Tire Pressure Loss Warning System, Basic Function - GF40.15-P-1001A

Model All (CAR) with code 477 (Tire pressure loss warner) 

Overview 

This document contains information on:

• General 
• Function requirements 
• Function 
  • Learning process 

General 

The tire pressure loss warning system (RDW) detects a significant pressure loss in the tires and issues a warning via the instrument cluster.

Function requirements 

• Ignition ON (circuit 15)
• Longitudinal acceleration < 1 m/s²
• Lateral acceleration < 1 m/s²

Function 

Tire pressure loss is detected based on the rolling circumference of the tires; the rolling circumference is dependent on the tire pressure.

The Electronic Stability Program (ESP®) control unit reads in the signals from the rotational speed sensors of the wheels and evaluates any differences in rotational speed. The tire pressure loss that has occurred is calculated on the basis of this data and, if required, a warning without specification of the position is output via the instrument cluster. A warning is issued from a pressure loss of approx. 30 to 50 % in one tire.

Operation of the tire pressure loss warning system may be restricted in the following situations:

• In high-bank curves or on roads with a great lateral incline (incline angle > 7°).
• If hardware faults are detected (e.g. in the ESP® control unit, sensor failure), the tire pressure loss warning is shut down.
• Sporty driving style (high cornering speed, hard acceleration).
• Snow chains fitted or winter road conditions.
• On loose ground (sand, gravel, etc.).
• With control intervention functions by the anti-lock braking system (ABS), anti-slip control (ASR) or Electronic Stability Program (ESP®).
• In the event of pressure loss in more than one wheel.

Learning process 

The tire pressure loss warning system can be restarted in the control menu. The teach-in process is performed after the restart. Here, the relative rolling circumferences of the tires are taught-in in up to 7 different speed intervals between 15 and 250 km/h. The RDW is inactive during the teach-in process. Uniform pressure loss at all 4 tires (e.g. due to diffusion) cannot be detected. Incorrect operation (e.g. tire pressure loss warning restarted when the tire pressure is much too low) is not detected either.

	Function schematics
	Function schematic for tire pressure loss warning (RDW)	Model 118, 167, 177, 247	PE40.15-P-2501-97A
		Model 213, 238, 257, 290 as of model year 2021	PE40.15-P-2501-97B
		Model 206, 214, 223, 236, 254	PE40.15-P-2501-97C
	Additional basic functions
	Electronic Stability Program, basic function		GF42.45-P-1002A