DRIVING DOWN THE FREEWAY AND THE DRIVER SIDE REAR TIRE LOCKS UP AND BRAKES BECOME HARD AS A ROCK, AND CAUSE ME TO SPIN OUT ON THE FREEWAY. RADIO CUT OFF AND FELT LIKE THE CAR WAS PICKING UP SPEED RATHER THEN SLOWING DOWN! ONSTAR THEN PROCEEDED TO TELL ME VIA EMAIL THERE IS AN ISSUE WITH MY ANTI BRAKING SYSTEM AND STABILITY TRAC SYSTEM AFTER THE CRASH.