For 1990-2009 cars

The Remote Function Actuation (RFA) system uses a continually changing code for increased security. Normally, the remote control door lock receiver will keep track of this changing code. However, loss of synchronization will occur if the transmitter is activated more than 256 times while out of range of the vehicle.

If the transmitter stops working, you may need to synchronize the transmitter to the vehicle remote control door lock receiver. In order to synchronize the transmitter to the vehicle remote control door lock receiver, press and hold the LOCK and the UNLOCK buttons for at least 7 seconds. If your vehicle is equipped with content theft deterrent, the horn will sound once the synchronization is complete.

Inspect the transmitter operation when the process is complete.