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Departed · 9th April 2009, 12:18

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.

9th April 2009, 12:18	#14
Departed Retired -- Join Date: Jan 2007 Location: -- Posts: 3,785 Thanks: 0 Thanked 4 Times in 4 Posts	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.