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

GF40.15-P-0002Q Tire pressure loss warning (RDW), function
- with CODE (477) Tire pressure loss warning


The tire pressure loss warning (RDW) is realized by the ESP and BAS control unit (N47-5). It manages without additional components. In the event of a tire pressure loss it should warn the driver before the tire is damaged due to running when flat. The warning takes place via the multifunction display (A1p13) in the instrument cluster (A1).

The function of the tire pressure loss warning is partially restricted in the following situations:
^ Snow chains fitted or winter road conditions
^ Loose substrate (sand, gravel etc.)
^ Sporty driving style (high cornering speed, hard acceleration)
^ Heavy loading of the vehicle
^ Trailer operation

Reactivate tire pressure loss warning
The tire pressure loss warning must be reactivated if the tire pressure has been changed.

When circuit 15 is switched on activation takes place by means of the right multifunction steering wheel button group (S111) and left multifunction steering wheel button group (S110). The corresponding displays appear in the multifunction display. The teach-in phase takes place after the reactivation. The relative rolling circumferences are taught in 6 different speed intervals. The tire pressure loss warning is not active in this learning process. The adaptation of the individual intervals takes approx 10 min/interval. As of this point in time the wheel speeds of the left front to right rear tires and right front to left rear tires are compared in each case.

Function requirements:
^ Vehicle speed greater than 20 km/h

Function
The rolling circumference depends on tire pressure. This dependency is evaluated by a comparison of the 4 wheel speeds by means of the rpm sensors (1-6/1, 1-6/2, L6/3 and 1-6/4) by the ESP control unit.

The ESP control unit compares:
^ Left front and right rear wheel speeds
^ Right front and left rear wheel speeds

Furthermore the following values are included in the computation at the same time:
^ Lateral acceleration and turn rate of the vehicle
(determined by the yaw rate and lateral acceleration sensor (B24/15))
^ Wheel torque
(determined by the ME control unit (N3/10) on gasoline engine or CDI control unit (N3/9) on diesel engine)

In the event of a pressure loss being detected the corresponding display takes place in the multifunction display.

Limits of the system
^ Warning limit in the event of a pressure loss of 30 % to 50 % at a wheel
^ Warning without stating position
^ No detection of even diffusion losses
^ Incorrect operation by the driver (reactivation despite significantly reduced pressure)