1998 Cadillac Deville remote key not working - has new batt

Hello,

The transmitter and the receiver are not synchronized. The receiver only opens the door if it receives the code it expects.
Try to resynchronize using this procedure

Turn the ignition key on and off eight times in less than 10 seconds. This tells the security system in the car to switch over to programming mode.

Press a button on all of the transmitters you want the car to recognize. Most cars allow at least four transmitters.

Switch the ignition off.
It should work, if not O' Reilly auto parts offers remote test for free.