GF40.15-P-0001FL Tire Pressure Monitor Function
GF40.15-P-0001FL Tire pressure monitor function
- with CODE (475) Tire pressure monitor (Premium) Fa. Schrader
Function requirements, general
^ "Circuit 15 ON" status
^ Tire pressure monitor (TPM [RDK]) system functional
The status of circuit 15 is supplied by the electronic ignition lock control unit (N73) over the chassis CAN (CAN E).
Tire pressure monitor, general
The TPM system supports the driver by monitoring the tire inflation pressure as of vehicle speed greater than 10 to 20 km/h (no stationary monitoring), thereby improving active safety.
The tire pressure monitoring system monitors the air pressure and temperature in the individual tires. A previously stored specified pressure (specified values) for each tire is used as the reference 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 subfunctions:
^ Tire pressure sensing function sequence
^ Warning message function sequence
^ Manual restart function sequence
^ Automatic fill detection function sequence, except code (494) USA version
^ Function sequence for learn mode in workshops or follow-up operations through entry of identification number using the Diagnosis Assistance System (DAS)
Tire pressure sensing function sequence
During a journey the TPM [RDK] system continuously monitors the tire pressure of all rotating wheels (with status "circuit 15 OFF" run on time of t = 19 min).
During a journey the left front tire pressure sensor (A69/1), right front tire pressure sensor (A69/2), left rear tire pressure sensor (A69/3) and right rear tire pressure 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 sent per radio frequency by the control unit tire pressure monitoring (N88).
Axle localization is performed by evaluating the reception level of the tire pressure sensors. Side localization is performed by evaluating the direction of rotation information.
In addition, the tire pressure monitoring control unit incorporates the outside temperature and the vehicle speed into the warning logic. The data are supplied over the chassis CAN.
The vehicle speed is transmitted by the instrument cluster (A1). The outside temperature is recorded by the outside temperature sensor (B14) and transmitted by the front SAM control unit with fuse and relay module (N10/1).
Any warning or information messages are shown in the multifunction display (A1p13) in 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 data.
The driver receives feedback on 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
A soft warning is issued immediately after a journey is ended (status "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.
The warning threshold is defined as follows:
- Pressure loss of p greater than 0.25 bar
If during a journey, the tire pressure on at least one wheel is continually below the warning threshold for a time frame of t = 12 min., an acoustic warning is set, filed in the tire pressure monitoring control unit memory, and displayed on the instrument cluster at the end of the trip ("circuit 15 OFF" status).
If the tire pressure increases again to at least p = 0.1 bar under the stored specified value, the warning message is suppressed. The warning message is retracted if one of the following events takes place:
- Value is no longer below warning threshold
- 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 tire pressure drops below the value specified by the warning threshold, then at the latest after t = 5 min. a warning message is shown in the multifunction display and the tire pressure monitor warning lamp is actuated. If the pressure loss is very high (p ≥ 0.2 bar below the warning threshold), the warning message is issued after t = 1 minute at the latest.
If a leak is detected (air release 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. The warning message is retracted if one of the following events takes place:
- Value is no longer below warning threshold
- Successful automatic fill detection, except code (494) USA version
- 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. The warning 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 on the multifunction display in the instrument cluster as a warning message "Warning! Tire defect".
The warning message is suppressed in the event of one of the following events occurring:
- Value is no longer below warning threshold
- Successful automatic fill detection, except code (494) USA version
- 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 call up and scroll through the TPM [RDK] menu in the instrument cluster. The OK (S110s6) button can be used to enter the submenu to restart the TPM [RDK] system.
The signals are read in by the steering column module control unit (N80) (LIN E1) over the steering LIN and then transmitted over the chassis 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 smallest pressure value on each axle is then stored as the new specified value for pressure monitoring.
Automatic fill detection function sequence, except code (494) USA version
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 2 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.
Function sequence for learn mode in workshops or follow-up operations through entry of identification number using the Diagnosis Assistance System
Where new wheels or an extended parking period of t greater than 20 min. is concerned, the automatic wheel detection and axle assignment have to be started using the tire pressure sensors at the end of a trip.
A new tire pressure sensor undergoes automatic teach-in after a journey of max. t = 10 min. Side localization is based on the right/left information of the tire pressure sensors.
During axle assignment the rear wheels that are closer to the receiver are received more powerfully than the further removed front wheels.
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".
When working with the E-Tester or CANDI, the "Check for WU Remeasure Transponder" routine enables new tire pressure sensors to undergo teach-in. 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 transmits a data telegram which is used to read out the wheel identifier.
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 identifier is read out from these data telegrams.
The result is queried with the service "Check for WU Remeasure Transponder: Request results WU D". 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.
