Ok let me try another route,

If I brought a "reader" collar that sits around the steering barrel and two keys from breakers, and changed them with my main part of the keys that I have (blade, PCB & Case) basically swapping the immobilizer chip , would I then have two working keys?. Or is it a bit more involved than that?

Your right Jon, the dealership said they had never heard of this happening before just through the battery going flat on the car, and that is why I find it so strange just the chip is no longer reorganized by the ECU.

It wouldn't work, the coil round the lock only 'reads' the details which are checked by the immobiliser ECU which, if the details are recognised, allows the engine to start.

Dead right, the transponder chip is the immobiliser bit. The fob battery is irrelevant to this.

The transponder chip is matched to the EWS (immobiliser) ECU under the dash. The EWS is matched to the engine ECU. So you'd need to change all three to keep the immobiliser happy.

I think, but I'm not sure, that the transponder and EWS use a rolling code that they synchronise when you start up. So the EWS actually writes to the transponder chip. If this was corrupted because of the low battery, it might cause the problem you mention. I thought there was an option on T1 testbook to resync the immobiliser, but I may be wrong. If this is the case, then it won't be needed on new keys as they'll be made to be in sync as delivered.

The barcode is for the remot control, and is for aligning that with the BCM which looks after locking and alarm functions.

Sometimes keys just stop working.

I tried to use my spare unit that was kept on a hook the other day and it would not work. I replaced the battery and nothing. Dead as anything.

MMM, now who has a T1 that could give it a try?

I suspect Mr Lates may have T1 discs.......

Thanks David, its a long way to go, on a whim, T1 might not even work, I will PM Lates and see what he says, if he gets time to replay what with working on Les's tourer :lol:

Shame we can not get access to T1 or T4 at the meeting at Cosford

If it is the buttons that are not working, it may need re synchronising, have a look at the first paragraph in post 7.

Tony just a stab in the dark here !!:shrug:

Are you sure the Tiny chip didn't fall out perhaps when you had a look inside Keyfob?

If not perhaps swap the Transponder chips around between the 2 keys you have, and the "fault" should swap over to the new key.

Have you tried disconnecting Vehicle battery for 15 mins or so as the decaying charge on an old battery can make ECU's & BCU's behave in strange ways until a Power reset is implemented.