Basic Function Of Tire Pressure Loss Detection System - GF40.15-P-9900A

Model All (4xWD, CAR) 

Overview 

This document contains information on:

• General 
• Function 
  • Indirect measuring procedure 
  • Direct measuring procedure 

General 

The tire pressure loss warning system monitors and continuously checks the given tire pressure during vehicle operation. If a pressure drop occurs in the wheel and tire assemblies, a warning is issued via the driver's display.

Function 

The tire pressure loss warning system detects a significant pressure loss at the tires. Before damage to the tire occurs, the driver is informed via a message in the driver's display. Among other elements, the signals of the rotational speed sensors evaluated by the ESP® control unit serve as the output parameter for determining the tire pressure loss. In contrast to the tire pressure monitoring system, the tire pressure loss warning system is an indirect measurement system.

Indirect measuring procedure 

In the indirect measuring procedure, the tire pressure is read out via the rotational speed sensors of the ABS. These detect a change in tire diameter when the tire pressure decreases, in which case the rotational speed of the affected wheel and tire assembly increases in relation to the other. This increase in rotational speed is then interpreted as a pressure drop.

Direct measuring procedure 

The tire pressure monitoring system monitors the air pressure in the individual tires by comparing the measured pressure with a previously stored reference pressure. With this direct measuring procedure, the tire pressures are measured directly via sensors in the valves of the wheel and tire assemblies. This allows the exact tire pressure from each wheel and tire assembly to be read out via the instrument cluster.

	Additional basic functions
	Tire pressure monitoring system, basic function	Model all (CAR) with code 475 (Tire pressure monitor (TPM))	GF40.15-P-1000A
	Tire pressure loss warning system, basic function	Model all (CAR) with code 477 (Tire pressure loss warner)	GF40.15-P-1001A