GF40.15-P-0001LE Tire Pressure Monitor Function
GF40.15-P-0001LE Tire pressure monitor function
- with CODE (494) USA version
- with CODE (475) Tire pressure monitor (premium)
Function requirements, general
^ Circuit 15 ON
^ Tire pressure monitor (TPM [RDK]) system functional
The status of circuit 15 ON is provided by the EIS [EZS] control unit (N73) via the interior CAN (CAN B).
General
The TPM [RDK] system assists the driver in checking the tire inflation pressure thus contributing to active safety. The TPM [RDK] system monitors the air pressure in the individual tires. A previously stored specified pressure is used as a comparative value. In the event of a relevant pressure loss a warning message is issued to the driver. The tire pressure measuring range extends from p = 0 to 5.5 bar.
A spare wheel which may be present is not monitored.
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
During a trip the TPM system continuously monitors the tire pressure of each wheel (with circuit 15 OFF run-on time for t = 20 min).
During a trip the left front TPM [RDK] wheel sensor (A69/1), right front TPM [RDK] wheel sensor (A69/2), left rear TPM [RDK] wheel sensor (A69/3) and right rear TPM [RDK] wheel sensor (A69/4) transmit data telegrams every t = 60 s. The pressure, tire air temperature, individual serial number and status information (manufacturer, direction of rotation, operating mode etc.) are contained in these data telegrams.
The data are received by the TPM central antenna (A2/97) and passed on via direct lines to the TPM [RDK] control unit (N88). In addition, the TPM [RDK] control unit incorporates the outside temperature and the vehicle speed in the warning logic. The data are sent over interior CAN.
The outside temperature is recorded by the outside temperature indicator temperature sensor (B14) and transmitted by the front SAM control unit with fuse and relay module (N10/1) via the interior CAN.
The wheel speeds are recorded by the ESP control unit (N47-5) by evaluating the signals from the left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) and right rear rpm sensor (L6/4) and transmitted to the central gateway control unit (N93) via the chassis CAN (CAN E). This transmits the signals further to the instrument cluster via the central CAN (CAN F) (A1). The instrument cluster determines the vehicle speed from the signals and transmits this further via the central CAN to the central gateway control unit which transmits the vehicle speed via the interior CAN.
Warning and information messages which may occur are shown in the multifunction display (A1p13) of the instrument cluster.
Warning message function sequence
A warning is issued when a relevant loss of pressure has been detected in at least one of the tires.
The warning is issued with position detail.
The driver receives feedback via the multifunction display in the instrument cluster or via the tire pressure monitor warning lamp (A1e66).
The warning messages are made up of the following subfunctions:
^ Soft warning function sequence
^ Hard warning function sequence
^ Leak detection function sequence (rapid pressure loss)
Soft warning function sequence
The warning is issued immediately after a trip is ended (circuit 15 OFF).
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.
Warning threshold:
- Pressure loss of p greater than 0.25 bar
If the tire pressure loss in at least one wheel exceeds the warning threshold while driving and uninterrupted over a period of t = 12 min, an acoustic warning is set, stored in the memory of the TPM [RDK] control unit and displayed in the instrument cluster after the end of the trip (circuit 15 OFF).
If the tire pressure increases again to at least p = 0.1 bar under the stored specified value, the warning message is suppressed.
Warning cancellation:
- Warning threshold no longer exceeded
- Successful automatic fill detection (except code (494) USA version)
- Manual restart
Hard warning function sequence
While driving the hard warning informs the driver of a significant pressure loss which is relevant to safety. Warning threshold:
- Pressure loss of 20 % or p ≥ 0.5 bar
If the pressure loss exceeds the warning threshold, a warning message is shown in the multifunction display after t = 5 min at the latest and the tire pressure monitor warning lamp is actuated.
In the event of a very large pressure loss (pressure is p ≥ 0.2 bar below the pressure value of the warning threshold) the warning message takes place after t = 1 min at the latest.
If a leak is detected (air release p greater than 0.2 bar/min) the message "Warning! Tire defective" is displayed to the driver. The tire pressure monitor warning lamp is actuated together with a hard warning, which is repeated during the next ignition sequence. Warning cancellation:
Successful automatic fill detection
- Manual restart
Leak detection function sequence (rapid pressure loss)
If progressive pressure loss is detected during a certain period (gradient) of time while driving, it is assumed that a tire is defective. In this case a warning is triggered, even before the triggering criterion for the hard warning is reached. As a rule the warning takes place t = 60 s at the latest after the start of a pressure loss of 0.2 bar/min and is shown in the multifunction display of the instrument cluster as a warning message (red) "Important: tire defect".
