motion of the occupants.

Belt Reel

Belt Retractor Shaft

Toothed
Segments

Metal Bands

The amount of force that the safety belts can apply to
the occupants is limited. If this force is exceeded, the
belt retractor shaft and a belt winder allow controlled
unreeling of the safety belt. The force is distributed as
follows:

Locking
Mechanism
Support Ring
Toothed
Segments

1. From the safety belt reel through the retractor shaft
to the locking mechanism. The belt retractor shaft,
which is designed as a torsion bar, begins to rotate.

605_059

2. From the belt reel to the locking mechanism through
the toothed segment, support ring and metal bands.
The metal bands are connected to the support ring
and the locking mechanism. The metal bands are
retracted.
Depending on impact severity and longitudinal seating
position, the Airbag Control Module J234 activates the
Belt Force Limiter Igniters G551 and G552. The gas
pressure displaces the piston and causes the control
ring to rotate. This displaces the retaining ring and
disengages the toothed segments from the support
ring. The belt winder decouples. The torsion bar now
counteracts the safety belt force.

605_061

605_063

To provide maximum protection, the belt tensioning
function, the belt force limiting function and the front
airbags are coordinated. The belt force limiter igniters
are not activated in the event of a side impact or rear
collision.

Belt Reel

Control Ring

Support Ring

Retaining Ring

Retaining Ring
Toothed Segments

Belt Reel

Belt Retractor Shaft

Toothed Segments

Locking Mechanism

Support Ring

Metal Bands

Metal Bands

Control Ring

Locking Mechanism

Piston
605_062

Igniter

605_060

23

Passive Systems
Roll-Over Protection System

Function
In the resting state, the Roll Over Protection Solenoids
N309 and N310 are de-energized and hold the roll-over
protection system in a retracted position by means of
a hook. When the solenoids are energized this hook is
released, allowing the rollover protection elements to
raise.

Several Audi models, such as the Audi R8 Spyder, have
special mechanically operated roll-over protection
systems on account of their body design. When
activated, the roll-over protection system works in
combination with the A pillars to create a safety zone for
the occupants.

The springs raise the roll-over protection bars in
approximately 0.25 seconds.

A sensor for detecting an imminent roll-over is
integrated in the Airbag Control Module. This sensor,
together with other sensors built into the control
module, determine the severity of the impact. If a
rollover is detected, both the roll-over protection system
and the safety belt tensioners will be activated.

When deploying, a locking rail engages after
approximately 6.7 in (170 mm) of travel. This keeps the
roll-over protection bars extended. For service, the rollover bars can be mechanically unlocked and moved back
into their starting position.

As a safety precaution, the roll-over protection system is
also activated in the event of a strong head-on collision,
side-impact collision or rear collision as soon as a safety
belt tensioner or airbag deploys.

Release Lever

Locking
Rail

Spring
Toothed
Segment

Hook
Roll-over Protection Solenoid

24

605_064

Passive Systems
Sensors
Seat Occupant Sensor
Depending on model and trim, different seat occupant
sensors are used.
The Front Passenger Seat Occupant Sensor G128 is a
plastic film with eight pressure sensors. The resistance
of the individual sensors changes under load. The system
recognizes an occupied seating position only if two
pressure sensors are triggered simultaneously.
The seat foam molding is recessed to assure that the
G128 is installed in the correct position.
Airbag Control Module J234 uses the signals from the seat
occupant sensor and belt lock switch to determine if:

• A person is in the seat
• The safety belt is fastened

605_065

Examples:
Multi-Contour Sensor G128

Normal and Sport Seat Sensor G128

605_066

!

605_067

Note
This system is found only on earlier models

25

Passive Systems
Seat Position Detection
Seat Position Sensors G553 and G554 are located on
driver and passenger seat rails of several models. These
are Hall sensors. Based on the power consumption of
the seat position sensors, Airbag Control Module J234
detects whether the seats are in the front third or in
the rear two thirds of the seat adjustment range. The
Airbag Control Module uses this information to correctly
time the adaptability of the belt force limiters and the
front airbags.
If the seat is in the front third of its adjustment
range, J234 can activate the Adaptive Airbag Igniter 2
earlier than if the seat was in the rear two thirds of its
adjustment range.

Early ignition of the second airbag igniter allows airbag
deployment adaptation so that occupants with a small
body mass plunge into the airbag in a controlled manner.
Driver Belt Force Limiter G551 and Front Passenger
Belt Force Limiter G552 are also activated early. As a
result, the restraint systems are adapted to the accident
situation and seat position.
As always, a properly adjusted seat, correct seating
position and a correctly fastened safety belt are the first
steps to effective occupant protection.

