Cadillac 2006 DTS Owner's Manual page 184

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.
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3. To remove the air filter, insert a tool between the air
filter and the compartment wall on the outboard
side of the vehicle. Then, push in to flatten the pin
holding the air filter in place. Gently remove the
air filter and any loose debris that may be inside the
air filter compartment.
4. Insert the new air filter by pushing until you hear a
click. Then, reinstall the push pin and snap the
cover into place.