Tire pressure loss warning (RDW), function - GF40.15-P-0002FLM

MODEL 212 as of model year 2014 with CODE 477 (tire pressure loss warning system) 

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/s  ² 

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 (A1). The tire pressure loss warning is integrated into the Electronic Stability Program control unit (N30/4) (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles), except hybrid), or in the Premium Electronic Stability Program control unit (N30/7) (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles), except Hybrid) or in the regenerative braking system control unit (N30/6) (for hybrid).

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), except hybrid) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles), except hybrid) or the regenerative braking system control unit (for hybrid) evaluates the signals of 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. Switching on circuit 15 is detected by the electronic ignition lock control unit and the status is sent over chassis CAN 1 (CAN E1) to the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles), except hybrid) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles), except hybrid) or the regenerative braking system control unit (for hybrid).

The Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles), except hybrid) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles), except hybrid) or the regenerative braking system control unit (for hybrid) then receives the data from the yaw rate sensor for lateral and longitudinal acceleration over the dynamics CAN (CAN H) and reads in the signals from 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 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 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), the electronic stability program (ESP) or the regenerative braking system control unit (RBS)

Driver information, function sequence 

A warning is issued as of a pressure loss of approx. 30 to 50% at one wheel. The driver information is displayed via the instrument cluster.

The Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS), except CODE 990 (AMG vehicles), except hybrid) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS) or with CODE 990 (AMG vehicles), except hybrid) or the regenerative braking system control unit (for hybrid) sends the status of the tire pressure loss warning over chassis CAN 1 and chassis CAN 2 (CAN E2) with the front SAM control unit with fuse and relay module interface 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 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).