The spoiler will deploy as a safety precaution if the ESP system detects a large difference in the wheel speed between the front and rear wheels. This could occur as a result of the speed signal malfunction, or could occur if the vehicle is attempting to accelerate on a low friction surface causing the rear wheel to spin. The spoiler will remain deployed and the warning light in the spoiler switch will blink until the vehicle is restarted. IF the spoiler continues to deploy in this fashion below the normal deployment speed, see you authorized dealer.