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2005 C4 key replacement

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Author Post
Sun May 31 2020, 04:43am
Member No: #54131
Joined: Jul 10 2019
Location: Ireland
Hi all.
My father in law damaged key for his 2005 C4. Key fell on the hard floor and was unable to start the car anymore. Lock/unlock function was working. We called mobile lockmith. He replaced immobiliser chip and reprogrammed the key. Now the key was able to star tthe car but locking function was lost. Locksmith was able to confirm that key still transmits signal to the car. No answer from him why this happened as we still hav ethe original key...
OK. I've ordered online two different new blank keys. Programmed those keys with Lexia. They start the car. Still, no matter how many times we tried resync procedure, still no luck.
Can anyone tell me what is wrong? I understand that maybe aftermarket keys are hit and miss but what about the original key that came with the car???? It is clear that falling to the floor did not damaged keys ability to lock the car as it was operational before locksmith replaced chip.

If someone know the answer or has some ideas, please let me know.

Thank you all.
Sun May 31 2020, 07:54am

Member No: #82
Joined: Jan 22 2007
Location: Hoylake
They might need to be re-paired.
- Click Here -
Sun May 31 2020, 06:42pm
Member No: #54131
Joined: Jul 10 2019
Location: Ireland
thanks for information. I knew this already. Let's leave all aftermarket keys aside for now. Why we can't resync original key? I mean it is confirmed by locksmith that the key is still able to transmit signal to the car. Only immobiliser chip was replaced and key was programmed to the car. Before the remote locking was working even when key was unable to start the engine. Why original key that came with the car from the factory can't be resynced to the same car? I do not understand this. Yes, aftermarket keys are hit and miss. To be honest I was surprised that both keys were programmed to the car in few minutes. I was thinking that this part will be the hardest and resync procedure will be easy sailing.... well it is backwards now....
Mon Jun 01 2020, 03:31pm
Member No: #27768
Joined: Oct 13 2012
Location: Hove
Did you try re-syncing the original key using the link in John's post?
Tue Jun 02 2020, 02:10pm
Member No: #54131
Joined: Jul 10 2019
Location: Ireland
Yes I did. Many attempts. No luck. I believe locksmith did the same. I mean I believe he should know how it is done. Well for some reason it is not syncing. As I've said before, key is still able to transmit correct signal.
As far as I understand there are two systems: one for starting the engine and another for remote locking. One was fixed after adding new immobiliser chip and so the engine starts. No issues there. Another system was not changed. And yet for some reason that system is not working. No changes were made to car. So my logic tells me that locking function MUST work. The question is HOW to make it work again?
I believe that Lexia is useless in this case. This tool can be used only for programming the key.

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