Audi TT (2007 year). Manual - part 219

9

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J234 Airbag control unit
J285 Control unit with display in dash panel insert
J393 Convenience system central control unit
J533 Data bus diagnostic interface (Gateway)
J623 Engine control unit

K19

Seat belt warning system warning lamp

K75

Airbag warning lamp

K145 Front passenger side airbag deactivated 

warning lamp (PASSENGER AIRBAG OFF)

N95

Airbag igniter, driver side

N250 Driver side airbag igniter -2-
N131 Front passenger side airbag igniter 1
N132 Front passenger side airbag igniter 2
N153 Driver seat belt tensioner igniter -1-
N154 Front passenger seat belt tensioner igniter -1-
N199 Side airbag igniter, driver side
N200 Side airbag igniter, front passenger side
N253 Battery isolation igniter

T16

16-pin connector, diagnosis connection

10

Occupant protection

Airbag control unit J234

Airbag control unit J234 and integrated electronics have the task of detecting a collision.
In the Audi TT Coupé ‘07 the airbag control unit is attached to the vehicle body in the area of the handbrake 
lever.
The airbag control unit is integrated in the CAN powertrain data bus so that it can exchange information with 
other control units.

The airbag electronics basically have the following 
main tasks:

–

Collision detection (front, side, rear)

–

Defined deployment of the belt tensioners, 
airbags and battery disconnect

–

Defined deployment of the second front airbag 
stage

–

Evaluation of all input information

–

Permanent monitoring of the complete airbag 
system

–

Independent energy supply via capacitor for 
a defined period of time 
(approx. 150 ms)

–

Fault display via failure warning lamp

–

Storage of error / and crash information

–

Indication of a collision event to other system 
components via the powertrain CAN bus or 
discrete collision output (conventionally wired)

–

Activate  seat  belt  reminder

To find out which components need replacing after an accident, refer to the valid Workshop Manual in 
ElsaWin.
An airbag control unit can only be replaced with a VAS tester running the "Guided Fault Finding" or "Guided 
Functions" application.

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Reference

For more information about the 
airbag control unit J234, refer to Self-
Study Programmes 323 Audi A6 `05 
and 361 Audi Q7.

11

Belt-on warning

The Audi TT Coupé ‘07 has a belt-on warning function for the driver.
The airbag control unit evaluates the information from the driver side belt switch E24 after ignition "on". If the 
driver is not wearing a seat belt, a visual warning is given by the seat belt warning system warning lamp K19 
integrated in the dash panel insert.If the system determines that the vehicle is moving, an audio warning is 
given in addition to the visual warning.As long as the ignition is on, the airbag control unit monitors the 
switched condition of seat belt switch E24. If seat belt status changes while terminal 15 is "on", the seat belt 
reminder will be reactivated.

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Time diagram for seat belt reminder

Visual and audio signals 
- Delayed seat belt fastening

Terminal 15

Road speed

Seat belt fastened

Seat belt warning system warning lamp

Audio signal

ON

OFF
V > 25 kph

v < 25 kph
yes

OFF
ON

OFF

No
ON

Time

Driver side belt switch E24

The "belt-on warning" function needs information 
on whether the driver's seat belt is fastened or not.

Seat belt switch E24 in the belt buckle is 
a mechanically actuated open-close switch.
The airbag control unit uses a resistance 
measurement to establish whether the seat belt is 
fastened or not.

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12

Occupant protection

Airbag

The Audi TT Coupé ‘07 has two-stage front airbags on the driver and front passenger sides. 
The airbag control unit selects the time interval between the two ignition stages (approx. 5 ms to 30 ms) 
according to severity and type of crash.
The loads acting on the driver or front passenger during an accident can be reduced through time-staggered 
ignition of the propellant charges.

Both propellant charges are always ignited. This ensures that no propellant charge remains active after the 
airbag is deployed.

Driver airbag

Airbag igniter I, driver side N95
Airbag igniter II, driver side N250

A gas generator with two pyrotechnic propellant charges is integrated in the driver's airbag.

Igniter I is activated electrically by the airbag control unit J234. The igniter flame passes through the container 
and ignites the ignition charge in the container. If the pressure produced by the ignition of the ignition charge 
is high enough, the flame will break through the container and reach the propellant charge through the 
perforated tube. Propellant charge I ignites and combusts. The developing gas destroys the foil seal, and 
filtered gas flows through the air outlet into the airbag. After a defined interval has expired, the airbag control 
unit activates igniter II, which in turn ignites propellant charge II directly. The gas produced by combustion of 
the propellant material flows through the raised end cap into the combustion chamber of propellant charge I. 
From here the gas flows through the filter into the airbag.

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Casing

Air outlet

Filter

Igniter I

Perforated tube

End cap

Ignition charge container

Propellant charge II

Igniter II

Filter

Foil seal

Air outlet

Foil seal

Propellant charge I