2003 GMC Sonoma Owner's Manual - Page 280

7 If youchoose I I to perform the engine oil change service yourself, be sure the oil you use has the starburst symbol on the front of the oil container. If you have your oil changed for you, be sure the oil put into your engine is American Petroleum Institute certified for gasoline engines. RECOMMENDED SAE VISCOSITY GRADE ENGINE OILS HOT WEATHER LOOK FOR MIS SYMBOL You should also use the proper viscosity oil for your vehicle, as shown in the viscosity chart. RECOMMENDED COLD WEATHER DO NOTUSE SAE 1OW-40, SAE 2OW-50 OR ANY OTHER VISCOSITY GRADEOIL NOT RECOMMENDED 5-17