BY LETTER DATED DECEMBER 12, 1999, GM NOTIFIED NHTSA OF ITS PLANS TO CONDUCT A SAFETY RELATED DEFECT CAMPAIGN TO REMEDY 155,149 OF THE SUBJECT VEHICLES.THE VEHICLE POPULATION FOR THE CAMPAIGN INCLUDES THE 1997 BUICK REGAL/CENTURY AND PONTIAC GRAN PRIX MODELS BUILT DURING THE PERIOD FROM THE START OF PRODUCTION THROUGH MAY 1, 1997.GM DETERMINED THAT THE WIPERS INSTALLED PRIOR TO THIS DATE COULD STOP WORKING, USUALLY DURING HEAVY LOAD CONDITIONS, DUE TO SEPARATION BETWEEN THE DRIVE PIN AND THE CRESCENT IN THE WIPER CRANK ARM ASSEMBLY.EFFECTIVE MAY 1, 1997,GM CORRECTED THIS PROBLEM IN PRODUCTION BY MODIFYING THE DRIVE PIN AND STRENGTHENING THE CRESCENT.THESE SAME IMPROVED PARTS WILL BE INSTALLED IN THE VEHICLES TO BE RECALLED.THE SCOPE OF THE CAMPAIGN WILL INCLUDE ALL VEHICLES PRODUCED PRIOR TO THE MAY 1, 1997 CORRECTION (THE OLDSMOBILE INTRIQUE PRODUCTION DID NOT START UNTIL AFTER MAY 1, 1997, AND IS THEREFORE NOT INCLUDED).VEHICLES WITH THE SCOPE OF THIS INVESTIGATION AND PRODUCED AFTER MAY 1, 1997, CONTAIN THE MORE ROBUST CRESCENT AND IMPROVED PIN DESIGN AND ARE NOT INCLUDED IN THE RECALL CAMPAIGN.ODI WILL CONTINUE TO MONITOR COMPLAINT REPORTS ON THE VEHICLES PRODUCED AFTER MAY 1, 1997 AND RESERVES THE RIGHT TO TAKE FURTHER ACTION IF WARRANTED BY THE CIRCUMSTANCES.BASED ON GM'S RECALL ACTION (ODI 99V-348) THIS INVESTIGATION IS CLOSED.