Audi A3 Sportback, Service, Page: 41 / 60

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Operating principle
When a tyre loses air, its rolling circumference decreases. This increases the number of revolutions necessary
to cover a specific distance. This information is acquired by the wheel speed sender and evaluated by the ESP
control unit. In this way, the control unit recognises changes in tyre pressure. The ability of the control unit to
precisely evaluate measurement data is limited in certain dynamic operating conditions, such as cornering at
high speed, driving on rough roads, driving away and braking. In these situations, the information acquired is
not evaluated with regard to loss of pressure.
Calibration
System calibration is started by pressing the tyre pressure monitor button (for at least 2 seconds). During the
subsequent trip, the signals generated by the wheel speed sender are evaluated, with allowance being made
for the different vehicle operating states and speeds. The vehicle need only be driven for a few minutes in
order to obtain an initial "rough calibration". On completion of the calibration phase, the control unit will have
"learned" the nominal data for wheel speed as a function of the respective road speed and vehicle states. The
calibration must be performed after each tyre change, and after any change or adjustment in tyre pressure.
The driver is alerted to the loss of pressure by the warning lamp in the speedometer and by a single buzz tone
which sounds when the ignition is turned on. The warning is reset when a system recalibration is started.
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