GF40.15-P-0001LEA Tire Pressure Monitor Function
GF40.15-P-0001LEA Tire pressure monitor function
- with CODE (475) Tire pressure monitor (Premium)
Function requirements
^ "Circuit 15 ON" status
^ Tire pressure monitor (TPM [RDK]) system functional
The status of circuit 15 is provided by the EIS [EZS] control unit (N73) via the chassis CAN (CAN E).
General
The TPM system assists the driver when checking the tire inflation pressure as of a vehicle speed v greater than 10 to 20 km/h (no stationary monitoring) and thus serves active safety.
The tire pressure monitoring system monitors the air pressure and temperature in the individual tires. A specified pressure stored previously (specified value) for each tire is used as a comparison value.
If a relevant loss of pressure occurs, a warning message is issued to the driver, when possible with the affected location. The tire pressure measuring range extends from p = 0 to 6.375 bar.
The TPM [RDK] comprises the following component functions:
^ Tire pressure sensing function sequence
^ Warning message function sequence
^ Manual restart function sequence
^ Automatic fill detection function sequence, except code (494) USA version
^ Learn mode function sequence
Tire pressure sensing function sequence
While driving, the TPM system continuously monitors the tire pressure of all wheels as of a vehicle speed v greater than 10 to 20 km/h (no stationary monitoring).
The left front TPM wheel sensor (A69/1), right front TPM wheel sensor (A69/2), left rear TPM wheel sensor (A69/3) and right rear TPM wheel sensor (A69/4) transmit a data telegram every t = 60 s while driving or when detecting a pressure change (p greater than 0.1 bar) since the last regular data telegram. 6 frames (more reliable signal reception) with tire inflation pressure, tire air temperature, the wheel identification number and status information (e.g. manufacturer, direction of rotation, operating mode, battery condition) are transmitted in this data telegram. The data are conveyed via radio frequency to the TPM [RDK] control unit (N88). Axle localization is done by evaluating the receiver input level (field strength of transmitted high frequency signals (433 MHz)) from the wheel sensors. The side localization is based on right-left information (phase offset of the acceleration sensors integrated in the wheel sensors) of the wheel sensors.
The warning logic of the TPM control unit also takes account of the outside temperature (for temperature compensation of air pressures in each tire (isochore)) and the vehicle speed.
The outside temperature is recorded by the outside temperature indicator temperature sensor (B14) and transmitted to the front SAM control unit with fuse and relay module (N10/1) via direct lines. From there the message is passed on to the TPM control unit via the following path:
- Interior CAN (CAN B)
- Central gateway control unit (N93)
- Chassis CAN
The vehicle speed is transmitted as a message by the instrument cluster (A1) to the TPM [RDK] control unit via the following path:
- Central CAN (CAN F)
- Central gateway control unit
- Chassis CAN
Any warning messages and menu displays are shown on the multifunction display (A1p13) in the instrument cluster. Depending on the warning message the tire pressure monitor warning lamp (A1e66) is also actuated permanently in the instrument cluster. On vehicles with code (494) USA version, the tire pressure monitor warning lamp in the instrument cluster will flash for t = 60 s if there is a malfunction in the tire pressure monitoring system. Then it will be actuated permanently. Following the next ignition sequence, this procedure will repeat itself until the fault is eliminated.
On vehicles with code (494) USA version, there is no temperature compensation of air pressures for each tire (isochore) at low temperatures.
Warning message function sequence
A warning message, where possible including the affected location, is issued when a relevant loss of pressure has been detected in at least one of the tires. The driver is given feedback from the multifunction display or the tire pressure monitor warning lamp in the instrument cluster.
The feedback via the multifunction display or actuation of the tire pressure monitor warning lamp in the instrument cluster takes place by the TPM [RDK] control unit via the following path:
- Chassis CAN
- Central gateway control unit
- Central CAN
The warning messages are made up of the following subfunctions:
^ Soft warning message function sequence
^ Hard warning message function sequence
^ Leak detection function sequence (rapid pressure loss)
Soft warning message function sequence
Tires lose air over the course of time through diffusion.
This is why convenient feature provides the driver with a message in good time about the need to correct tire pressures.
The soft warning message occurs for t = 30 s only after end of travel (status "circuit 15 OFF").
The warning threshold is defined as follows:
- Pressure loss of p greater than 0.25 bar
If while driving the pressure loss of a wheel is uninterrupted above a warning threshold for a period of t = 12 min, an acoustic warning is set. This warning signal is stored in the memory of the TPM control unit and displayed after end of travel (status "circuit 15 OFF") in the instrument cluster's multifunction display.
If the tire pressure increases again to more than p = 0.1 bar under the stored specified value, the warning message is suppressed.
