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.