Ben82 wrote:
Nothing needed with Lexia for the pairing of the fob, I actually needed to do it again for some reason. And did it without my laptop even in the car
Sounds like yours will be exactly the same as mine then.
Don't confuse pairing the fob with resynchronising it. What you describe where you put the key in the ignition, turn the key on and press the button on the fob will NOT pair a new fob, it will only resynchronise an already paired fob which has lost synchronisation and stopped working.
Pairing is the process of teaching the BSI (with a Lexia) the private key stored in the fob which is unique per fob, without this it won't recognise it.
In addition to this the fob uses a "rolling code" which means every time you press the button the fob transmits a different pseudo random code which is based on both its private key and a counter which increments each time you press the button.
When the BSI knows the private key of the fob and the most recently transmitted rolling code it can anticipate the next code that the fob will transmit and will not accept the same code twice in a row. This is to prevent someone simply recording the transmission and replying it later to unlock your car...(which they could do if the code was the same every time)
If you press the button outside the range of the receiver the fob moves onto the next rolling code for each press however the BSI receiver is still expecting the same code so they can get out of sync. To avoid this there is a "grace" window of about 20 codes which means that the BSI will accept not just the next expected code, but also any of the 19 that would follow after that.
In practice this means they will not get out of sync as long as you don't press the buttons on the fob more than about 20 times whilst out of range of the car - if you do they will lose synchronisation and the car will no longer respond to the fob until you do the resynchronisation process where you turn the key on and press the button.
Synchronisation can also be lost if the battery in the fob goes flat or is changed (it forgets where it was up to in the rolling code sequence) but this is not the same as it being unpaired - once paired the BSI will not forget the pairing unless you reprogram again with a Lexia and deliberately leave out the fob in the reprogramming process. (Now the BSI has truly forgotten the fob - for example if you were selling an excess fob and don't want the new owner to be able to open both their car and yours with the same fob!)
You can also unpair a transponder in a key by going through the Lexia reprogramming process and leaving out that key. The key will still open the door but it won't start the engine, nor will it silence the alarm when the ignition is turned on. My Xantia came with one fob and one spare key but the Lexia showed that the car was previously programmed for 3 transponders - so somewhere out there is another key that matched my car.
By reprogramming my actual keys the car will no longer let that mystery key start the car or silence the alarm. Call me paranoid but I thought it was worth doing.
but it's up to you....just like to see if it works and put everybodys mind at ease......from what simon(mandrake)says, it is logical that through a lexia, it should work, as he says,the bsi doesn't know whether the fob is new or old,so I will see how long the fob takes to arrive....hopefully before page 20 