NHTSA Preliminary Evaluation PE04031

ODI OPENED PE04-031 BASED ON EIGHT REPORTS OF ALLEGED POWER STEERING FAILURE IN THE SUBJECT VEHICLES.THE COMPLAINTS ALLEGE THAT THE DRIVER SUDDENLY LOST ALL ELECTRIC POWER STEERING ASSISTANCE WITHOUT WARNING MAKING THE VEHICLE DIFFICULT TO STEER. THE SUBJECT VEHICLE UTILIZES AN ELECTRIC POWER STEERING ASSIST SYSTEM (EPS) THAT PROVIDES VARIABLE STEERING ASSISTANCE BASED ON STEERING WHEEL TORQUE, STEERING WHEEL POSTION, AND VEHICLE SPEED.GENERAL MOTORS DOCUMENTS IDENTIFIED THE FOLLOWING TWO FACTORS THAT CONTRIBUTED TO THE ALLEGED DEFECT IN THE SUBJECT VEHICLES: A.CONTAMINATION OF THE TORQUE AND POSITION SENSOR FROM THESEPARATION OF GREASE APPLIED TO THE STEERING COLUMN ASSEMBLY. B.ELECTRICAL NOISE GENERATED ON THE POWER AND GROUND SLIP RING SURFACES OF THE TORQUE AND POSITION SENSOR.THE NOISE IS GENERATED AS THE SENSOR CONTACT BRUSHES MOVE ALONG THE SLIP RING SURFACES WHEN THE STEERING WHEEL IS ROTATED.ODI'S ANALYSIS SHOWED FAILURERATES THAT ARE OF CONCERN TO ODI AND INDICATED THAT THE ALLEGED DEFECT IS CONTINUING TO OCCUR IN THE SUBJECT VEHICLES. THIS PRELIMINARY EVALUATION HAS BEEN UPGRADED TO AN ENGINEERING ANALYSIS TO FURTHER INVESTIGATE THIS CONCERN, TO ASSESS THE POTENTIAL SAFETY-RELATED CONSEQUENCES, AND TO DETERMINE THE SCOPE OF THE AFFECTED POPULATION.