The switching points of the automatic transmission are controlled electronically and hydraulically (so-called EH control). This means that the hydraulic system of the automatic transmission is controlled by an electronic control unit, which selects the correct shift point depending on the vehicle speed and engine load.
To further harmonize the driver's individual driving style and driving modes, the automatic transmission is equipped with a sophisticated adaptive control system (AGS). When selecting gears along with various conditions such as uphill or downhill, slippery roads or stops and starts, this system takes into account the driver's driving style. AGS analyzes the position and movement of the accelerator pedal, vehicle speed, centrifugal acceleration (on bends) and deceleration when braking.
In accordance with the information received, the system evaluates the type of driver and switches to one of the four main programs available. In this case, a changeover can be made from the XE economy program via the E and S programs to the pronounced XS sports program. A driver with pronounced sporting ambitions, if necessary, can set the operating mode only according to the sports program by setting the operating mode selection lever to position 4. On slippery roads, an additional winter program is automatically activated (Wintarprogramm), allowing to increase traction and stability when driving.
Steptronic system - automatic with AGS and manual switching of driving modes
The Steptronic system installed on some models, along with automatic gear shifting, allows manual (step by step) gear shifting with the help of a second, short backstage. Step-by-step switching is typical for sports cars and motorcycles.
In automatic mode, for which the mode selector must be in position D when moving forward, automatic switching to one of five gears occurs using the adaptive control system. On the contrary, with the help of the left-hand link, the driver can shift gears at will. Moving the operating mode selector lever to the left from position D to position M retains the currently engaged gear. Subsequent pressing of the lever in the direction "+" or is accompanied by a shift to the driving mode respectively in a higher or lower gear.
Compared to conventional manual gear shifting, the Steptronic system is more advanced and comfortable and is equipped with protection against driver misconduct. Illegal engagements, such as downshifts at too high engine speeds, are ignored by the system. During acceleration, the system automatically shifts up without intervention from the driver until the engine speed limiter is activated. When accelerating using kick-down mode, the system automatically shifts to the lowest gear possible at the available engine speed.
When coasting, the Steptronic system automatically shifts to third gear in order to ensure sufficient traction during subsequent acceleration.
To assess the performance of automatic transmission and correct troubleshooting, experience with such gearboxes and expensive special devices are required.