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

Model all (CAR) with code 477 (tire pressure loss warning system) 

Overview 

This document contains information on:

• General 
• Function requirements 
• Tire pressure loss warning 
• Learning process 

General 

The tire pressure loss warning system detects a significant loss in pressure at the tires and outputs a warning via the instrument cluster.

Function requirements 

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

Tire pressure loss warning 

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 rpm sensors and evaluates any differences in rpm. 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 as of a pressure loss of approx. 30 - 50% at one tire.

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

• On high-bank curves or on roads with a large lateral incline (incline angle > 7°)
• If hardware faults are detected (e.g. in the Electronic Stability Program control unit, 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
• On loose substrate (sand, gravel, etc.)
• With control intervention functions by the anti-lock braking system (ABS), acceleration skid control (ASR) or Electronic Stability Program (ESP®)
• For pressure losses at 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 undergo teach-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.

	Additional basic functions
	Electronic Stability Program, basic function	Model all (CAR) with code 477 (tire pressure loss warning system)	GF42.45-P-1002A
	Function schematics
	Function schematic for tire pressure loss warning (RDW)	Model 177 with code 477 (tire pressure loss warning system)	PE40.15-P-2501A