Tire Pressure Monitor, Function - GF40.15-P-0001RF
Model 205, Model 253 with code 475 (Tire pressure monitoring system)
Block diagram
Function requirements, general
- Status "Circuit 15 ON"
- Tire pressure monitor (TPM [RDK]) system functional
The circuit 15 status is sent by the electronic ignition lock control unit over the user interface CAN.
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.
If a relevant loss of pressure occurs, a warning message is issued to the driver, when possible with the affected location. The measuring range of the tire pressure is between p = 0 to 637.5 kPa.
The TPM [RDK] comprises the following subfunctions:
- Function sequence for tire pressure sensing
- Function sequence for warning message
- Function sequence for manual restart
- Function sequence for automatic fill detection
- Function sequence for automatic teach-in process for tire pressure monitor control unit
- Function sequence for run-on
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 out data telegrams during a journey every t = 60 s to the tire pressure monitor control unit. These data telegrams contain the pressure, the tire air temperature, the individual serial number and the status information (rolling direction, operating mode etc.). The data are transmitted by radio to the tire pressure monitor control unit.
If, during a journey, the tire pressure on at least one wheel is permanently below the warning threshold, a warning tone is set and stored in the memory of the tire pressure monitor control unit. A warning is displayed on the instrument cluster and the tire pressure monitor warning lamp is actuated.
The warning messages are canceled if one of the following events occurs:
- Filling to specified pressure
- Successful automatic fill detection
- Manual restart
Function sequence for hard warning
During vehicle travel, the hard warning informs the driver of any significant, safety-relevant pressure loss.
Warning threshold:
- Pressure loss > 20 %
If the tire pressure drops below the value specified by the warning threshold, then at the latest after t = 5 min a warning message is shown on the instrument cluster, 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 = 20 kPa/min and is shown as a warning message "Warning! Tire defect" on the instrument cluster.
Axle localization is performed by evaluating the reception level of the tire pressure sensors. The sides are localized by evaluating the direction of rotation information.
Additional input factors
In addition, the tire pressure monitoring control unit incorporates the outside temperature and the vehicle speed into the warning logic. The outside temperature is measured by the outside temperature sensor and directly read in by the front SAM control unit. The front SAM control unit sends the signal over the interior CAN, electronic ignition lock control unit and the user interface CAN to the instrument cluster. The instrument cluster sends the outside temperature and the vehicle speed over the user interface CAN to the tire pressure monitor control unit.
Function sequence for warning message
The control unit tire pressure monitoring system continuously evaluates the data telegrams of the tire pressure sensors.
If a relevant pressure loss is detected at a tire, the tire pressure monitor control unit forwards a request to display a warning message over the user interface CAN to the instrument cluster.
The instrument cluster displays a warning message and actuates the tire pressure monitor warning lamp.
The warning messages are made up of the following subfunctions:
- Function sequence for soft warning
- Function sequence for hard warning
- Function sequence for leak detection (rapid pressure loss)
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:
- Pressure loss > 12 % for t = 8 min (except CODE 494 (USA version))
- Pressure loss > 12 % for t = 18 min (with CODE 494 (USA version))
A warning message is canceled for one of the following events:
- Filling to specified pressure
- Successful automatic fill detection
- Manual restart
When switching the ignition on again after a leak warning message, the tire pressure monitor warning lamp in the instrument cluster is initially actuated. 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 tire pressure monitoring control unit as the new specified values.
The left multifunction steering wheel button group and the right multifunction steering wheel button group can be used in the instrument cluster to call up the "Service/tire pressure" menu, to browse through it and to restart the system.
The signals are read in by the steering column tube module control unit over the steering LIN and sent over the chassis FlexRay, electronic ignition lock control unit and the user interface CAN 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 tire pressure monitor control unit filters the new pressure values for t = 5 min. from the start of the journey and checks their 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 = 20 kPa has been detected in at 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 for tire pressure monitor 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.
In the case of axle assignment the rear wheels which are closer to the receiver receive stronger signals than the front wheels which are further away. The reception levels for the tire pressure sensors on the rear axle are greater than on the front axle.
If the tire pressure monitor control unit is replaced, then Xentry Diagnostics must be used to perform the guided "Initial startup" routine.
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.
As a result of the manually-performed reduction in tire pressure, the deflation causes each tire pressure sensor to send a data log from which the corresponding wheel ID can be read out.
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 power-down
- Circuit 15 OFF
Function sequence for run-on
After switching off the ignition the tire pressure monitor control unit remains active for another t = 19 minutes, and it can receive signals from the tire pressure sensors by radio frequency. The user interface CAN switches in power-down into the sleep mode.
| Electrical function diagram for tire pressure monitor (TPM [RDK]) | PE40.15-P-2050-97FBA | ||
| Tire pressure monitor (TPM (RDK)) messages | GF40.15-P-0001-08RF | ||
| Overview of system components for tire pressure monitor (RDK) | GF40.15-P-9999RF |