This Preliminary Information communication provides information to the technician about vehicles that may have a Malfunction Indicator Lamp on. Technician may find a diagnostic trouble code P0324 set as a current or history. Also a rattle or spark knock type noise may also be heard while driving. Technician will need to let the vehicle cold soak overnight. Then clear the diagnostic trouble code in the Engine Control Module. Then use Global Diagnostic System 2 to monitor the Total Knock Retard Parameter. Let the vehicle run at idle for ten seconds with the park brake turned on. Hold the brake down and place the vehicle in ?Drive? for automatic transmission or drive gear for manual gear box then bring the engine between 1800 and 2000 RPM for 10 seconds then return to idle for 5 second. Repeat this cycle 7 times. If the readings during the raised RPM testing were NOT continuously above 6.0 degrees for more than 5 seconds, no further action is required within the scope of this bulletin. If the readings during the raised RPM testing were continuously above 6.0 degrees for more than 5 seconds, the vehicle requires repair. Technician will need to verify the engine oil level is correct. After insuring the engine oil level is correct allow the engine to idle for one hour. Every 15 minutes increase the engine rpms to 2000 and hold for 5 minutes. Or drive the vehicle for 25 to 30 miles. Allow the engine to cold soak overnight and then repeat the inspection procedure. Then review the Global Diagnostic System 2 session log Total Knock Retard Parameter. Technician will need to General Motors Technical Assistance Center for further assistance.