In the car, press the central locking button (the one on the dash/by the handbrake depending on model, not the one on the fob) and hold it in until the doors lock and unlock, usually about 5 seconds.
Release the button.
Quickly (within 10 seconds) point the keyfob at the receiver (above the rear view mirror) and push the button on the fob. Doors should lock and unlock, job done.
You might have to repeat a few times.
frank
March 2012