GMC 2003 Sonoma Owner's Manual page 279

You should also use the proper viscosity oil for your
vehicle, as shown in the viscosity chart.
If you choose 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.
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