GF40.15-P-0001CA Tire Pressure Monitor Function
GF40.15-P-0001CA Tire pressure monitor function
- with CODE (475) Tire pressure monitor (premium) Fa. Schrader
General function requirements
^ "Circuit 15 ON" status
The circuit 15 status is sent by the electronic ignition lock control unit (N73) to the chassis CAN (CAN E).
Tire pressure monitor (TPM [RDK]) general
The TPM [RDK] system monitors the air pressure in the tires and by doing so contributes to active safety. A previously stored specified pressure is used as a comparative value. In the event of a relevant pressure loss, a warning message is shown on the multifunction display (A1p13) in the instrument cluster (A1).
The measuring range of the TPM [RDK] systems extends from p = 0 to 6.375 bar.
The TPM [RDK] comprises the following subfunctions:
^ Function sequence for recording tire pressure
^ Function sequence for displaying warning messages
^ Manual restart function sequence
^ Automatic fill detection function sequence
^ Learn mode function sequence
Function sequence for recording tire inflation pressure
During a journey the TPM [RDK] system continuously monitors the tire inflation pressure (run-on time for "circuit 15 OFF" status, for t = 19 min.).
The left front tire pressure sensor (A69/1), right front tire pressure sensor (A69/2), left rear tire pressure sensor (A69/3) and the right rear tire pressure sensor (A69/4) send every t = 60 s data telegrams to the control unit tire pressure monitoring (N88). The following information is contained in these data telegrams:
- Tire inflation pressure
- Tire inflation pressure temperature
- Serial number and status information (e.g. manufacturer, direction of rotation, operating mode)
This information is sent by radio by the control unit tire pressure monitoring system. Axle localization is conducted by evaluating the reception level and the side localization by evaluating the direction of rotation information for the tire pressure sensors.
The outside temperature and vehicle speed are also taken into consideration when displaying warning messages. The outside temperature is recorded by the outside temperature sensor (B14). The front SAM control unit with fuse and relay module (N10/1) reads in the signals from the outside temperature sensor and sends this over the interior CAN (CAN B) to the instrument cluster. The instrument cluster evaluates these signals and sends them along with information on vehicle speed to the control unit tire pressure monitoring over the chassis CAN. Information on vehicle speed is also sent by the instrument cluster over the chassis CAN.
Function sequence for displaying warning messages
The control unit tire pressure monitoring system continuously evaluates the data telegrams of the tire pressure sensors.
If a relevant loss of pressure is detected at a tire, the control unit tire pressure monitoring sends the request to display a warning message over the chassis CAN to the front SAM control unit. The front SAM control unit forwards this request over the interior CAN to the instrument cluster. The instrument cluster issues a warning message through the multifunction display and actuates the tire pressure monitor warning lamp (A1e66).
The issue warning messages function is made up of the following component functions:
^ Function sequence for displaying soft warning
^ Function sequence for displaying hard warning
^ Function sequence for displaying leak detection (rapid pressure loss)
Function sequence for displaying soft warning
A soft warning is displayed for a pressure loss of [triangle]p greater than 0.25 bar on a tire immediately after a journey ends ("circuit 15 OFF" status).
The soft warning message display notifies the driver in good time, that a tire pressure needs to be corrected. If the tire inflation pressure of a tire is continuously below the warning threshold for t = 12 min. during a trip, a warning signal is set, stored in the tire pressure monitoring control unit memory and shown on the multifunction display at the end of the trip ("circuit 15 OFF" status). If the tire pressure increases again to at least [triangle]p = 0.1 bar under the stored specified value, the soft warning message is suppressed.
Warning cancellation:
- Value is no longer below warning threshold
- Successful automatic fill detection
- Manual restart
Function sequence for displaying hard warning
A hard warning is displayed for a pressure loss of 20 % or [triangle]p ≥ 0.5 bar (warning threshold) on a tire and informs the driver of a significant, safety relevant pressure loss.
If the pressure loss exceeds the warning threshold of [triangle]p ≥ 0.5 bar, a warning message is shown after no more than t = 5 min. in the multifunction display, and the tire pressure monitor warning lamp is actuated. If the pressure loss is very high ([triangle]p ≥ 2 bar below the warning threshold), the warning message is issued after t = 1 minute at the latest.
If a leak is detected (air release [triangle]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 and it is repeated for 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. At no later than t = 120 s after recognition of a pressure loss of [triangle]p = 0.2 bar/min., the multifunction display shows the "Caution: Tire defect" warning message.
During an ignition sequence, the warning message can be canceled by successful filling detection or by a manual restart.
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 the start of a journey new pressure values exist and no warning criterion is met, the tire pressure monitoring warning lamp is switched off and the warning message is cleared.
Manual restart function sequence
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 (S110) and the right multifunction steering wheel button group (S111) can be used to scroll through the TPM [RDK] menu in the instrument cluster. The Reset and "Back" (S110s7) button can be used to enter the submenu for restarting the tire pressure monitor system.
The steering column tube module (N80) reads in the multifunction steering wheel button group signals over the steering LIN (LIN E1) and forwards them over the chassis-CAN (CAN C) 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 smallest pressure value on each axle is then stored as the new specified value for pressure monitoring.
Automatic fill detection function sequence
Automatic fill detection is performed if a change in pressure of more than [triangle]p greater than 0.2 bar was detected on at least two of the 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
Where new wheels are concerned or where a vehicle has been stationary for t greater than 20 min. the automatic wheel detection and axle assignment have to be disconnected first over the tire pressure sensor.
A new tire pressure sensor undergoes teach-in in with a new identification number and is monitored after approx. t = 10 min. Side localization is based on the right and left information from the tire pressure sensors.
When conducted in workshops, the function sequence for the learn mode is split up into the following component functions:
^ Work conducted with the Diagnosis Assistance System (DAS)
^ Work conducted with the E-Tester or CANDI
Work conducted with the DAS
The learn mode can be conducted in workshops with the DAS by entering the identification number. When working with DAS, follow the "Initial start-up" routine.
2 variants are available:
- "Initial start-up with unknown WHEEL IDs"
- "Initial start-up with known WHEEL IDs"
Work conducted with the E-Tester or CANDI
New tire pressure sensors can be taught in using the "Check for WU Remeasure Transponder" routine.
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, the respective tire pressure sensor must be triggered.
The tire pressure sensor then sends a data telegram, which can be used to read out the wheel identification number (wheel ID). For teach-in via pressure change, the pressure at the corresponding wheel must be changed by 0.3 bar. The tire pressure 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 detected wheel identification numbers must then be written to the respective position by the user in the diagnosis service "Download transmitter IDs" (Left Front, Right Front, Right Rear and Left Rear).
The "Download Axle/Side Location Status" service must also be written by pressing OK The control unit tire pressure monitoring checks the plausibility of the wheel identification numbers and does not permit any doubled-up wheel identification numbers. After at least one data telegram has been received from each wheel, the pressure display appears in the instrument cluster.