The warning message is retracted if one of the following actions takes place:
- Warning threshold no longer exceeded
- Successful automatic fill detection, except code (494) USA version
- Manual restart
Hard warning message function sequence
A pressure loss of greater than 20% can over time cause irreversible damage to the tire. A hard warning message is therefore shown during travel in the multifunction display and the tire pressure monitor warning lamp is permanently lit to draw the driver's attention to this significant and safety-relevant loss in pressure. The warning threshold is defined as follows:
- Pressure loss of 20 % or p ≥ 0.5 bar
In the event of a pressure loss above the warning threshold after t = 5 min at the latest a red warning message "Check tires" and the position detail of the tire in question is shown in the multifunction display as well as the tire pressure monitor warning lamp actuated permanently in the instrument cluster.
In the event of a leak being detected (air removal process p greater than 0.2 bar/min) the driver is warned with the red warning message "Important: tire defective" and the position detail of the tire in question in the multifunction display as well as by permanent actuation of the tire pressure monitor warning lamp in the instrument cluster.
If no assignment of wheel positions could be performed by the TPM [RDK] control unit, no position detail takes place for red warning messages, but only the red symbol "Tire with and the red additional text "Check tire pressures" or "Tire pressure, tire defective" takes place in the multifunction display in the instrument cluster as well as permanent actuation of the tire pressure monitor warning lamp.
The actuation of the tire pressure monitor warning lamp with the respective red warning message in the multifunction display in the instrument cluster is repeated during the next ignition sequence, if no cancellation occurs due to one of the following actions
- Warning threshold no longer exceeded
- Successful automatic fill detection, except code (494) USA version
- Manual restart
Leak detection function sequence (rapid pressure loss)
If while driving a progressive pressure loss is determined in a certain time segment (gradient), a tire defect must be assumed. In this case a warning message is triggered, even before the triggering criterion for the hard warning message is reached. The warning message normally appears no later than t = 120 s following the commencement of a pressure loss of p greater than 0.1 bar/min. The driver is warned by the red warning message "Important: tire defective" and the position detail of the tire in question in the multifunction display as well as by permanent actuation of the tire pressure monitor warning lamp in the instrument cluster.
If no assignment of the wheel positions could still be performed by the TPM [RDK] control unit, no position detail takes place for red warning messages, but only the red symbol "Tire with !" and red additional text "Tire pressure: tire defect" in the multifunction display in the instrument cluster as well as permanent actuation of the tire pressure monitor warning lamp.
The actuation of the tire pressure monitor warning lamp with the respective red warning message in the multifunction display in the instrument cluster is repeated during the next ignition sequence, if no cancellation occurs due to one of the following actions
- Warning threshold no longer exceeded
- Successful automatic fill detection, except code (494) USA version
- Manual restart
Manual restart function sequence
When the TPM [RDK] system is restarted, the tire pressures set by the driver are adopted by the TPM [RDK] control unit as the new specified values. Using the system selection button (S110s3) and scroll forward and back button (S110s1) in the left multifunction steering wheel button group (S110) it is possible to scroll in the service menu and tire pressure submenu in the multifunction display in the instrument cluster. The message "Tire pressure display appears after driving for a few minutes" will be shown in the instrument cluster's multifunction display. Pressing the scroll forward and back button in the lower subfield changes the display in the multifunction display in the instrument cluster to "Accept current pressures as new guideline value. Accept with OK". Pressing the OK button (S110s6) confirms the acceptance with the display "Tire pressure check restarted" in the multifunction display in the instrument cluster. Then the system will switch to the "Tire pressure" display showing the current tire pressures matched to their locations.
The signals from the left multifunction steering wheel button group are read in by the steering column tube module (N80) via the steering LIN (LIN E1) and transmitted to the instrument cluster via the following path:
- Chassis CAN
- Central gateway control unit
- Central CAN
The TPM [RDK] control unit receives the message for restarting the TPM system from the instrument cluster via the following path:
- Central CAN
- Central gateway control unit
- Chassis CAN
The TPM control unit then internally deletes all specified pressures (specified values) for each tire and all warning messages for the multifunction display as well as any actuation commands for the tire pressure monitor warning lamp in the instrument cluster.
Then the TPM control unit takes the current tire pressures and uses them as the specified pressures (specified values) individually for each tire.
After the start of a trip, as of a vehicle speed v greater than 10 to 20 km/h the new specified pressures (specified values) for each tire are checked for compliance with the minimum pressure and for plausibility. If everything is OK, the specified values and the warning thresholds are automatically adjusted. Otherwise a warning message will appear in the instrument cluster's multifunction display or the tire pressure monitor warning lamp will be permanently actuated.
On vehicles with code (494) USA version, the tire pressure monitor warning lamp in the instrument cluster will flash for t = 60 s if there is a malfunction in the tire pressure monitoring system. Then it will be actuated permanently. Following the next ignition sequence, this procedure will repeat itself until the fault is eliminated.