Seat in "Back" Position

Seat Rail on Seat

The seat position detection sensors are installed on the
seat rail towards the center of the vehicle.
If the seat position detection sensor is above the seat
rail, J234 will determine that the seat is in the “back”
position.

Seat Position Sensor
Seat Rail on Vehicle

605_068

Seat in "Front" Position

Seat Rail on Seat

If the seat is pushed forwards and the seat position
sensor moves beyond the seat rail, the J234 will
determine that the seat is in the “front” position.

Seat Position Sensor
Seat Rail on Vehicle
605_069

26

Passive Systems
Safety Belt Reminder
Front Safety Belt Reminder
If the front occupants are not wearing their safety belts,
the Safety Belt Indicator Lamp K19 will illuminate after
the ignition is switched on.
The Safety Belt Indicator Lamp K19 illuminates if the
driver and/or passenger has not fastened his/her safety
belt. When the vehicle exceeds 15.5 mph (25 kph), an
acoustic warning will sound.
If the acoustic warning starts and the vehicle decelerates
to a speed of less than 3 mph (5 kph) within the first 30
seconds, the acoustic warning will stop.

If the vehicle's speed increases again to above 15.5 mph
(25 kph) , the acoustic warning resumes. If 30 seconds
have elapsed since the acoustic warning started, the
acoustic warning does not stop until the safety belts are
fastened.
The total duration of the acoustic warning is limited to
126 seconds. The acoustic warning also varies in volume
and frequency. The values below can vary depending on
model type and model year.

Front Safety Belts Not Fastened Warning

Terminal 15
Visual
Warning
Speed

On
Off
Active
Off
> 25 kph
< 5 kph

Audible
Warning

< 30 sec.

Active
Off

< 30 sec.

Approx. 96 sec.

605_070

27

Market-Specific Special Features
Occupation Protection Systems For Specific Markets
Vehicles can be equipped with other systems to meet the statutory and specific requirements of several countries.

Roll-Over Protection Bar System
Depending on the actual specifications, two additional
sensors are integrated Airbag Control Module J234
for rollover detection. ABS Control Module J104 reads
this additional information to provide higher rollover
detection sensitivity.

The airbag control module does not necessarily require
this information. It has the ability to independently
detect a rollover. If a rollover is detected, the belt
tensioners and the head/curtain airbags are deployed.

Knee Airbags
Knee airbags are optional on some models. They
provide for additional protection upon vehicle
deceleration. On the driver’s side, the knee airbag
is located in the footwell trim below the dash panel.
On the passenger’s side, the knee airbag is located
behind the glove compartment flap. The knee airbags
are activated in combination with the front airbags.
Hybrid gas generators are used for inflation.

View Looking into the Dash Panel

Airbag

Gas Generator

28

605_073

Market-Specific Special Features
Passenger Front Airbag
Adaptive Passenger Side Gas Generator
A hybrid gas generator with two pyrotechnic propellant
charges for inflation the airbag may be used depending on
country specifications.
The adaptability function of the passenger airbag module
is identical to the driver side airbag module and is
described earlier in this Self-Study Program.

Rupture Disc 1

Depending on the accident situation, the Airbag Control
Module J234 determines the interval at which the Front
Passenger Airbag Igniter 2 N132 is ignited after the
Front Passenger Airbag Igniter 1 N131.

Rupture Disc 3
Priming Charge 1
Propellant Charge 2

Igniter 2

Rupture Disc 2
Igniter 1

Propellant Charge 1

605_074

Active Head Restraint
Release Lever

If Airbag Control Module J234 detects a rear collision
that meets deployment conditions, the head restraints
on the front seats and safety belt tensioners are
activated. When the airbag control module energizes
Driver/Passenger Active Head Restraint Igniter N419 and
N420, the metal core is drawn into the solenoid coil. The
hook can no longer support itself on the metal core and
releases the front part of the head restraint.

Locking Device
Hook
Active Head Restraint Igniter
Metal Core

The hook moves approximately 2 in (50 mm) forwards
and approximately 3/4 in (20 mm) upwards. A locking
device prevents the front part of the head restraint from
pushing back into its starting position.

Spring

End Position
Starting Positions

Resetting the Active Head Restraint
The active head restraints can be reset. The release
lever releases the lock and allows the extended part of
the head restraint to be pushed back again. Refer to
ElsaWeb for specific model information.

605_090
29

Passenger Occupant Detection System
Passenger Side Seat Occupant Sensor
In several markets, the passenger seat is equipped with a
special seat occupant recognition system. Airbag Control
Module J234 can recognize two conditions:
1. Seat not occupied or child seat installed.

