I've been dealing with this problem for a while now. I have a '13 E70 x-drive N55. I had all 4 corners of the brakes replaced and the rear tires then I started getting the DSC light coming on very easily. It happens while going over moderate bumps and during hard acceleration and severely cutting engine power. The valvetronic actuator was bad and after it was replaced the problem did get a lot better but it is still there. The rear tires were replaced with the identical size pirelli p zero (315 35 20s) tires but they have a different tread pattern. I measured the circumference today and the rear tires are about 1/4" larger than the fronts. Can anyone tell me if this is the culprit?