Some of the circuits in the key are slightly different, even when the keys look the same, I programmed some Yaris keys at the start of the year, the car came with one key that had no buttons left in it, the first key I got hold of second hand wouldn't work for the locks, it started the car but just couldn't get the buttons to work, I tried a different chip/button part of the key and got all of it working so then got hold of another the same and managed to program a spare as well.