This determines whether the passenger front airbag and
passenger knee airbag are activated or deactivated. If
the components are deactivated, the Front Passenger
Airbag -Disabled- Indicator Lamp K145 illuminates to
inform the occupants.

2. Seat occupied by an adult.

Dielectric

Capacitive Front Passenger Seat
Occupant Sensor
In some Audi vehicles, the Passenger Occupant Detection
System Pressure Sensor G452 is now a capacitive sensor.
The capacitor is made of two plates (electrodes) and
an insulator (dielectric), sandwiched between the two
plates. When voltage is applied to one of the electrodes
and the other electrode is connected to the battery's
negative terminal, the capacitor begins to accumulate
energy. The capacitance of a capacitor can be altered by
varying the size of the electrode plate or the dielectric.

605_075

Function
With this seat occupant recognition system, the first
electrode plate is G452 and the second electrode plate
is the vehicle chassis. The size of these components is
not variable. The dielectric consists of the seat cover,
the atmosphere and the trim parts. These components
are the variable. When an adult is seated in the
passenger seat, the dielectric between the seat mat
and the body of the vehicle changes due to the person's
fluid content. The capacitance changes accordingly.

Electrode

If a child seat is placed on the passenger seat, the
dielectric and capacitance changes again. The change
in capacitance is much less than an adult.

Sensor G452

30

605_077

Passenger Occupant Detection Sysytem
Installation Position
Passenger Occupant Detection System Pressure Sensor
G452 is integrated in the seat cover above the seat
cushion. There are different seat types and also different
seat occupant sensors.

G452

605_076

Passenger Occupant Detection System Control Module J706
G452 is connected to J706 by a coaxial cable. J706
is in charge for performing the measurements that
determine seat occupant recognition. It detects the
change in the capacitance of the seat occupant sensor
G452 and can determine if the seat is vacant, has a child
seat or is occupied by an adult. The capacitance of the
seat occupant sensor is measured regularly by the seat
occupant recognition control module.

Airbag Control Module J234 obtains the passenger
information from J706 through a LIN interface.
The Airbag Control Module uses this information to
activate or deactivate the passenger airbag and the
passenger knee airbags. It is also used to activate
or deactivate the Front Passenger Airbag -DisabledIndicator Lamp K145.

J706
605_078

31

Passenger Occupant Detection System
System Overview
The Passenger Occupant Detection System Control
Module J706 is located under the passenger seat. Note
that there are different seat types and also different seat
occupant recognition control modules.
The software in the control modules is adapted specially
to the seat.

Front Passenger Airbag -DisabledIndicator Lamp K145

Passenger Occupant Detection
System Pressure Sensor G452

Airbag Control Module
J234

!
32

Connector Below the Seat

Passenger Occupant
Detection System
Control Module J706

Front Passenger
Safety Belt
Switch E25

Seat Cushion

Note
When repairing the seat occupant recognition system, always refer to ElsaWeb, Guided Fault Finding and the Electronic
Parts Catalog (ETKA).

605_079

Passenger Occupant Detection Sysytem
Gel Mat System Overview
This information is combined with the safety belt
tension to determine if a child seat is present. The
Airbag Control Module uses this information to activate
or deactivate the passenger airbag and the passenger
knee airbags. It is also used to activate or deactivate the
Front Passenger Airbag -Disabled- Indicator Lamp K145.

The gel mat design is specific for the US market. It is
made up of a gel may under the seat cushion. If weight
is put on the seat, gel in the mat transfers pressure
through a tube to the pressure sensor. This pressure
sensor calculates how much weight is on the seat.

Front Passenger Airbag -DisabledIndicator Lamp K145

Front Passenger
Safety Belt
Switch E25

Gel Mat

Passenger
Occupant
Detection System
Safety Belt Force
Sensor G453

Passenger Occupant Detection
System Pressure Sensor G452

Airbag Control Module
J234
Connector Below the Seat

!

Passenger Occupant
Detection System
Control Module J706

Seat Cushion

Note
Refer to SSP 991403 The 2005 Audi A6 Vehicle Introduction for more information on the gel mat PODS system.

33

Audi pre sense
Introduction
There are many terms for today's ever-evolving driver
assistance systems:

• Active safety
• Passive safety
• Integral safety
• Driver assistance systems
• Preventive occupant protection

Audi pre sense cannot prevent accidents from occurring.
Its purpose is to alert the driver to hazardous situations
and to assist the driver as much as possible.
The Audi pre sense system was made possible by
networking many vehicle systems. The individual control
modules transmit a continuous flow of information
using the vehicle's data bus systems. As a result, the
information is evaluated and the best possible course of
action can be initiated.