For the 960 and assuming same for S90: 1)shut all doors, hood, and trunk; 2)turn ignition on and off (without starting car) at least 5 times in quick succession and ending with it on (alarm LED should be blinking); 3)press either the lock or unlock button (but just one and once) on one remote within 15 seconds; 4)press a button on another remote within 10 seconds of the first and same for up to 2 more remotes (total of 4); 5)count to 10 and turn the ignition off; 6)test the remotes. This is from 2 Brickboard postings and a 3rd on a British site. Hope it works for you.