Warning cancellation:
During an ignition sequence the warning can be canceled by successful filling detection or by manual reactivation. 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 new pressure values exist after the start of a trip and no warning criterion is met, the tire pressure monitor warning lamp goes out and the warning note is canceled. The warning is likewise canceled by successful fill detection (except code (494) USA version) or by 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.
It is possible scroll in the "TPM" menu in the instrument cluster using the left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111). You can reach the submenu for restarting the TPM system with the OK button (S110s6).
The signals are read in by the steering column tube module (N80) and transmitted to the central gateway control unit via the chassis CAN. From there the signals are transmitted to the instrument cluster via the central CAN. 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 TPM [RDK] control unit filters the new pressure values for t = 3 min as of the start of the trip and checks them for plausibility.
The smallest pressure value on each axle is then stored as the new specified value for pressure monitoring.
With new wheels or a longer parking time of t greater than 19 min the vehicle's own wheel detection and axle assignment via wheel sensors must be concluded.
A new wheel sensor is monitored after a trip of approx. t = 10 min.
Automatic fill detection function sequence (except code (494) USA version)
Automatic fill detection takes place if a pressure change of more than p = 0.2 bar has been detected in at least 2 wheels.
Temperature-compensated and filtered pressure values can be used here for comparison.
The new reference values are stored if the plausibility check is passed.
Learn mode function sequence
The learn mode is comprised of the following subfunctions:
^ Function sequence for determination of new specified pressures
^ Function sequence for wheel position identification (with code (476) Tire pressure monitor (premium))
^ Function sequence for learn mode in workshops
Function sequence for determination of new specified pressures
Manual setting of new specified pressures is performed by manually restarting the TPM [RDK] system in the instrument cluster.
The specified pressures are determined on an axle by axle basis.
On vehicles with code (494) USA version, new specified pressures are only set after a manual restart. In other countries, new specified pressures are set automatically after filling detection.
Function sequence for wheel position identification (with code (476) Tire pressure monitor (premium))
After a parking time of at least t = 20 min, the TPM [RDK] control unit activates the left front TPM wheel antenna (A2/44) and right front TPM wheel antenna (A2/45) after the start of a trip.
First the signal is transmitted by the left front TPM wheel antenna until a corresponding radio telegram from the left front wheel sensor is received as an answer by the TPM [RDK] control unit via the TPM central antenna.
After this the signal is transmitted by the right front TPM wheel antenna until a corresponding radio telegram from the right front wheel sensor is received as an answer by the TPM [RDK] control unit via the TPM central antenna.
The procedure is repeated 2 more times. As a result the TPM [RDK] control unit can clearly assign identification numbers of the front wheel sensors to a position.
The rear wheels are assigned with the aid of the radial acceleration transmitted by the respective rear wheel sensor and the differences in wheel speed when cornering.
The steering angle when cornering is recorded by the steering angle sensor (N49) and transmitted by the steering column tube module via the chassis CAN to the central gateway control unit. This passes on the signal to the TPM control unit via the interior CAN.
After a trip with many curves the wheel assignment at the rear axle can be concluded in this way.
After new wheels are mounted the pressure picture is displayed as soon as position identification of the front wheels is complete. The position of the rear wheels is not yet reliably identified at this point and is corrected later if necessary.
Function sequence for learn mode in workshops
Working with the Diagnosis Assistance System (DAS) or CANDI: New wheel sensors can be taught-in with the routine "Check for WU Remeasure transponder". With this routine it is possible to select 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 the Trigger tool, the respective wheel sensor must be triggered. The wheel sensor then transmits a telegram and the wheel identifier is read out from this.
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".
For teach-in via pressure change, the pressure at the corresponding wheel must be changed by p = 0.3 bar. As a result of this the wheel sensor transmits telegrams with the changed pressure value to the TPM [RDK] control unit. The wheel identifier is read out from these telegrams.
The result is queried with the service "Check for WU Remeasure Transponder: Request results WU ID". The detected wheel identifiers must then be written to the respective position by the user 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 performs a plausibility check on the wheel identifiers whereby all wheels must have different wheel identifier numbers. After at least one telegram has been received from each wheel, the pressure display appears in the instrument cluster.
