Anti-lock Braking System (ABS)

The ABS system improves active safety by preventing the wheels from locking during braking. Wheel lock is extremely dangerous because the front wheels lose steering control, and skidding rear wheels can cause the vehicle to spin or swerve into the other lane.
The ABS system shortens the braking distance to a minimum under any specific conditions (driving straight, cornering, on asphalt, icy, or wet roads, etc.).
In principle, during every braking maneuver ABS must perform two functions, ensuring:
- directional stability on road surfaces of different types (asphalt, concrete) and in different conditions (icy, covered with mud, snow, or on wet roads)
- reliable steering control and vehicle maneuverability under these conditions
These requirements need significant comments.
ABS does not cancel the laws of physics. The system cannot prevent the consequences of braking performed with insufficient distance to the vehicle ahead, cornering at excessively high speed, or when there is a risk of hydroplaning. These consequences remain the driver's responsibility. The presence of ABS, which provides enhanced safety potential, should not encourage you to drive recklessly.

Driving Characteristics of a Vehicle with ABS

After starting the engine, the ABS warning lamp on the instrument panel goes out.
The system activates automatically only when the speed reaches approximately 8 km/h. When the speed drops below 3 km/h, ABS switches off, so theoretically the wheels may lock at the very last stage of braking; however, in practice this is no longer significant.
ABS performs regulation within fractions of a second. Pulsation of the brake pedal means that braking is under ABS control, in other words, that the driver is operating at the limit. In addition, the chattering noise caused by ABS operation reminds the driver to adjust speed to the actual driving conditions, which have changed due to a reduction in the coefficient of friction (or grip) between the tires and the road, for example due to ice.
On roads with a loose layer (for example, gravel or snow) over a base with good grip, the braking distance may be longer than with locked wheels. This also applies to driving with snow chains. However, the gain in directional stability and steering control is far more important.
To keep the ABS fully functional, do not make any modifications to it. Work on the system must be performed only by authorized specialists.
Driving on mismatched tires, for example after installing a spare wheel (combined with the other three wheels fitted with winter-tread tires), may limit the functional capabilities of ABS. Therefore, reinstall the removed wheel as soon as possible.
A malfunction is indicated by the ABS warning lamp on the instrument panel (refer to the Controls and Instruments section). In this case, the brake system continues to operate normally, as on vehicles without ABS. However, contact an authorized BMW service center as soon as possible to have the brake system checked. Otherwise, difficult-to-detect faults may develop in the system.

Power Steering
If steering is heavy, check the fluid level as described in the Checking Fluid Levels chapter.
If difficulties occur when attempting to turn the steering wheel quickly, be sure to contact an authorized BMW service center for inspection.
If power steering fails, the effort required to turn the steering wheel increases.