncoupling button

G484 Front axle anti-roll bar uncoupling

sensor

lamp

N399 Front axle anti-roll bar

uncoupling switch valve

G485 Rear axle anti-roll bar uncoupling

sensor

G486 Hydraulic unit pressure sensor

for anti-roll bar uncoupling

N400 Rear axle anti-roll bar

uncoupling switch valve

J742 Anti-roll bar control unit

V326 Anti-roll bar uncoupling motor

Gearbox mode, high or low

Road speed

Lateral acceleration

Drivetrain CAN data bus

J285 Dash panel insert

(gateway)

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31

Function diagram

Term . 30
Term. 15

S

S

S

S

G484

G485

K221

E484

J742

32

V326

A - Drivetrain CAN databus - Low

B - Drivetrain CAN databus - High

E484 Anti-roll bar uncoupling button

G484 Front axle anti-roll bar uncoupling sensor

G485 Rear axle anti-roll bar uncoupling sensor

G486 Hydraulic unit pressure sensor for anti-roll bar

uncoupling

J742 Anti-roll bar control unit

K221 Anti-roll bar uncoupling warning lamp

N400

N399

G486

N399 Front axle anti-roll bar uncoupling switch valve

N400 Rear axle anti-roll bar uncoupling switch valve

V326 Anti-roll bar uncoupling motor

Colour codes/key

= Input signal

= Output signal

= Positive

= Earth

= Drivetrain CAN databus

S331_026

Checking the oil level

Filler hole Plug

Service

The filler hole and plug for filling and checking
the oil level is located behind the left-side
tail-light.

Before the oil level can be checked, the left-side
tail-lamp must be removed and the system must
be depressurised, e.g. using the VAS 5051
Diagnosis Testing and Information System.

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Mark

Plastic bottle mark

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When checking the oil level or filling the system with oil, insert the plastic bottle hose into the filler hole
up to the mark.

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● The system may only be filled with central hydraulic system and power steering gear oil

G002000.

● Please read the instructions in ELSA (Electronic Service Information System) for setting the

mark, checking the oil level and filling the system with oil.

33

Service

Venting the system

Before the system can be vented, it must be
connected to the VAS 5051 Diagnosis Testing and
Information System, for example, and
depressurised.

Before venting, remove the dust caps and
connect a transparent plastic hose to the
ventilation nipple. As high pressures occur during
the ventilation operation, the hose must be
secured by a hose clamp.

Loosen the two ventilation nipples. The system
can then be vented according to the instructions
for using the VAS 5051 Diagnosis Testing and
Information System.

Ventilation nipple

Ventilation nipple

S331_142

Hose clamp

After ventilation is completed, tighten the nipples
and remove the plastic hose.

● Please read the instructions in the ELSA (Electronic Service Information System) carefully for

venting the system and for the size of the plastic hose required.

● Please remember to check the oil level before and after the venting operations.

● When working on the running gear, e.g. removing a suspension strut or tightening bolts on

rubber metal bearings, couple the anti-roll bars to prevent them from uncoupling due to
inadvertent switching and injuring service personnel, and to avoid damaging the running
gear.

Ventilation nipple

S331_144

Plastic hose

34

Test your knowledge

1. How are anti-roll bars uncoupled on the Touareg?

a) mechanically

b) hydraulically

2. When can the driver carry out an uncoupling command?

a) When the vehicle road speed is below 40 km/h and pressure in the pressure accumulator is below 70 bar

to prevent destroying the gas bubble in the pressure accumulator.

b) When the speed is above 50 km/h, lateral acceleration is greater than 0.7 g and the pump motor is

running.

c) When the vehicle road speed is below 40 km/h, lateral acceleration is less than 0.5 g and the control unit

is not in fault mode.

3. The claw coupling consists of two coupling elements, a switching element, a fail-safe spring and an
anti-roll bar uncoupling sensor. Why does the switching element not retract completely beyond the
overlap of the tongues when the anti-roll bar is uncoupled?

a) To allow coupling in every driving situation.

b) To avoid exceeding the defined maximum torsional twist of 60 mm.

c) So that the anti-roll uncoupling sensor can monitor the system in every situation.

1.) b; 2.) c; 3.) a

Answers

35

331

© VOLKSWAGEN AG, Wolfsburg, VK-21 Service Training

All rights reserved. Technical specifications subject to change without notice.

000.2811.47.20 Technical status 09/04

❀ This paper is produced from pulp

that has not been bleached with chlorine.