2002 key fob re-sync

[pappalem]

I know this subject has been covered at great length, but there seems to be a difference between the re-syncing of fobs in early and late model 406's.
Mine is a 2002 estate and the usual turn ignition on......press big button....... scenario does not work.
Could it be that I have bought a fob of unknown vintage ( after loosing my original )?
Does the fob need to be matched by age?
Is there another method of re-syncing?
Any help gratefully recieved, and all progress ( if any ) will be reported back.

[mjb]

re-syncing of fobs
...
Could it be that I have bought a fob

I think you're confusing 'coding'/'programming' with 're-syncing' here. Keys are made with a unique code, and that code is programmed into the car in the factory. You can order a new key at a dealer if you have the card that came with the car which contains the key's code (or can persuade them to look it up for you), but there is no known way of re-programming a car to a different code (you can't even do it with the dealer diagnostic tools!). You can't buy a 'blank' key either and have it coded to the car.

'Re-syncing' is required when either the battery in your key goes flat, or you've pressed the button too many times away from the car. This is because each time you press the key button, the key generates a new "password" if you like based on its code, which is sent out on its little radio transmitter. The car also generates this "password" in the same way and compares it to what it's received from the key. If the passwords are different, the car will try the next one the key should generate, then the next, then after a few times it gives up and you need to use the re-sync procedure. Why do they use a different "password" every time? Simple - if they just sent the code without changing it, what's stopping me from listening to it when you get in your car, then playing it back next time I see your car unattended? I believe this approach was used to steal a lot of early cars with remote central locking...

If the code in the key and the code in the car are different, it will never be accepted or able to re-sync!


Then there's also the passive RFID transceiver embedded in the keys of a lot of 406s which communicates in a very similar way with the immobiliser via an aerial mounted around the ignition barrel. This is a tiny lump of silicon stuck to the inside of the keyfob completely independent to the remote central locking circuitry and again, is uniquely coded with the car. I do think however that it's possible to code a car to a different RFID transceiver using dealer-level tools.


The upshot of this is, if you can, move the circuitry from your old keyfob to the new one and re-sync. If you can't, try moving the little RFID transceiver over, which should disable the immobiliser. If that's not possible and you haven't got a spare, you're going to have to hand over something over £100 to the dealers as well as proof of ID and ownership.

[pappalem]

Thamks for that.
It all makes sense now.
Looks like it's a trip to the dealer after all.

re-syncing of fobs
...
Could it be that I have bought a fob

I think you're confusing 'coding'/'programming' with 're-syncing' here. Keys are made with a unique code, and that code is programmed into the car in the factory. You can order a new key at a dealer if you have the card that came with the car which contains the key's code (or can persuade them to look it up for you), but there is no known way of re-programming a car to a different code (you can't even do it with the dealer diagnostic tools!). You can't buy a 'blank' key either and have it coded to the car.

'Re-syncing' is required when either the battery in your key goes flat, or you've pressed the button too many times away from the car. This is because each time you press the key button, the key generates a new "password" if you like based on its code, which is sent out on its little radio transmitter. The car also generates this "password" in the same way and compares it to what it's received from the key. If the passwords are different, the car will try the next one the key should generate, then the next, then after a few times it gives up and you need to use the re-sync procedure. Why do they use a different "password" every time? Simple - if they just sent the code without changing it, what's stopping me from listening to it when you get in your car, then playing it back next time I see your car unattended? I believe this approach was used to steal a lot of early cars with remote central locking...

If the code in the key and the code in the car are different, it will never be accepted or able to re-sync!


Then there's also the passive RFID transceiver embedded in the keys of a lot of 406s which communicates in a very similar way with the immobiliser via an aerial mounted around the ignition barrel. This is a tiny lump of silicon stuck to the inside of the keyfob completely independent to the remote central locking circuitry and again, is uniquely coded with the car. I do think however that it's possible to code a car to a different RFID transceiver using dealer-level tools.


The upshot of this is, if you can, move the circuitry from your old keyfob to the new one and re-sync. If you can't, try moving the little RFID transceiver over, which should disable the immobiliser. If that's not possible and you haven't got a spare, you're going to have to hand over something over £100 to the dealers as well as proof of ID and ownership.