The fuel pump relay location on a 2001 Cadillac Deville is in the
underhood fuse block, also known as the power distribution center (PDC). It's not always clearly labeled as "fuel pump relay," so you might need to consult your owner's manual or a wiring diagram to identify the correct relay. The manual will have a fuse and relay diagram showing their locations and what each one controls.
Look for a diagram inside the fuse block cover itself – many times these are printed right on the inside of the cover. If not, consult your owner's manual.