IN JULY OF 2007 THE OFFICE OF DEFECTS INVESTIGATION (ODI) OPENED PE07-037 TO INVESTIGATE ALLEGATIONS THAT THE REAR DIFFERENTIAL MAY FAIL CAUSING A LOSS OF MOTIVE POWER, AND IN SOME INSTANCES A LOSS OF CONTROL, IN MODEL YEAR (MY) 2004 THROUGH 2006 CADILLAC CTS, CTS-V, AND STS VEHICLES.AS A RESULT OF THAT INVESTIGATION GM ISSUED RECALL 07V-589 TO CORRECT A LEAKING PINION SEAL PROBLEM.EA07-017 WAS OPENED TO INVESTIGATE COMPLAINTS OF FRACTURED REAR DIFFERENTIAL HOUSINGS OR REAR HALF SHAFTS IN HIGH PERFORMANCE CADILLAC CTS-V VEHICLES.ACCORDING TO GM, THESE FAILURES RESULTED FROM THE CUMULATIVE DAMAGE FROM MULTIPLE POWER HOP EVENTS THAT CAN OCCUR DURING VERY AGGRESSIVE DRIVING. IN FEBRUARY 2008 INVESTIGATORS FROM ODI MET WITH GM REPRESENTATIVES TO CONDUCT TESTING OF THE SUBJECT CTS-V VEHICLES.DURING THE TESTING THE SUBJECT VEHICLES WERE SUBJECTED TO CONSIDERABLE TORSIONAL FORCES FROM STANDING STARTS AND WHILE DRIVING.POWER HOP OCCURRED DURING SOME OF THE MOST AGGRESSIVE DRIVING MANEUVERS.THE TESTING DID NOT RESULT IN FAILURE OF ANY REAR DRIVETRAIN COMPONENTS.THE ENGINEERING DESIGN AND TESTING DATA SUPPLIED TO ODI BY GM AND THE RESULTS OF THE TESTING CONDUCTED BY ODI TEND TO SUPPORT GM'S POSITION THAT THE DIFFERENTIAL DESIGN IS NOT DEFECTIVE. COMPLAINTS LISTED IN THE FAILURE REPORT DO NOT INCLUDE THOSE INDICATIVE OF FAILURE OF THE REAR PINION SEAL IN CTS-V VEHICLES COVERED BY RECALL 07V-589. FURTHER INVESTIGATION IN THIS MATTER WOULD NOT BE AN EFFICIENT ALLOCATION OF AGENCY RESOURCES.ACCORDINGLY, THIS INVESTIGATION IS CLOSED.SEE ATTACHED CLOSING REPORT FOR FURTHER DETAILS.