A method for warning a driver of a motor vehicle of an obstacle present in a side area next to a side flank of the vehicle using a driver assistance system, the method comprising:
- detecting the obstacle during a motion of the vehicle by an ultrasonic sensor stationarily arranged on a vehicle bumper at a front or at a rear of the vehicle, wherein the obstacle is detected before the obstacle leaves a detection area of the ultrasonic sensor and enters the side area next to the side flank;
- and
- after the obstacle leaves the detection area, estimating a current position of the obstacle in the side area relative to the vehicle by the driver assistance system, wherein the driver is warned by the driver assistance system in dependency on a result of the estimation.