Tire pressure loss warning (RDW), function

GF40.15-P-0002CA

Tire pressure loss warning (RDW), function

22.3.13

MODEL	207.3/4
	up to model year 2014
	with CODE 477 (Tyre 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/s2

 The electronic ignition lock control unit makes available the circuit status of circuit 15 (N73) on the chassis CAN (CAN E).

General function sequence of tire pressure loss warning system

The tire pressure loss warning system detects a significant pressure loss on a tire and then issues a warning message in the multifunction display (A1p13) of the instrument cluster (A1). The tire pressure loss warning system is functionally integrated into the Electronic Stability Program control unit (N30/4) (except CODE 233 (DISTRONIC PLUS)) or into the Premium Electronic Stability Program 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 (except CODE 233 (DISTRONIC PLUS)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS)) evaluates the signals from the following components to detect any tire pressure loss:

– Yaw rate sensor for lateral and longitudinal acceleration (B24/15)

– 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)

A loss in tire pressure is detected from the rolling circumference of the tires, as the rolling circumference depends on the tire inflation pressure. The Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS)) reads in the signals from the rpm sensors directly and evaluates any differences in speed. The lateral acceleration and longitudinal acceleration of the vehicle are also included in the computation. To this end, the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS)) or the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS)) reads in the signals from yaw rate sensor for lateral and longitudinal acceleration.

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 a hardware fault is detected (e.g. in the Electronic Stability Program control unit (without CODE 233 (DISTRONIC PLUS)), sensor failure), the tire pressure loss warning system is shut down

- Sporty driving style (high cornering speed, hard acceleration)

- Snow chains fitted or winter road conditions

- Loose substrate (sand, gravel etc.)

- During control intervention functions by the antilock brake system (ABS), acceleration skid control (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 multifunction display in the instrument cluster.

The Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS)) or the Premium Electronic Stability Program 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 until the tire pressure loss warning system is restarted. The tire pressure loss warning 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 system is activated via the left multifunction steering wheel button group (S110) and the right multifunction steering wheel button group (S111). This request is read in by the steering column tube module control unit (N80) and sent to the instrument cluster via the chassis CAN.

The instrument cluster then sends the restart request to the Electronic Stability Program control unit (except CODE 233 (DISTRONIC PLUS)) or to the Premium Electronic Stability Program control unit (with CODE 233 (DISTRONIC PLUS)). The teach-in phase takes place after the restart. Here the relative rolling circumferences of the tires undergo teach-in in 7 different speed intervals (between v = 15 and 250 km/h).

The tire pressure loss warning (RDW) system is not active during the learn mode. Uniform pressure loss at all 4 tires (e.g. due to diffusion) cannot be detected. Incorrect operation (e.g. tire pressure loss warning restart at significantly too low tire inflation pressure) are not detected either.

	Electrical function schematic for tire pressure loss warning (RDW) system		PE40.15-P-2051-97EAA
	Tire pressure loss warning (RDW), location of components		GF40.15-P-0002-01CA
	Tire pressure loss warning (RDW), block diagram		GF40.15-P-0002-02CA
	Tire pressure loss warning (RDW) Mercedes-Benz Driver Information Service		GF40.15-P-0002-03CA
	Overview of components in tire pressure loss warning (RDW) system		GF40.15-P-9997CA