GF40.15-P-0002FL Tire Pressure Loss Warning (RDW), Function
GF40.15-P-0002FL Tire pressure loss warning (RDW), function
- with CODE (477) Tire pressure loss warning
Function requirements, general
^ Circuit 15 On
^ Tire pressure loss warning (RDW) is functional
^ Vehicle speed v greater than 15 km/h
^ Lateral acceleration and longitudinal acceleration a less than 1 m/s2
Function sequence for tire pressure loss warning 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 system is functionally integrated into the Electronic Stability Program control unit (N30/4) (without code (233) DISTRONIC PLUS) or in Electronic Stability Program Premium control unit (N30/7) (with code (233) DISTRONIC PLUS).
The RDW comprises the following subfunctions:
^ Function sequence of tire pressure loss detection
^ Function sequence for driver information
Function sequence of tire pressure loss detection
The Electronic Stability Program control unit (without code (233) DISTRONIC PLUS) or the Electronic Stability Program Premium control unit (with code (233) DISTRONIC PLUS) evaluates the signals from the following components to detect any tire pressure loss:
- Left front axle rpm sensor (L6/1)
- Right front axle rpm sensor (L6/2)
- Left rear axle rpm sensor (L6/3)
- Right rear axle rpm sensor (L6/4)
- Yaw rate sensor for lateral and longitudinal acceleration (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. When circuit 15 is switched on, it is detected by the electronic ignition lock control unit (N73) and the status is sent over the chassis CAN (CAN E) to the Electronic Stability Program control unit (without code (233) DISTRONIC PLUS) or to the Electronic Stability Program Premium control unit (with code (233) DISTRONIC PLUS). The Electronic Stability Program control unit (without code (233) DISTRONIC PLUS) or the Electronic Stability Program Premium control unit (with code (233) DISTRONIC PLUS) then receives the data from the yaw rate sensor for lateral and longitudinal acceleration over the vehicle dynamics CAN (CAN H) and directly reads-in the signals from the rpm sensors.
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 greater than 7 degrees)
- If a hardware fault is detected (e.g. in the Electronic Stability Program control unit (without code (233) DISTRONIC PLUS), sensor failure) the system is shut down
- Sporty driving style (high cornering speed, hard acceleration)
- Snow chains fitted or winter road conditions
- Loose substrate (sand, gravel etc.)
- The tire pressure loss warning is only active during forward travel. The function is temporarily removed from display during reverse travel
- During control intervention functions by the antilock brake system (ABS), acceleration skid control (ASR) or electronic stability program (ESP)
Function sequence of 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 multifunction display (A1p13) in the instrument cluster.
The Electronic Stability Program control unit (without code (233) DISTRONIC PLUS) or the Electronic Stability Program Premium control unit (with code (233) DISTRONIC PLUS) transmits the status of the tire pressure loss warning over the chassis CAN to the instrument cluster, which then issues a corresponding 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 must be restarted in the operating menu in the instrument cluster via the left multifunction steering wheel button group (S110) and right multifunction steering wheel button group (S111) after one or more tires have been changed or the tire pressures have been adjusted. This erases any pending warning messages.
The teach-in phase takes place after the restart. The relative rolling circumferences of the tires is taught-in during up to 7 different speed intervals (in a range from 15 km/h to 250 km/h). The tire pressure loss warning is not active in this learning process. Uniform pressure loss at all 4 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).
