This Preliminary Information communication provides information to the technician about vehicles that have an engine noise, low oil pressure, over-speed condition, or abnormal oil sludge build up in the crankcase. Technician should follow published Service Information diagnosis for the DTCs found. If an excessive amount of sludge is found in the crankcase the vehicle may be running a high percentage of Bio-fuel. Technician should verify the oil change records and verify proper oil change intervals are being followed. Technician should be advised to use the Duramax Diesel Owner?s Manual Supplement for guidelines on proper fuel usage.