MODEL | 218 |
up to model year 2014 | |
with CODE 477 (tyre pressure loss warning system) |
A1 | Instrument cluster |
A1p13 | Multifunction display |
B24/15 | Yaw rate, lateral and longitudinal acceleration sensor |
CAN E | Chassis CAN |
CAN H | Vehicle dynamics CAN |
L6/1 | Left front axle rpm sensor |
L6/2 | Right front axle rpm sensor |
L6/3 | Left rear axle rpm sensor |
L6/4 | Right rear axle rpm sensor |
LIN E1 | Steering LIN |
N30/4 | Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) |
N30/7 | Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) |
N73 | Electronic ignition switch control unit |
N80 | Steering column module control unit |
N135 | Steering wheel electronics |
S110 | Left multifunction steering wheel button group |
S111 | Right multifunction steering wheel button group |
P40.15-2460-81
Function requirements, general
Status "Circuit 15 ON"
Tire pressure loss warning (RDW) is functional
Vehicle speed v > 15 km/h
Lateral acceleration and longitudinal acceleration a < 1 m/s2
The "circuit 15 ON" status is sent by the electronic ignition lock control unit to the chassis CAN.
General function sequence of tire pressure loss warning system
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. The tire pressure loss warning function is integrated into the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or in the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)).
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 (except CODE (233) DISTRONIC PLUS, except CODE (990) AMG vehicles) or the Premium Electronic Stability Program control unit (with CODE (233) DISTRONIC PLUS or with CODE (990) AMG vehicles)) evaluates the signals of the following components to enable any tire pressure loss to be detected:
– Left front axle rpm sensor
– Right front axle rpm sensor
– Left rear axle rpm sensor
– Right rear axle rpm sensor
– Yaw rate, lateral and longitudinal acceleration sensor
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. Switching on circuit 15 is detected by the electronic ignition lock control unit, and the status is sent over the chassis CAN to the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or to the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)). The Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) then receives the data from the yaw rate sensor for lateral and longitudinal acceleration over the dynamics CAN and reads in the signals of the rpm sensors directly.
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°)
– If hardware faults are detected (e.g. in the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles), except hybrid)), sensor malfunctions) the tire pressure loss warning is shut down
- Sporty driving style (high cornering speed, hard acceleration)
- Snow chains fitted or winter road conditions
- Loose substrate (sand, gravel etc.)
- The RDW 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)
Driver information, function sequence
A warning is issued as of a pressure loss of approx. 30 to 50 % at one wheel. Driver information is shown on the instrument cluster.
The Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles)) sends the status of the tire pressure loss warning over 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 until the tire pressure loss warning system is restarted.
The tire pressure loss warning (RDW) system must be restarted in the operating menu in the instrument cluster using the left multifunction steering wheel button group and right multifunction steering wheel button group 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 circumference of the tires undergoes teach-in up to 7 different speed intervals (in a range from 15 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).