Cadillac 2008 DTS Owner's Manual page 191

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.
3-50
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.