Tire Pressure Module: Description and Operation

GF4015-P-5124RT Tire Pressure Monitor Control Unit, 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






Location
The TPM [RDK] control unit (N88) is located in the luggage compartment at the right on the wheelhouse.

Task
When comparing the actual tire pressure (determined by each respective sensor) with the stored set pressure and taking the tire temperature into account, the TPM [RDK] control unit calculates the limits for the current tire temperature.
If these limit values are dropped below, the TPM [RDK] control unit passes on an appropriate CAN signal to the instrument cluster (A1) depending on the pressure deviation. This CAN signal is processed in the instrument cluster and the appropriate information is displayed for the driver on the multifunction display (A1p13).
The TPM [RDK] control unit always transmits in the unit bar irrespective of whether this unit has been set by the driver in the instrument cluster or not. The instrument cluster then calculates and converts into the desired unit.

Input signals (conventional wiring):
- Central TPM [RDK] antenna (A2/97)
- Left rear TPM [RDK] wheel antenna (A2/46)
- Right rear TPM [RDK] wheel antenna (A2/47)
- Terminal 30 power supply

Via the CAN-engine compartment there is a connection to:
- Instrument cluster
- Front SAM control unit (N10)
- EIS [EZS] control unit (N73)
- Central gateway control unit (N93)

The following information is processed:

by the instrument cluster
- Initialization (function test, making of a controlled initial condition)
- Activation request
- Vehicle speed signal

from front SAM control unit
- Circuit 61 "ON" (for detecting "engine running")

from AAC [KLA] control and operating unit (N22)
- Outside air temperature

from EIS [EZS] control unit
- Battery voltage
- Terminal 15 "ON"

From the central gateway control unit
- Diagnosis
- Country code
- Engine, body variant
- Diagnosis active
- Wheel speeds
- Steering angle

The following information is issued via the CAN-engine compartment:

by the instrument cluster
- Tire pressures
- Messages relevant to function
- Messages relevant to operation

From the central gateway control unit
- Diagnosis

Design
The TPM [RDK] control unit consists of a high frequency receiver module, a control unit circuit board with microprocessor control and an interface for the CAN data bus.
One differentiates between low-line and mid-line versions. In both versions the same control unit is used (hardware and software are identical).
The TPM [RDK] control unit draws on a parameter to decide which functions should be executed.