GF40.15-P-0002SX Tire Pressure Loss Warning (RDW), Function

GF40.15-P-0002SX Tire pressure loss warning (RDW), function
- except CODE (494) USA version [model 216.3, 221.1]
- with CODE (477) Tire pressure loss warning [model 221.1]

Component Identification:

General
The tire pressure loss warning (RDW) system is integrated in the ESP control unit. Additional components are not required. It is to warn the driver in the event of tire pressure loss before the tire runs flat due to puncture damage.

In the event of a pressure loss the driver is warned via the multifunction display (A1p13) in the instrument cluster. In a parallel operation the system activates the tire pressure monitor warning lamp in the instrument cluster.

Function
The rolling circumference depends on the tire inflation pressure and driving speed. The rolling circumference enlarges as the vehicle speed increases and the tire inflation pressure increases. This dependency is evaluated by a comparison of the four wheel speeds in the ESP control unit.

The ESP control unit compares:
^ Left front wheel speed (VL) and right rear wheel speed (HR)
^ Right front wheel speed (VR) and left rear wheel speed (HL)

As further driving dynamics variables, such the effect of slip or slip angle on the dynamic rolling circumference or with the effect of cornering on wheel speed mean that the following sensor signals are included the calculation:
^ Lateral acceleration
^ Turn rate
^ Wheel forces

Aim
This tire pressure loss warning system points out a possible tire pressure loss to the driver. Irreparable damage to the tire can thus be avoided by the timely use of a spare tire or of TIREFIT and its mobility maintained.

The tire pressure loss warning system monitors the tires without specifying the position of the wheels.

The tire pressure loss warning system is only active from a minimum speed of approx. 20 km/h.

System properties:
^ Warning limit with a pressure loss of 30 to 50% at one wheel
^ Detection of pressure loss after driving for a few minutes
^ Active when driving straight ahead (lateral acceleration less than 1 m/s2)
^ Active when driving uniformly (longitudinal acceleration less than 1 m/s2)
^ Inactive during control intervention function of Electronic Stability Program (ESP)
^ Inactive when drive torque is large
^ Inactive when braking
^ Partially active e.g. under rough road conditions, operating with snow chains
^ Warning without wheel position details
^ No detection of even diffusion losses

After each change of tire inflation pressure (e.g. pressure correction, tire replacement, wheel exchange) the new correct tire inflation pressure must be conveyed to the system. This happens with the help of the multifunction display in the instrument cluster and the buttons on the multifunction steering wheel.

On vehicles with code (475) Tire pressure monitor (Siemens) the tire pressure loss warning system in the ESP control unit is switched off. If a new ESP control unit is installed in a vehicle with code (475) Tire pressure monitor (Siemens), it is to be guaranteed that the RDW system is switched off.