Automatic fill detection function sequence, except code (494) USA version
Automatic fill detection takes place, if a pressure change of p greater than 0.2 bar has been detected at least 2 wheels at a vehicle speed v greater than 10 to 20 km/h. Temperature-compensated and filtered pressure values are used for comparison and checked for compliance with the minimum pressure (specified pressures (specified values) for each tire) as well as for plausibility. If everything is OK, the specified values and the warning thresholds are automatically adjusted. Otherwise a warning message appears in the multifunction display in the instrument cluster and the tire pressure monitor warning lamp is actuated permanently.
Learn mode function sequence
With new wheels or a longer parking time of t greater than 5 min, the separate wheel detection and axle assignment must be completed first via the wheel sensors.
After driving for approx. t = 10 min a new wheel sensor is taught in with a new wheel identification number and monitored.
Axle localization is done by evaluating the receiver input level (field strength of transmitted high frequency signals (433 MHz)) from the wheel sensors. The side localization is based on right-left information (phase offset of the acceleration sensors integrated in the wheel sensors) of the wheel sensors.
The "learning process function sequence" consists of the following subfunctions:
^ Initial start-up
^ Fault monitoring
Initial start-up
The "Initial start-up" is further broken down according to the two options available for teaching in the wheel sensors:
^ Learning process in workshops or correction by entering identification number with the Diagnosis Assistance System (DAS)
^ Learning process in workshops or correction with the E-Tester or CANDI
Learning process in workshops or correction by entering identification number with the Diagnosis Assistance System (DAS)
When working with DAS, follow the "Initial start-up" routine. There are 2 variants: "Initial start-up with unknown wheel IDs" and "Initial start-up with known wheel IDs".
Learning process in workshops or correction with the E-Tester or CANDI
New wheel sensors can be taught in with the routine "Check for WU Remeasure Transponder". With this routine, it is possible to choose between teach-in with Trigger tool MB2000E or teach-in via pressure change. This routine is started via diagnosis and is identical for all wheel positions.
For teach-in with Trigger tool MB2000E, the respective wheel sensor must be triggered. As a result of this the wheel sensor transmits a data telegram from which the wheel identification number is read out.
For teach-in via pressure change, the pressure at the corresponding wheel must be changed by p = 0.3 bar. The wheel sensor then transmits data telegrams with the changed pressure value (delta_p Frames) to the TPM [RDK] control unit. The wheel identification number is read out from these data telegrams.
The result is queried with the service "Check for WU Remeasure Transponder: Request results WU ID". The wheel identification numbers determined must then be written to the respective position by the operator in the diagnosis service Download "transmitter ID's" (Left Front, Right Front, Right Rear and Left Rear). OK must also be written to the service download "Axle/Side Location Status".
The TPM [RDK] control unit checks the plausibility of the wheel identification numbers and permits only one identification number per wheel.
Fault monitoring
"Fault monitoring" is further broken down according to the 3 possible causes of faults for the wheel sensors:
^ No wheel sensors present
^ Individual wheel sensors defective or not present
^ Radio interference
No wheel sensors present
After a parking time t greater than 5 min the TPM [RDK] control unit checks at the start of a trip whether all high frequency signals (433 MHz) are received from the wheel sensors. If wheels without wheel sensors are installed, the following fault message appears after t = 10 min in the instrument cluster's multifunction display: "Tire pressure monitor inoperative, No wheel sensors". This fault message will no longer appear following the next ignition sequence.
In the tire pressure submenu of the service menu instead of the display "Tire pressure" with the current tire pressures and their position detail of the individual tires is the note "Tire pressure monitor inoperative, no wheel sensors".
On vehicles with code (494) USA version, the fault message "Tire pressure monitor inoperative, No wheel sensors" will reappear in the instrument cluster's multifunction display following the next ignition sequence.
Individual wheel sensors defective or not present
After a parking time of t greater than 5 min the TPM [RDK] control unit checks at the start of a trip whether all high frequency signals (433 MHz) are received from the wheel sensors. If fewer than 4 wheel sensors are fitted, after driving for t = 10 min the fault message "No wheel sensor system" with the measured, received, current tire pressures and their position detail of the individual tires appears in the multifunction display in the instrument cluster. The current tire pressure(s) not measured is or are displayed with lines.
Radio interference
If all 4 wheel sensor signals are received properly during travel and then there is suddenly no reception of the high-frequency signal (433 MHz) for t = 10 min, the tire pressure monitoring system will assume that there is temporary radio interference. The fault message "Tire pressure monitor currently unavailable" will appear in the instrument cluster's multifunction display. This warning message will disappear automatically as soon as reception of the high frequency signal (433 MHz) is regained.
