Tire Pressure Module: Description and Operation

GF40.15-P-5124GZ Tire Pressure Monitor Control Unit, Component Description
- Model 164
- with CODE (475) Tire pressure monitor (Siemens)
- except CODE (498) Japan version
- MODEL 164.8
- with CODE (470) Tire pressure monitor (base)
- with CODE (494) USA version






Location
The TPM [RDK] control unit is located on the load compartment fuse and relay box (F4).

Task
The TPM [RDK] control unit receives the current tire inflation pressure, tire temperature and other supplemental information from the four wheel sensors via the central TPM [RDK] antenna (A2/97), the left rear TPM [RDK] wheel antenna (A2/46) and the right rear TPM [RDK] wheel antenna (A2/47).

The TPM [RDK] control unit calculates valid limit values for the current tire temperature based on this information.

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).

Input signals (conventional wiring):
- Central TPM [RDK] antenna
- Left rear TPM [RDK] wheel antenna
- Right rear TPM [RDK] wheel antenna
- 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
- Country code
- Engine variant, 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.

There is a difference between low-line and mid-line versions. Both variants use the same control unit (hardware and software are identical).

The TPM [RDK] control unit uses a parameter to decide which functions are performed.