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 rotational speed sensors of the wheels and evaluates any differences in rotational speed. 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 ESP® control unit, sensor failure), the tire pressure loss warning 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) | ||
Function schematics | |||
Function schematic for tire pressure loss warning (RDW) | Model 118, 177, 247 with code 477 (Tire pressure loss warner)Model 167 with code 477 (Tire pressure loss warner) | ||
Model 213, 238, 257, 290 as of model year 2021 with code 477 (Tire pressure loss warner) |