ODI OPENED PE03-057 TO ASSESS PARKING BRAKE INEFFECTIVENESS IN THE SUBJECT VEHICLES.THESE VEHICLES ARE EQUIPPED WITH FOUR WHEEL DISC BRAKES THAT INCORPORATE A SINGLE-SHOE DRUM-IN-HAT PARKING BRAKE INDEPENDENT OF THE SERVICE BRAKES.COMPLAINT AND WARRANTY DATA INDICATE THAT THE PARKING BRAKE LININGS TEND TO WEAR OUT EARLY IN THE LIFE OF THE VEHICLE (AT AN AVERAGE OF 24 MONTHS IN SERVICE), REDUCING THE PARKING BRAKE SYSTEM'S TORQUE BELOW THAT NEEDED TO IMMOBILIZE THE VEHICLE.GM HAS ATTRIBUTED THIS ACCELERATED WEAR TO FOREIGN MATERIAL INTRUSION AND A FAILURE OF THE BRAKE SHOE TO PROPERLY SELF-CENTER WITHIN ITS BRAKE DRUM.EFFECTIVE WITH THE START OF MY 2003 PRODUCTION, A NEWER REDUCED FORCE HOLD-DOWN CLIP WAS INTRODUCED TO FACILITATE BRAKE SHOE DISENGAGEMENT FROM THE DRUM SURFACE.THIS PART IS ALSO AVAILABLE AT THE SERVICE LEVEL FOR THE MY 1999-2002 VEHICLES.GM HAS INDICATED THAT THE PAKING BRAKE IS INTENDED TO OPERATE IN CONJUNCTION WITH THE TRANSMISSION TO IMMOBILZE PARKED VEHICLES, AND THAT IN MANY CASES, ACCELERATED PARKING BRAKE LINING WEAR IS CAUSED BY ROUGH USE, VEHICLE MODIFICATIONS, AND DRIVING WITH THE PARKING ENGAGED. ODI HAS UPGRADED THE PRELIMINARY EVALUATION TO AN ENGINEERING ANALYSIS TO GATHER FURTHER INFORMATION CONCERNING PARKING BRAKE USAGE FACTORS AND THE CIRCUMSTANCES SURROUNDING THE SEVENTEEN REPORTED VEHICLE CRASHES.