Cadillac 2010 DTS Owner's Manual page 210

To access the passenger compartment air filter:
1. Use a tool to remove the cover. If the vehicle has
tabs that allow the cover to be unlatched with your
fingers, a tool will not be needed for this step.
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2. Then, insert a tool behind the push pin located on
the inboard side of the air filter compartment to
carefully pry the pin out.