Tire Pressure Sensor: Description and Operation

GF40.15-P-5126RT Wheel Sensor, Component Description
MODEL 251.1 /0 with CODE (475) Tire pressure monitor (Siemens)
MODEL 251.1
with CODE (470) Tire pressure monitor (base)
with CODE (494) USA version








Design
Together with the filling valve, the TPM [RDK] wheel sensors form a compact unit and are fitted into the rims like a screw-on valve. Modifications to the rims are not required.

The following are located in the housings:
- pressure sensor
- temperature sensor
- transmission stage
- Lithium battery for internal voltage supply

Function
As part of energy management the TPM wheel sensors automatically switch between the following operating modes:
- Energy-saving mode, as long as the component is in store, not fitted to the vehicle.
- As long as no pressure change which is dependent on specified value, at intervals of 55 seconds data telegrams are transmitted for system monitoring and for detecting very slow pressure changes.
- The measurement rate and transmission rate is increased (0.8 seconds) if a rapid pressure change has been detected at a wheel. The TPM control unit (N88) is thus provided with a number of measured values within a short period of time, allowing reliable evaluation of the pressure change.
- Shutdown of the measurement and transmission electronics at temperatures > 120 C or 248 F, because reliable recording of data and data transfer cannot be assured under these driving conditions. The measurement and transmission electronics are reactivated automatically on cooling to <100 C or 212 F.

Energy management
Due to the finite space the battery size and as a result the battery capacity is limited An intelligent energy management system provides an estimated service life of approx. 10 years with a single battery.

Note: The respective TPM wheel sensor must be replaced in the event of a defect in the battery.