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Tire Pressure Monitor, Function - GF40.15-P-0001KJ

MODEL 453.0/3/4 

with CODE V41 (Tire pressure monitoring system) 

Block diagram 

G12094968Courtesy of MERCEDES-BENZ USA

Function requirements, general 

TPM [RDK], general information 

The tire pressure monitor assists the driver by monitoring the tire pressure, thereby contributing to active safety.

The tire pressure monitor (TPM) system monitors the air pressure in the individual tires. A previously stored specified pressure is used as a comparison value for the front wheels and rear wheels.

In the event of a relevant pressure loss a warning message is issued to the driver. The tire pressure measuring range extends from 0 to 6.375 bar.

The TPM [RDK] comprises the following subfunctions:

Function sequence for tire pressure sensing 

The tire pressure monitor (RDK) continuously monitors the tire pressure for all rotating wheels, while driving.

The 4 tire pressure sensors send data telegrams to the center SAM control unit every 60 seconds during a journey. These data telegrams contain the pressure, tire air temperature, wheel identifier (wheel ID) and status information (direction of rotation, operating mode, etc.). The data are conveyed via two-way radio to the center SAM control unit.

Additional input factors 

The center SAM control unit also takes the vehicle speed into account in its warning logic.

IMPORTANT Required warning or notification messages are displayed on the multifunction display of the instrument cluster (only with code K36 (Instrument cluster with color 8.9 cm (3.5") display))

Function sequence for warning message 

The center SAM control unit continuously evaluates the data telegrams of the tire pressure sensors.

If a relevant pressure loss is detected at a tire, the center SAM forwards a request to display a warning message to the instrument cluster via the interior CAN.

The instrument cluster outputs a warning message via the multifunction display (only with code K36 (Instrument cluster with color 8.9 cm (3.5") display)) and actuates the tire pressure monitor warning lamp.

The warning messages are made up of the following subfunctions:

Function sequence for soft warning 

The soft warning is issued during the journey. Tires lose air over the course of time through diffusion. A comfort function therefore notifies the driver in good time about the need to correct tire pressures.

The warning threshold is defined as follows:

If, during a journey, the tire pressure on at least one wheel is permanently below the warning threshold, an acoustic warning is set and filed in the memory of the center SAM control unit. A warning is displayed on the multifunction display (only with code K36 (Instrument cluster with color 8.9 cm (3.5") display)) and the tire pressure monitor warning lamp is additionally actuated.

The warning message is canceled if one of the following events occurs:

Function sequence for hard warning 

During vehicle travel, the hard warning informs the driver of any significant, safety-relevant pressure loss.

The warning threshold is defined as follows:

If the tire pressure drops below the value specified by the warning threshold, after max. t = 5 min a warning message is displayed on the multifunction display (only with code K36 (Instrument cluster with color 8.9 cm (3.5") display)) and the tire pressure monitor warning lamp is actuated. During the subsequent driving cycle, the tire pressure monitor warning lamp remains actuated until the problem is rectified.

If the instantaneous tire pressure increases to the specified pressure or if a manual restart of the tire pressure monitor is performed, then the tire pressure monitor warning lamp is automatically extinguished and the warning message also goes out.

Function sequence for leak detection (rapid pressure loss) 

If while driving a progressive pressure loss is detected in a particular time section (gradient), a tire defect has to be assumed. In this case a warning is triggered even before the triggering criterion for the hard warning is reached.

The warning is generally issued at the latest t = 120 s after the start of a pressure loss of p = 0.2 bar/min and is shown as a warning message "Warning! Tire defect" on the multifunction display in the instrument cluster (only with code K36 (Instrument cluster with color 8.9 cm (3.5") display)).

A warning message is canceled for one of the following events:

When the engine is switched back on after a leak warning message, the tire pressure monitor warning lamp in the instrument cluster is initially activated. If, after starting a journey, the pressures match the specified value again, the tire pressure monitor warning lamp goes off.

Function sequence for manual restart 

When the TPM [RDK] system is restarted, the tire pressures set by the driver are adopted by the center SAM control unit as the new specified values.

IMPORTANT With code K36 (Instrument cluster with color 8.9 cm (3.5") display):

It is possible to access the menu "Settings/tire pressure monitor" on the instrument cluster, scroll in it and restart the system via the left multifunction steering wheel button group. The signals are looped directly through to the audio gateway control unit via the steering wheel clock spring contact and sent to the instrument cluster over the interior CAN.

IMPORTANT For more information on the menu displays, see document "Tire pressure monitor (TPM) messages".

IMPORTANT With code K35 (Instrument cluster with monochrome display):

It is possible to initiate a manual restart in the instrument cluster using the menu navigation button group. The corresponding symbols flash for t = 5 s and then light up. The system is then restarted. The signals are transmitted directly to the instrument cluster.

The pressure thresholds for the warnings are determined on the basis of the pressure values at the time of the restart. Operation feedback is issued immediately over the instrument cluster.

The center SAM control unit filters the new pressure values for t = 5 min as of the start of the journey and checks them for plausibility. The medium pressure value on each axle is then stored as the new specified value for pressure monitoring.

Function sequence for automatic fill detection 

Automatic fill detection takes place, if at the start of a journey a pressure change of more than p = 0.2 bar has been detected at a least 2 wheels. For comparison, temperature-compensated and filtered pressure values are drawn on and compared against the values for the last journey. After approx. t = 5 min. journey and a successful plausibility check, the new tire pressures are automatically adopted as specified values. A pressure differential between the right and left wheel of p > 17 % is regarded as implausible.

Function sequence for automatic teach-in process of center SAM control unit 

Following an extended parking period of t > 19 minutes, the automatic detection and localization of the tire pressure sensors is started when the journey starts.

A new tire pressure sensor is taught-in automatically after driving for 10 minutes. Side localization is conducted by evaluating the rolling direction, based on right-left information from the tire pressure sensors.

IMPORTANT If the center SAM control unit is replaced, then XENTRY Diagnostics must be used to perform the guided "Initial startup" routine.

IMPORTANT If it is necessary to teach in tire pressure sensors, the teach-in process must be performed using Xentry Diagnostics in the "Control unit adaptation" menu, "Write wheel electronics identification number" submenu.

IMPORTANT The guided manual tire pressure lowering process requests the tire pressure sensors to send a data protocol one after the other, from which the corresponding wheel identification number can be read out.

IMPORTANT If the Trigger tool is used, the individual tire pressure sensors have to be triggered one after the other to ensure that the corresponding data protocol is sent from which the required wheel ID can then be read out.

Function requirements for run-on 

Function sequence for run-on 

After switching off the ignition, the center SAM control unit remains active for another t = 19 minutes, and it can receive signals from the tire pressure sensors by radio frequency.

  Electrical function diagram for tire pressure monitor (TPM [RDK])   PE40.15-P-2050-97BBA 
  Tire pressure monitor (TPM (RDK)) messages Vehicles with code K36 (Instrument cluster with color 8.9 cm (3.5") display) GF40.15-P-0001-08KJ 
  Overview of system components for tire pressure monitor (RDK)   GF40.15-P-9999KJ 
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