GF40.15-P-0002RC Tire Pressure Loss Warning (RDW), Function
GF40.15-P-0002RC Tire pressure loss warning (RDW), function
- with CODE (477) Tire pressure loss warning
Function requirements general
^ Circuit 15 On
^ Tire pressure loss warning (RDW) system is functional
^ Vehicle speed v > 20 km/h
^ Lateral acceleration and longitudinal acceleration a < 1 m/s2
Tire pressure loss warning (RDW) system in general
The tire pressure loss warning (RDW) system detects a significant pressure loss at a tire and then displays a warning message in the instrument cluster (A1). The tire pressure loss warning (RDW) system is functionally integrated into the ESP and BAS control unit (N47-5)
The tire pressure loss warning (RDW) system is made up of the following subfunctions:
^ Function sequence of tire pressure loss detection
^ Function sequence for driver information
Function sequence of tire pressure loss detection
The ESP and BAS control unit evaluates signals from the following components to enable detection of tire pressure loss:
- Left front rpm sensor (L6/1)
- Right front rpm sensor (L6/2)
- Left rear rpm sensor (L6/3)
- Right rear rpm sensor (L6/4)
- Micromechanical turn rate sensor AY pickup (B24/15)
The rolling circumference is used as the basis for tire pressure loss detection. The rolling circumference depends on the tire pressure. The wheel speeds are compared with each other and evaluated accordingly.
The lateral acceleration, the longitudinal acceleration and the individual wheel speeds are included in the calculation. Activation of circuit 15 is detected by the EZS control unit (N73) and the status is sent to the ESP and BAS control unit via the engine compartment CAN.
The ESP and BAS control unit then reads in the data of the yaw rate, lateral and longitudinal acceleration sensor and the rpm sensor.
The function of the tire pressure loss warning (RDW) system is partially restricted in the following situations:
- On high-bank curves or on roads with a heavy lateral incline (typically > 7 degrees)
- In the event of hardware fault detection (e.g. in the ESP and BAS control unit, sensor failure), the tire pressure loss warning (RDW) system is deactivated.
- Sporty driving style (high cornering speed, hard acceleration)
- Snow chains fitted or winter road conditions
- Loose substrate (sand, gravel etc.)
- With control intervention functions by the antilock brake system (ABS), acceleration slip regulation (ASR) or electronic stability program (ESP)
Function sequence for driver information
A warning is issued as of a pressure loss of approx. 30 to 50% at one wheel. Driver information is shown on the upper multifunction display (A1p13) in the instrument cluster.
The ESP and BAS control unit sends the status of the tire pressure loss warning (RDW) system to the instrument cluster via the engine compartment CAN. The instrument cluster then outputs an appropriate message.
A warning without position specification is only output after the vehicle has been driven for a few minutes. In the subsequent ignition sequences, a reminder message is displayed, provided that the tire pressure loss warning (RDW) system has not been restarted.
The tire pressure loss warning (RDW) system has to be restarted in the instrument cluster's control menu, if one or more tires are changed or the tire inflation pressures are changed. This erases any pending warning messages.
The left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111) are used for activation. This request is read in over the local interconnect network (LIN) from the steering column module (N80) and sent over the engine compartment-CAN to the instrument cluster.
The instrument cluster then sends the request for a restart to the ESP and BAS control unit.
The teach-in phase takes place after the restart. The relative rolling circumferences of the tires are taught in during up to seven different speed intervals (between v = 15 km/h and 250 km/h). The tire pressure loss warning (RDW) system is not active in this learning process.
Uniform pressure loss at all four tires (e.g. due to diffusion) cannot be detected.
Incorrect operation by the driver cannot be detected (e.g. restart of the tire pressure loss warning (RDW) system with extremely low tire inflation pressure).
