remote quit working

The only way I know of to check the remote lock receiver on your 1997 Cadillac DeVille is with a known good remote. If your old remotes have stopped working you can try "re-synchronizing them buy pressing and holding the lock and unlock buttons simultaneously (one remote at a time). When synchronizing is complete the lights will flash and the horn will cycle. If that does not work you may need to try programing a new remote to see if the receiver will work. If the door lock receiver will not enter the programing mode then power and ground to the receiver should be checked. If power and ground to the receiver are OK and it will not enter the programing mode the it may need replacing.