LIKE their sedan stablemates, most luxury four-wheel drives have an array of electronic aids to help the driver maintain control of the vehicle. Audi's electronic stability program (ESP) is one such system, which continuously monitors wheel rotating speeds and signals from steering angle, yaw rate and lateral acceleration. The electronics can detect, and then counteract, any oversteering or understeering tendency in the case of oversteer, ESP applies outer front-wheel braking in the event of understeer, the inner rear wheel brake is applied.