This Preliminary Information communication advises the technician that the 6.6L diesel engine Regular Production Option Code (L5P) following fuel system part numbers 2678990 (Right Side Fuel Rail), 12678991 (Left Side Fuel Rail), 12678992 (Fuel Injector), 12676904 (Fuel Injection Pump), 12647909 (Fuel Pressure Sensor) and 55495697 (Valve Kit) will be placed on a parts restriction through the General Motors Product Quality Center. Dealer will need to contact General Motors Product Quality Center for further assistance.