GM installed both factory keyless entry and seat memory as standard features on many Cadillac vehicles beginning more than a decade ago. Some vehicles had systems that used remotes with FCC ID L2C0005T. These included 2004-2006 SRX vehicles and 2005-2007 CTS sedans. SRX crossover SUVs used either a 3-button remote with lock, unlock and panic buttons or a 4-button remote that also had a rear hatch button. The CTS sedans used a 4-button remote with a trunk icon. (Some non-Cadillac vehicles also use a 4-button remote with FCC ID L2C0005T on the back, but these vehicles did not offer seat memory.) See all of the remotes with FCC ID L2C0005T at the following link:
Because these Cadillac vehicles had seat memory, the remote keyfobs have either a number ‘1’ or ‘2’ on the back. This is purely a cosmetic feature so that one can easily tell which fob is for driver 1 and which for driver 2. The keyfobs are identical otherwise and the remotes can be used interchangeably. In practice, the first fob programmed is associated with driver position 1 and the second with driver position 2, regardless of what fob number is on the back of the remote.
All of these Cadillac vehicles require a “scan tool” device to place the vehicle in programming mode so that it will allow synchronization with a new keyfob. So, the vehicle and all remotes to be used with it must be taken to a dealership or automotive locksmith for programming.