Automatic stability and traction control system (ASC+T) (BMW 5 Series E39)

ASC + T system (Automatische-Stabilitats-Control plus Traktion) prevents the rear wheels from slipping when the accelerator pedal is depressed, for example when driving on wet surfaces. A slipping wheel transmits less traction and lateral force. The system is controlled by the ABS control unit. The control unit determines the instantaneous wheel speeds using sensors located at the wheels, the signals from which are also used by the ABS. If one rear wheel tends to slip, this information is transmitted from the ABS/ASC + T control unit to the digital engine electronics DME (Digitale-Motor-Elektronik). Based on this information, the DME changes the engine power by influencing the fuel injection duration of the injectors, in addition, the fuel injection advance angle can be changed. This control produces an effect similar to that which occurs when the driver takes his foot off the accelerator pedal. The engine power is quickly reduced and the wheels can now effectively interact with the road surface. If this does not happen, the T function is activated (traction control), and the slipping drive wheel is braked in measured doses. The driver will know about the activation of the T function by the blinking of the indicator on the instrument panel.

The system has the ability to regulate engine torque. It prevents short-term locking of the drive wheels on slippery surfaces by braking the engine crankshaft. At vehicle speeds of up to 40 km/h, the traction control system can function as a locking differential. Since the left and right wheels are braked independently of each other, the ASC+T system acts as a locking differential with an efficiency close to 100%.



The ASC + T system automatically detects any faults that arise. After the ignition is turned on, the indicator on the instrument panel lights up briefly and then goes out. If the indicator does not go out or lights up continuously while driving, this indicates that a fault has occurred. You can continue driving the car, but the ASC + T system will not work.

When driving with snow chains, in deep snow or when starting off in deep mud, it is advisable to switch off the ASC + T system using the switch located on the central console. When the switch is pressed again or the engine is started again, the system is switched on automatically.