Car driven normally on cold, clear night. Road condition was fair (dry from centerline to travel lane midpoint w/ hard-packed snow from there to shoulder). Experienced a vibration, squealing noise & slight pull to right. Stopped to investigate possibility of blown tire. Found nothing wrong after visual inspection, so resumed driving. Approx. 15S later, squealing, vibration & sensation of pulling to right returned, then car would not respond to throttle inputs & slowed from 40 to 25mph. Car then shuddered violently w/ loud screeching noise, snapped to right & lost control. Attempts to counter steer were ineffective as car slid on hard-packed snow for approx. 100' & struck snowbank at 20mph. Fortunately snow was very light, dry and fluffy & deceleration was reasonably gentle. No major damage occurred & air bags did not deploy. After extricating, car could not be driven. An observer standing outside the car noted front right wheel would roll for a few feet, then lock up. Shut engine off & restarted (attempting to reset systems). At this point both 'bas esp' and 'ABS' warning lights illuminated (they were not lit previously). Car still could not be driven - front right wheel would lock up after a few feet of travel & had to be towed away. Later determined incident caused by yaw sensor failure. Front right wheel had been locking & sliding on hard packed snow then suddenly regained traction when it crossed a dry patch of pavement, causing the rapid directional change & loss of control. Very dangerous. If car had hit a tree, parked car, etc. Instead of soft snowbank this would have been a serious crash likely w/ injury. Unacceptable & unsafe! please reopen investigation! this is a potentially very dangerous system! sensors should continuously self-check & shut system off completely if failed. This will kill someone eventually if nothing is done!

- Kingston, NH, USA