GMC 2009 Sierra - Manual (Page 326)

When to Add Engine Oil
If the oil is below the cross-hatched area at the tip
of the dipstick, add at least one quart/liter of the
recommended oil. This section explains what kind
of oil to use. For engine oil crankcase capacity,
see Capacities and Specifications on page 5-116.
Notice: Do not add too much oil. If the engine
has so much oil that the oil level gets above
the cross-hatched area that shows the proper
operating range, the engine could be damaged.
See Engine Compartment
Overview on page 5-12
for the location of the
engine oil fill cap.
Be sure to add enough oil to put the level somewhere
in the proper operating range. Push the dipstick all
the way back in when you are through.
5-14