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

GF40.15-P-0002R Tire pressure loss warning (RDW) function
- with CODE (477) Tire pressure loss warning
- as of 1.6.04 up to model year 08

General
The tire pressure loss warning (RDW) is a system scope of the ESP, SPS [PML] and BAS control unit (N47-5). It gets by without additional components It should warn the driver in the event of a tire pressure loss, before roll-flat damage occurs due to excessive flexing energy at the tire.

The driver is warned about a pressure loss via the left (A1p13) and right (A1p15) multifunction displays in the instrument cluster (A1). The tire pressure monitor warning lamp (A1e66) in the instrument cluster is actuated in parallel with this.

Function
The rolling circumference depending on the tire pressure. This dependency is evaluated in the ESP, SPS [PML] and BAS control unit by a comparison of the 4 wheel rpm.
The ESP, SPS [PML] and BAS control unit compares between:
^ FL and RR wheel rpm
^ FR and RL wheel rpm

Furthermore, the following sensor signals are incorporated in the calculation at the same time:
^ Lateral acceleration
^ Yaw rate
^ Wheel torque

Aim
A tire pressure loss should be detected at a wheel before this pressure loss leads to damage to the tire.

The tires are monitored by the tire pressure loss warning (RDW) without specifying the position.

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

The tire pressure loss warning can be coded via STAR DIAGNOSIS to "tire pressure loss warning present" or "tire pressure loss warning not present". On vehicles which have tire pressure monitor (code 475) as special equipment, the tire pressure loss warning is set to "...not present".

System properties:
^ Detection of pressure loss after driving for a few minutes
^ Active when driving straight ahead (lateral acceleration < 1 m/s2).
^ Active during uniform journey (longitudinal acceleration < 1 m/s2).
^ Not active with control intervention function (ABS, ASR, ESP).
^ Not active with large drive torque.
^ Not active when braking
^ Partially active at a low coefficient of friction, on a rough road and when chains are fitted

System limits:
^ Warning limit with a pressure loss of 30 to 50% at one wheel
^ Warning without stating position
^ No detection of even diffusion losses
^ Incorrect operation by the driver (reactivation despite significantly reduced pressure)