Cadillac 2009 CTS - Manual (Page 325)

When to Add Engine Oil
If the oil level is within 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 5-133.
Notice: Do not add too much oil. If the engine has
so much oil that the oil level gets above the proper
operating range and into the upper cross-hatched
area on the dipstick, the engine could be damaged.
See Engine Compartment
Overview on page 5-14 for
the location of the engine
oil fill cap.
Add enough oil to put the level somewhere in the proper
operating range. Push the dipstick all the way back in
when through.
5-19