GF40.15-P-0001RC Tire Pressure Monitor Function
GF40.15-P-0001RC Tire pressure monitor function
- with CODE (470) Tire pressure monitor (base) Fa. Schrader
Function requirements, general
^ Circuit 15 On
^ Tire pressure monitor (TPM [RDK]) system functional
TPM [(RDK)] system in 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 6.375 bar.
The TPM [RDK] comprises the following subfunctions:
^ 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 journey the TPM [RDK] system continuously monitors the tire pressure of all rotating wheels (with circuit 15 OFF run-on time of t = 19 min).
During a journey 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 data telegrams every t = 60 s. These data telegrams contain the pressure, tire pressure temperature, individual serial number and status information (manufacturer, direction of rotation, operating mode etc.). The data are conveyed via two-way radio to the TPM [RDK] control unit (N88). Axle localization is performed by evaluating the reception level of the wheel sensors. Side localization is based on the right/left information of the wheel sensors.
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 vehicle speed is transmitted by the instrument cluster (A1). The outside temperature is measured by the outside temperature display temperature sensor (B14) and is transmitted by the driver-side rear SAM control unit with fuse and relay module (N10/1).
Any warning messages and menu displays are shown on the upper multifunction display (A1p13) in the instrument cluster.
Warning message function sequence
A warning message is issued when a relevant loss of pressure has been detected in at least one of the tires. The warning message is issued without any position data.
The driver receives the feedback via the upper multifunction display or via the tire pressure monitor warning lamp (A1e66).
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
A soft warning message is issued immediately after a journey 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 from p > 0.25 bar
If the tire pressure of one wheel is continuously under the warning threshold for t = 12 min during a trip, a warning signal is set, stored in the memory of the TPM [RDK] control unit and displayed in the instrument cluster at the end of the trip (circuit 15 OFF).
If the tire pressure increases again to more than p = 0.1 bar under the stored specified value, the warning message is suppressed.
Cancelation of warning message:
- Warning threshold no longer dropped below
- Successful automatic fill detection
- Manual restart
Hard warning message function sequence
While driving, the hard warning message informs the driver of any significant, safety-relevant pressure loss.
Warning threshold:
- Pressure loss of 20% or p ≥0.5 bar
In the event of a pressure drop below the warning threshold, a warning message is displayed in the upper multifunction display after t = 5 min at the latest and the tire pressure monitor warning lamp is actuated. If the pressure loss is very high (p ≥0.2 bar under warning threshold), the warning message is issued after max. t = 1 min.
If a leak is detected (air extraction p > 0.2 bar/min) the driver is notified with a warning message "Warning! Tire defect".
The tire pressure monitor warning lamp is actuated together with a hard warning message, which is repeated during the next ignition sequence.
Cancelation of warning message:
- 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 message is triggered, even before the triggering criterion for the hard warning message is reached. The warning message 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 (red) "Warning! Tire defect" on the upper multifunction display in the instrument cluster.
Cancelation of 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 TPM [RDK] 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 submenu for restarting the TPM [RDK] system can be accessed via the trip odometer reset button (A1 s3).
The signals are read in by the steering column module (N80) over the local interconnect network (LIN) and then transmitted over the interior CAN to the instrument cluster. The pressure thresholds for the warning messages 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 = 5 min as of the start of the journey and checks them for 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 - at the start of a journey - a change in pressure of more than p = 0.2 bar was detected on at least two of the 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.
Learn mode function sequence
With new wheels or a longer parking time of t > 20 min, the separate wheel detection and axle assignment must be completed first via the wheel sensors.
A new wheel sensor is taught in with a new identification number and monitored after approx. t = 10 min. Side localization is based on the right/left information of the wheel sensors.
