Detect seeping pressure loss, function

Function

Every tire loses air by diffusion over the course of time. To increase comfort, the driver receives a timely message that his tire pressures need correcting from the TPM system. The warning is issued directly after the end of the trip.

Temperature compensation

A temperature increase always leads to an increase in pressure in the wheel. The pressure measurements are temperature compensated in the TPM [RDK] control unit (N88) so that pressure changes can be detected. The values are converted into compensated pressure. Rapid temperature changes do not result in incorrect warnings.

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Soft warning

A warning is issued for a temperature compensated pressure loss of 0.25 bar relative to the stored filling pressure. The warning threshold is has an upper limit of 0.2 bar below the filling pressure.

Cancellation of warning:

 Warning threshold is no longer dropped below

 Filling detection was successful

 Manual reactivation of the system was carried out

Checking the warning condition while driving

If the warning threshold is dropped below for a period of
12 minutes a warning signal is stored in the memory of the TPM [RDK] control unit and is displayed in the instrument cluster (A1) upon ignition "OFF".

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Hard warning

The hard warning informs the driver of a distinct, safety-relevant pressure loss while driving. The warning complies with the requirements of legislation in the USA.

Parameters for a hard warning:

 A warning is issued for a pressure loss of 20 % or 0.5 bar relative to the stored filling pressure.

 The lower limit of the warning threshold is the minimum pressure
(1.5 bar).

 Temperature compensation for hot tires is limited at a temperature of 40° C over the ambient temperature. The warning threshold remains constant.

 The warning threshold is has an upper limit of 0.2 bar below the filling pressure.

 The warning is suppressed during filling detection.

The tire pressure monitor warning lamp (A1e66) in the instrument cluster is activated at the same time as the "hard warning". It does not go out until the TPM system is reactivated.

Cancellation of warning

When the engine is switched back on after a hard warning the tire pressure monitor warning lamp is initially reactivated. The warning is canceled when filling detection or a manual reactivation is successfully carried out.