Audi TT (2007 year). Manual — part 239

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.

37

Design and function

Data processing in the Audi TT is performed by con-
trol unit J793, and is no longer an integral part of
the ESP control unit. The control unit is located
behind the dash panel insert.

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Tyre pressure monitor display

control unit 2 J793

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.

38

Wheels and tyres

Design and function

Using a new evaluation method, it is now possible
to detect simultaneous pressure loss to at multiple
wheels. Tyre pressures are monitored simultane-
ously using two different concepts.

1. Tyre circumference monitoring

– Tyre circumference decreases as a function of

loss of pressure. As a result the wheel must
rotate more quickly to cover the same distance as
a fully inflated tyre. Wheel speeds are transmit-
ted to control unit J793 by the ESP control unit. In
the current Audi A3, the wheel speeds of the
diagonal wheels are added and both diagonal
sums are correlated with one another. In this
way, allowance is made for different wheel
speeds when cornering. In the Audi TT, the tyre
circumferences are compared axle by axle and
side by side.
Allowance is made for yaw rate and steering
angle when cornering.

2. Tyre vibration monitoring

– Torsional vibration is excited in each tyre while

rolling, due to road surface unevenness. These
vibrations can be determined by evaluating the
wheel speed signals. When the tyre pressure
decreases, the vibration characteristics
change.This monitoring concept, which is an
additional feature compared to the Audi A3, it is
now possible to reliably detect simultaneous loss
of pressure at multiple wheels, as for example
occurs over time at all four wheels due to diffu-
sion.

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.

39

Operation and displays

Tyre pressure monitoring is activated with the SET
key. This function must always be activated when
tire pressures are changed or different wheels/tyres
are fitted to the vehicle. This can only be done when
the ignition is on and the vehicle stationary. The
SET key must be pressed for at least 5 seconds in
order to activate the tyre pressure monitoring
function.

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Warnings are always indicated by the warning lamp
in the dash panel insert.

For this purpose, the warning lamp is activated in
two colours.

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The following displays are possible:

– In the event of a rapid loss of pressure at a single

wheel (tyre damage), the red warning lamp is
activated. If the vehicle a driver information sys-
tem, an additional text display appears indicat-
ing the position of the wheel affected.

– In case of slow loss of pressure, which occurs

gradually at multiple wheels due to diffusion, the
red warning lamp is also activated. In this case,
the optional text display appears but no posi-
tional information is given. The displays are acti-
vated when the tyre pressure drops below an a
coded minimum value.

– When system faults are detected, the yellow

warning lamp is activated.

Protected by copyright. Copying for private or commercial purposes, in part or in whole, is not
permitted unless authorised by AUDI AG. AUDI AG does not guarantee or accept any liability
with respect to the correctness of information in this document. Copyright by AUDI AG.

40

Wheels and tyres

Operation and displays

The teach-in process is performed once after the
SET key is pressed for the low tyre pressure indica-
tor. During the next trip, the control unit saves the
measured wheel speeds and the vibration charac-
teristics of the wheels in various vehicle operating
states. The vehicle operating states are basically
defined by the following parameters: vehicle speed,
steering angle, transverse acceleration and yaw
velocity. These teach-in values subsequently make
up the target data which is used for monitoring.
After approximately 10 minutes of driving, it is
already possible to detect a breakdown (rapid loss
of pressure) . Approximately 60 minutes of driving
are required to detect diffusion loss (slow loss of
pressure).

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Vehicle self-diagnostics

Select diagnostic
function

4C - Tyre pressure monitor II
8J0907274

8J0907274

J793 TPM+

H03

--- 0100

Coding 614100
Dealership number 98765

Display all diagnostic functions
02 - Query fault memory
05 - Clear fault memory
06 - End of output
07 - Encode control unit
Encoding the subbus system
08 - Read data block
16 - Access authorisation
Read out Challenge immobiliser IV
Activate immobiliser IV
Identification services

Goto

Print

Service work

Address

The system can be addressed in the
diagnostic tester under the address:
4C Tyre pressure monitor II.