VEHICLE STOPPED ON INCLINE OF A HILL, THEN REVERSED (GEAR SHIFT IN DRIVE) BACK DOWN 600 FEET THE HILL AND CRASHED AGAINST A CONCRETE WALL CORNER. HAVE 2 WITNESSES THAT SWITCHED OFF THE ENGINE, INSPECTED WRECK, FOUND NO FAULT CODES WITH A LAUNCH 431-READER BUT FIGURED THAT BATTERY WAS DRAINED AFTER 2 MONTHS. SURVIVING DAUGHTER SUFFERS FROM MEMORY LOSS BUT AT THE TIME OF THE ACCIDENT CLAIMS THE BRAKES FAILED.